SUSTAINABLE CONTROL OF INTERNAL PARASITES OF SHEEP (SCIPS)
A SUMMARY OF R ECENT AND C URRENT R ESEARCH ON C ONTROL OF I NTERNAL PARASITES OF S HEEP
Editors: L.P. Kahn and D.L. Watson
Table of Contents
Introduction.........................................................................................................................................2
Improved diagnostic techniques......................................................................................................4
Flow cytometry and fluorescent staining .......................................................................................... 4
Faecal antigen detection ................................................................................................................. 4
Specific PCR assay ........................................................................................................................ 5
Pasture larval counts of gastro-intestinal parasites of sheep .....................................................6
Review of pasture larval counts....................................................................................................... 6
Application of pasture larval counts in South Australia ...................................................................... 6
Parasite management software ......................................................................................................7
Pharmacokinetics and metabolism of anthelmintics ....................................................................8
Prevalence of anthelmintic resistance............................................................................................9
A New South Wales perspective ..................................................................................................... 9
A Western Australian perspective .................................................................................................... 9
A South Australian Perspective ..................................................................................................... 10
Research on macrocyclic lactone resistance ..............................................................................11
Development of macrocyclic lactone resistance ............................................................................. 11
Genetics of avermectin resistance................................................................................................. 11
Scouring in sheep ............................................................................................................................13
Partial flock drenching to minimise selection for drench resistance........................................14
“Smart Grazing” ...............................................................................................................................15
Effects of nutrition on resistance to infection ..............................................................................16
Protein supplements .................................................................................................................... 16
Non-protein nitrogen supplements................................................................................................. 16
Trace elements ............................................................................................................................ 16
Breeding worm resistant sheep.....................................................................................................18
Nemesis project ........................................................................................................................... 18
Genetic markers for parasite resistance......................................................................................... 18
Blood antibody levels – the use of the Host Resistance Test ........................................................... 19
Relationship between resistance to worms and lice ........................................................................ 19
Vaccines............................................................................................................................................21
Worm vaccines based on concealed antigens ................................................................................ 21
Worm vaccines based on conventional antigens ............................................................................ 21
Irradiated larval vaccine ................................................................................................................ 22
Boosting immunity in young lambs ...............................................................................................23
Biological control of parasitic nematodes ....................................................................................24
Copper oxide wire particles for Haemonchus control ................................................................25
Condensed tannins to assist worm control..................................................................................26
Acknowledgments ...........................................................................................................................27
Appendix – Contact details for contributors ................................................................................28
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
INTRODUCTION
In late 1998 The Woolmark Company (now
Australian Wool Innovation Ltd, or AWI)
commissioned a thorough reappraisal of its
projects on internal parasites of sheep and the
preparation of a comprehensive business plan for
future endeavours in this area. The widespread,
and increasing, emergence of anthelmintic
resistance to all known classes of anthelmintic
drugs was the single most important factor driving
the synthesis of a program focussed on
sustainable, cost-effective control of internal
parasites.
After extensive consultation with
woolgrowers, researchers, consultants and
extension workers, a plan was developed and
adopted. Known as SCIPS (Sustainable Control
of Internal Parasites of Sheep), the program of
research, education/training and technology
transfer was offered by tender and contracted out
in 1999, and work began in early 2000.
resource material on sheep worm control in
Australia. Considerable progress has been
made in establishing the website, and
although it is by no means complete it is
accessible at www.sheepwormcontrol.com.
Additionally, a discussion forum has been
established for use by professionals involved
in worm control (www.vetsci.usyd.edu.au/cgibin/scips/Ultimate.cgi).
•
Project 4.
Increased knowledge of
sustainable control of internal parasites
through targeted education/training courses
(Veterinary Health Research Pty Ltd,
Agriculture Western Australia, and University
of New England). This is an education and
training module.
A series of Professional
Research
Update
seminars,
delivered
throughout Australia, has recently been
completed.
In 2001 training courses on
sustainable parasite control will be offered to
drench resellers in woolgrowing regions
across the country.
A similar series of
seminars/courses for woolgrowers is also
being planned.
•
Project 5. Accelerating adoption of Nemesis
technology (breeding parasite resistant
sheep) by Australian woolgrowers (CSIRO
Livestock Industries & regional collaborators,
University of Melbourne).
This is
predominantly a technology transfer module
designed to increase the adoption of breeding
for worm resistance throughout the industry.
CSIRO has appointed a Technology Transfer
Specialist for the project and is working with
collaborators in each of the States. Staff at
the Mackinnon Project (University of
Melbourne) are using a “push-pull” strategy to
increase the availability of rams sold with
faecal egg count estimated breeding values
in Victoria, working with leading commercial
woolgrowers and studs.
•
Project 6. Characterising the relationships
between scouring and genetically-based
resistance to internal parasites in various
environments (Agriculture Western Australia,
CSIRO Livestock Industries). Work has just
commenced on this research module, which
aims to determine (in a winter and a summer
rainfall environment) whether breeding sheep
with enhanced genetic resistance to worms
increases the problem of scouring/ diarrhoea/
dagginess.
The research phase of the
project is due for completion in May 2003.
The SCIPS projects that are currently in progress
are:
•
Project 1. Identification of the most costeffective methods for accurately diagnosing
internal
parasite
infestations
(CSIRO
Livestock Industries, Agriculture Western
Australia, NSW Agriculture). This is a shortterm research project with a finishing date of
June 2001. The objectives of the project are
to quantify the cost, accuracy and turnaround time of several technologies with the
potential to supersede or complement current
techniques for diagnosing parasite burdens;
and to develop national quality assurance
guidelines for parasite diagnosis.
•
Project 2. Development and field validation
of computer simulation models of internal
parasite infestations (CSIRO Livestock
Industries, Agriculture Western Australia).
Work has just commenced on adapting the
single species simulation model ‘Wormworld’
into a combined three species model
(Haemonchus,
Ostertagia
and
Trichostrongylus).
Field validation of the
model is also underway in a winter and a
summer rainfall environment. The project is
due for completion in February 2003.
•
Project 3.
Development of a national
information database and website to serve as
an
information/advice
resource
for
sustainable control of internal parasites
(University
of
Sydney
&
regional
collaborators). This is a communication and
education/training module for SCIPS, based
on a comprehensive update of technical
This document, “A Summary of Recent and
Current Research on Control of Internal
Parasites of Sheep”, is being distributed as a
supplement to the recent SCIPS Professional
SCIPS – page 2
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
Research Update seminars. It is not a formal
literature review, rather a synopsis that has been
compiled to provide industry professionals with a
‘snapshot’ of the research frontiers in the late
1990's/early 2000's in the area of internal
parasites of sheep, with particular emphasis on
the Australian industry.
For those seeking more detailed information or an
entree to the scientific literature the Appendix
provides a comprehensive list of key personnel
and their contact details. Further information on
SCIPS can be obtained from Dr Dennis Watson
SCIPS – page 3
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
IMPROVED DIAGNOSTIC TECHNIQUES
Faecal egg counts (FEC) and larval differentiation
are the basis for diagnosing the severity of and
species present in gastro-intestinal nematode
infections. Nevertheless, the techniques used in
diagnosis have not really improved over the 40
years since the development of the McMaster
slide. There are a number of disadvantages
associated with FEC and larval differentiation,
including considerable variation in FEC between
faecal samples taken from the same sheep, and
variation between nematode species in their
development during culture. Furthermore, FEC
are unable to indicate a worm burden until egg
laying commences at three to four weeks after
infection, by which time the worms are well
established and the host may already be suffering
adverse effects.
The increasing spread of anthelmintic resistance
on Australian sheep farms has resulted in a
change from the large region-based drenching
programs to drenching strategies devised for
individual farms. Decisions on when to drench,
therefore, depend increasingly on FEC of sheep
from the individual farm. Thus, many more FEC
are being done. In addition, FEC provide the
basis for genetic selection programs for
resistance to internal parasites.
This section provides a summary of a number of
different diagnostic procedures currently being
developed and evaluated with the aim of
providing a superior diagnostic test to FEC.
Flow cytometry and fluorescent staining
Current research funded by AWI through its
SCIPS program and conducted by Dr Leo Le
Jambre and Dr Ian Colditz, CSIRO Livestock
Industries, is comparing enumeration and species
differentiation of nematode eggs in faeces by flow
cytometry with the conventional McMaster light
microscope method and larval culture.
The
advantages of flow cytometry over conventional
methods include greatly increased sample size,
thus reducing variation between samples in FEC,
and decreased time taken for species
differentiation since differentiation is performed
on eggs rather than larvae.
Sample preparation for egg counting by flow
cytometry initially uses the McMaster salt flotation
method but is followed by centrifugal separation
of eggs and addition of an internal standard. Egg
counting is performed mechanically by the flow
cytometer. Species differentiation of nematode
eggs is performed using a similar process with
the exception that eggs are specifically stained
prior to analysis. In results so far, flow cytometry
compares favourably with conventional faecal
culture and larval differentiation.
There is also an opportunity under the SCIPS
project to develop a protocol for a national interlaboratory self-assessment program for worm
diagnostic techniques.
The NATA-accredited
Parasitology Laboratory at Agriculture Western
Australia has developed standard procedures for
Quality Assurance Assessment of worm egg
counts, while NSW Agriculture’s EMAI has
provided an inter-laboratory proficiency testing
program for faecal egg counts, larval identification
and liver fluke counts, by co-ordinating the
preparation, distribution and analysis of single
species and mixed species faecal cultures. The
Standing Committee on Animal Health Laboratory
Standards (SCAHLS) has indicated that
standards need to be established in parasite egg
counting and larval differentiation.
NSW
Agriculture has recently offered to co-ordinate a
national assessment program for parasitology
testing to SCAHLS. The SCIPS Project will allow
self-assessment techniques to be standardised
between NSW Agriculture and Agriculture
Western Australia by the exchange of
assessment protocols between laboratories and
the development of a validated standard
operating assessment technique.
Faecal antigen detection
The presence of worms in the gut of a sheep
results in the passage of a range of proteins in
faeces that would not otherwise be present. The
detection and characterisation of such proteins
offer the prospect of improved methods of worm
diagnosis.
A prototype faecal antigen detection test has
previously been developed by Agriculture
Western Australia (current contact: Dr Dieter
Palmer) with support from AWI. The test is an
antigen capture ELISA designed to identify and
quantify burdens of the major nematodes, hence
removing the need for worm egg counts and
larval differentiation. The test showed promising
results when evaluated on penned sheep infected
with different parasite burdens. However, it did
not prove as encouraging when evaluated in the
field, with results varying from acceptable to poor
against different worm genera. Investigation of
the problems with the test is continuing, although
considerable further development will be needed
before a useful field test could become available.
Dr Khosse Mitri and Dr Mark Sandeman, La
Trobe University, have been following a similar
approach. Protein separation procedures clearly
show many antigens specific to faecal samples
taken from sheep infected with H. contortus or O.
SCIPS – page 4
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
circumcincta. The isolation and sequencing of a
range of these proteins reveal that most are
parasite-derived
with
some
pathologyassociated, host molecules also present.
Therefore, these parasites apparently release a
wide range of proteins that are able to survive
passage through the gut. These proteins are
associated with different developmental stages
of the parasite and with damage to host tissues
at various points during the infection.
The diagnostic value of these antigens was
tested by ELISA using antibodies specific and
sensitive to the target copro-antigens. Results
indicate that several of the copro-antigens are
potential candidates for the development of
specific and sensitive ELISAs for the early
detection of haemonchosis or ostertagiosis. The
ELISA is able to detect infection as early as five
(Haemonchus) and eight (Ostertagia) days post
oral infection during the prepatent period and
well before the appearance of parasite eggs in
faeces.
The response also appears to be
quantitative. Specificity has been tested for one
of the Haemonchus antigens, and the ELISA
was found to be highly specific for this species in
sheep. Initial work with Trichostrongylus spp
suggests hat the same techniques are
applicable and should be able to detect specific
faecal proteins for a wide range of parasites and
hosts.
Specific PCR assay
Faeces passed from infected sheep also contain
nucleic acids from the parasitic nematodes
present. Dr Robin Gasser, Dr Ian Beveridge
and Dr Neil Chilton, University of Melbourne,
have been investigating the application of a
highly sensitive DNA test system (i.e. the
polymerase chain reaction, or PCR) to detect
the DNA of individual species of nematode. The
potential advantages of this technique are
increased rapidity, and sensitivity and specificity
of detection, particularly as infections can be
detected before nematode eggs appear in
faeces. The specific PCR assay obviates the
need for faecal culture and larval differentiation
and is potentially able to semi-quantify the level
of infection. Although this methodology is not
yet available commercially, it provides an
alternative prospect for improved diagnosis in
dedicated
service
laboratories.
SCIPS – page 5
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
PASTURE LARVAL COUNTS OF GASTROINTESTINAL PARASITES OF SHEEP
Review of pasture larval counts
A review of recent literature and a survey of
veterinary
diagnosticians
was
recently
undertaken for AWI by livestock industries
consultant, Dr Dennis Watson, to evaluate the
practicality and cost-effectiveness of pasture
larval counts (PLC) as a diagnostic and
predictive tool for sheep nematode parasite
burdens. Interest in PLC has arisen from the
recognition that numbers of infective larvae on
pasture may be a useful management tool for
integrated parasite control.
Pasture larval counts involve direct human
sampling of pasture herbage by plucking
(designed to simulate the grazing animal) in a
designated pattern across a chosen area of
pasture. Pooled herbage samples are then
subjected to extraction procedures, and
nematode larvae recovered, identified and
quantified.
From the literature reviewed it is clear that PLC
have been successfully used as a research tool
and for this purpose they have merit. Even as a
research method, however, there remain serious
concerns about their accuracy and validity - first
in terms of the pasture samples collected being
representative of the herbage ingested by
sheep, and second, in the laboratory in terms of
the reliability of recovery of larvae from pasture
and accuracy of larval identification and counting
in the presence of free-living nematode species.
There is little or no encouragement in the
scientific literature to extend PLC from its
research use to a more widely available
diagnostic/predictive tool for use as a
management aid on grazing properties.
failing dramatically within 1-2 years due to heavy
worm infections.
In a study over 2 years on 4 pivot systems,
lambs were introduced in December after
paddocks had been destocked of sheep for at
least 3 months. Immediately prior to introduction
sheep were drenched with moxidectin and held
aside for worm eggs to clean out. Thereafter no
drenches were given to lambs grazing the pivot
area. Cattle grazed the pivot either together with
or following the sheep. Sheep were removed
from all systems within 3-6 months and replaced
by cattle.
Pasture larval counts and worm egg counts
remained consistently low throughout both
summers, demonstrating the importance of
restricting contamination in the previous spring
and ensuring that lambs carry no residual
infection on to the pasture. Levels of sheep
worm larvae on pasture rose in autumn, by
which time the sheep had been marketed.
Levels remained stable for 2 months and then
declined.
The study demonstrated that profitable,
sustainable production of prime lambs under
pivot irrigation over the summer months is
possible, provided very strict conditions of
pasture preparation and flock sanitation are
followed.
The PLC review will shortly be available on the
SCIPS website (www.sheepwormcontrol.com),
or alternatively, it can be obtained from Dr
Dennis Watson.
Application of pasture larval counts in South
Australia
One supporter of pasture larval counts is Dr Ian
Carmichael, of SARDI Livestock Systems,
South Australia. Dr Carmichael has recently
applied the technique to evaluate the viability of
pivot irrigation systems in south-eastern SA.
Pivots operate between November to March to
enable prime lambs to be grown out at a time of
market shortage. The single most important
constraint to the current and future success of
pivot farming systems is an inability to control
Trichostrongylus vitrinus, with most systems
SCIPS – page 6
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
PARASITE MANAGEMENT SOFTWARE
Field trials to evaluate new or modified methods
for the control of internal parasites of sheep are
extremely time-consuming, expensive and
virtually impossible to replicate in a wide range
of environments. To overcome these difficulties,
a simulation model of the population dynamics
and genetics of worms (‘Wormworld’) has been
developed by Dr Robert Dobson and Ms Liz
Barnes, CSIRO Livestock Industries, with
support form AWI.
The development and
survival of the free-living infective stages of the
parasite on pasture are controlled by climatic
data such as rainfall, temperature and
evaporation. This information is made available
to the model on a daily basis from weather files
for the locality in which it is desired to test the
control program.
The model can be used to explore the potential
effectiveness of control technologies still under
development, such as genetically resistant
sheep, worm vaccines or biological control, as
well as modifications of current strategies,
including drenching programs, nutrition, grazing
management, stocking rates, and lambing and
weaning times. The model could be used, for
example, to predict the efficacy of worm control
and the development of drench resistance over
a 20-year period in Albany, WA, under a one or
two summer drench worm control program.
(Another example is discussed in the section on
‘Research on Macrocyclic Lactone Resistance’
below.)
Currently, there are three separate models, for
each of Trichostrongylus colubriformis (Black
Scour Worm), Ostertagia spp (Small Brown
Stomach Worm), and Haemonchus contortus
(Barbers Pole Worm). A new project under the
SCIPS program, with AWI funding, will see the
three species combined into a single model.
Two-year field trials at Chiswick (Armidale NSW)
and Albany WA, to further validate the model,
are also underway as part of the project.
After validation testing, it is likely the predictive
model will be made available to users as a
module in CSIRO’s Farmwi$e software. When
used
together,
Farmwi$e
will
provide
Wormworld with data on feed intake and
herbage density and the worm model will
provide Farmwi$e with data on inappetence and
deaths attributed to worms. In this way the
software will provide better estimates of
production benefits under different grazing
management systems.
SCIPS – page 7
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
PHARMACOKINETICS AND METABOLISM OF
ANTHELMINTICS
The Australian sheep industry currently relies
heavily on the use of anthelmintics to control
internal
parasites.
Broad
spectrum
benzimidazole (BZ) drenches were first released
in 1961 and the release of other anthelmintic
groups followed over the next 35 years, the most
recent addition being that of moxidectin in 1995
and the re-release of naphthalophos in the same
year. The release of new anthelmintic groups
has been followed by the development in worms
of resistance to the anthelmintic. Resistance to
BZ drenches now exists on 90% of Australian
sheep farms. For the foreseeable future there is
little prospect of novel anthelmintic compounds
with unique modes of action becoming
commercially
available.
Therefore
it
is
imperative that existing drenches are used in
ways that preserve their efficacy for as long as
possible.
tract. A reduced rate of passage of digesta
prolongs the time for drug absorption and
recycling. Dr Hennessy has demonstrated that
withholding feed for 1 day prior to drenching with
BZ, and, for maximum effect for 6 h after, slows
the movement of digesta through the gastrointestinal tract and increases the exposure time
of parasites to the drug, resulting in a greater
reduction in worm numbers. Trials with sheep
infected with BZ resistant H. contortus and T.
colubriformis have shown that withholding feed
is more effective than doubling the dose rate in a
single drench. In a practical context the
effectiveness of BZ drenches against BZ
resistant parasites can be greatly improved by
withholding sheep from feed for one day prior to
drenching.
Dr Des Hennessy, CSIRO Livestock Industries,
has developed strategies that improve the
efficacy of BZ drenches.
These improved
strategies are based on detailed knowledge of
the whole-body pharmacokinetics of BZ
drenches. The approach taken by Dr Hennessy
and incorporated into the improved drenching
strategies has been to maximise the duration of
exposure of the nematode to the drug. The
most effective means of increasing the duration
of exposure are (1) following the correct
drenching technique and (2) slowing the rate of
movement of the drug through the animal. Dr
Hennessy has demonstrated that with BZ
drenches it is the length of exposure to the drug
rather than the maximum drug concentration
that is the key to effective drenching.
The correct drenching technique ensures
placing the drench-gun tip over the tongue to
direct the entire dose down the throat and into
the rumen. Placement of the drug into the
rumen is important because it is the rate of flow
of digesta from the rumen that defines the
duration over which the drug is presented to the
parasite habitat. Incorrect placement of the
drench-gun may result in closure of the
oesophageal groove allowing some or all of the
drench to pass to the abomasum and greatly
reducing the duration of the anthelmintic action.
Field trials have demonstrated that as many as
60% of drenched sheep may not receive the
entire dose into the rumen.
The second means of increasing the duration of
exposure of the nematode to BZ drenches is by
slowing the rate at which digesta moves out of
the rumen and through the gastro-intestinal
SCIPS – page 8
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
PREVALENCE OF ANTHELMINTIC
once pasture growth resumes in winter, if not
diluted with non-selected worms.
RESISTANCE
A New South Wales perspective
Resistance to sheep drenches is widespread,
with probably 90% or more of farms having
resistance problem. Following is an overview by
Dr Stephen Love, NSW Agriculture, of the
current resistance situation, with particular
reference to NSW.
Drench or Drench Group
Benzimidazole
(BZ)
or
“White”
drenches
Levamisole (LEV) or “Clear” drenches
Combination (BZ + LEV) drenches
Macrocyclic Lactone (ML) drenches
®
Naphthalophos (Rametin )
Closantel
®
Triclabendazole (Fasinex )
In the dry areas, one summer drench per year is
typical, and resistance to MLs has evolved on
some farms after four to six years. In the higher
rainfall areas, there are farmers who have used
MLs for eight years in a row, two to four times
per year, with no evidence of resistance
developing.
Prevalence of Resistance*
Approximately 90% of properties.
Approximately 80% of properties.
Approximately 60% of properties.
No longer rare; eg in WA, a recent series of faecal egg count
reduction trials (FECRTs) showed 38% of farms had MLresistant Ostertagia. In northern NSW, 10-20+ farms have MLresistant Haemonchus. ML resistance in Ostertagia is
suspected on a small number of southern NSW farms.
One recorded case in Australia (“Lawes” strain – goats,
Queensland).
Resistance in Haemonchus is common in northern NSW & S.E.
Queensland. One strain also ML-resistant.
Small number of resistant strains of liver fluke in Australia .
Small number of resistant strains of liver fluke in Australia
(Goulburn Valley, Victoria).
It is commonly believed that drench resistance is
only a problem of the higher rainfall sheep
raising areas of Australia.
More frequent
drenching is required in these areas and this,
combined
with
occasional
under-dosing,
produces greater selection for resistance in
worm populations. However, there is evidence
that drench resistance in western NSW may be
more prevalent than previously realised,
especially given the Western Australian
experience suggesting that selection for
resistance is stronger in dry environments (see
below).
A Western Australian perspective
Resistance to anthelmintics affects virtually all
Western Australian sheep farms, and is believed
by Dr Brown Besier, Agriculture Western
Australia, to reflect the heavy selection pressure
favouring resistant worms, which survive in
sheep after summer drenching.
In environments where no or very few larvae
survive on pastures over summer, any resistant
worms remaining in sheep after summer
drenching are the main source of future worm
populations. Although the number of resistant
worms is initially very low, they can increase in
proportion (to susceptible worms) very rapidly
Resistance to benzimidazoles and levamisole in
the major parasite genera, Trichostrongylus and
Ostertagia, is present on almost every farm.
These drench groups are now of minimal value
when used individually; test figures indicate their
effectiveness to be less than 60% on 85% (BZs)
and 63% (levamisole) of farms. Combination
BZ-LEV anthelmintics are more than 95%
effective in only about 25% of cases, but remain
useful as a tactical drench on most farms.
The use of naphthalophos with a BZ, LV or
combination BZ-LEV drenches has increased,
as other drenches fail. However, considerable
variability in efficacy has been shown in tests,
and poor results can occur. It is recommended
that naphthalophos be used only in combination
(except against Haemonchus), with an efficacy
test conducted soon after the time of use.
The number of confirmed cases of macrocyclic
lactone (ML) resistance in Ostertagia has
increased rapidly in Western Australia in recent
years.
The recommended test format
differentiates ML efficacy (> 95% effective at a
full recommended dose rate) from resistance
(effectiveness of ivermectin at a half dose rate).
On this basis, figures from 1999 showed ML
resistance in approximately 38% of tests, and
reduced efficacy at the full dose on 19% of
SCIPS – page 9
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
farms. ML resistance has not been detected in
Haemonchus or Trichostrongylus.
Closantel resistance in Haemonchus has not
been detected in Western Australia.
A South Australian Perspective
In a study conducted by Dr Ian Carmichael of
SARDI Livestock Systems, in collaboration with
private veterinarians, 70 Merino cross wethers
under quarantine were artificially infected with a
worm isolate from a farm where worm control
had collapsed despite repeated drenching with
moxidectin. Faecal egg counts and total worm
counts after treatment confirmed that the
animals carried a strain of Brown Stomach
Worm that was strongly resistant to ivermectin.
Low positive faecal egg counts in 4/10 sheep
drenched with moxidectin at normal dose rate
and moderate counts in 8/10 sheep drenched at
half dose rate confirmed developing resistance
to moxidectin. Two similar separate isolates
have since been confirmed experimentally and
others are currently being examined. Each of the
properties concerned had used moxidectin
consistently.
Strategies to identify the extent of the problem
and to evaluate sustainable worm management
practices in the presence of various levels of
macrocyclic lactone resistance are being
developed locally through a combination of field
and laboratory research supported by industry.
SCIPS – page 10
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
RESEARCH ON MACROCYCLIC LACTONE
RESISTANCE
Development of macrocyclic lactone
resistance
To understand the factors that influence
selection for avermectin/milbemycin (ML)
anthelmintic resistance it is necessary to
examine the impact of drug treatment,
particularly persistent drugs, on all phases of the
worm life cycle. Thus a study, funded by AWI,
was undertaken by Dr Robert Dobson and Ms
Liz Barnes, CSIRO Livestock Industries, to
determine the efficacy of various ML
anthelmintics against worms resident in sheep at
the time of treatment, against incoming larvae
(L3) post treatment, and against development of
eggs in faecal culture.
Homozygous and heterozygous (F1) MLresistant strains of Barbers Pole Worm
(Haemonchus contortus) were used to infect
sheep before or after treatment with ivermectin
(IVM) oral, IVM-capsule, moxidectin (MOX) oral
or MOX-injectable.
Total worm count and
quantitative larval culture were used to
determine efficacy against parasitic and freeliving stages, respectively. For IVM-capsules
selection for resistance was greatest for adult
and L3 stages. It was least selective for egg
and L1-L2 larval stages because residual IVM in
faeces was highly effective in preventing
resistant genotypes developing to L3. MOX was
least selective against adult worms as it was
highly effective against resistant genotypes.
MOX was similar to IVM-capsules in its capacity
to be highly selective for resistant L3 genotypes.
MOX showed some ability to prevent
development of eggs to L3 during its persistent
phase.
The results indicated no evidence of sex-linked
inheritance for IVM resistance.
Mean IVM
efficacies
against
homozygous
and
heterozygous resistant adult worms were not
different, and IVM-capsule efficacy against
incoming L3 was approximately 70% for all
resistant genotypes, consistent with a dominant
trait. MOX was highly effective against the adult
resistant strains and approximately 76%
effective against the incoming L3 regardless of
resistance-genotype, also consistent with a
dominant trait. Both drugs displayed an ability to
inhibit the development in faecal culture of
eggs/L1-2 from worms surviving ML treatment.
Genetics of avermectin resistance
Studies by Dr Leo Le Jambre, CSIRO Livestock
Industries, of the inheritance of avermectin
resistance (AVR) in H. contortus indicate that, in
contrast to BZ and LEV resistance, AVR, in this
species at least, is inherited as a completely
dominant trait and is not sex-linked. Inheritance
of AVR as a completely dominant trait indicates
that the progeny resulting from the mating of, for
example, a resistant female and susceptible
male will be 25% susceptible and 75% resistant.
At low resistance gene frequencies, a dominant
trait will result in the more rapid development of
resistance than if resistance were inherited as a
recessive or incompletely dominant trait. Hence,
it is expected that AVR in H. contortus will
evolve more quickly than even benzimidazole
(BZ) resistance under the same conditions.
Furthermore, increasing the dose of drug to
make the heterozygote susceptible is not an
option when dealing with dominant resistance
genes because heterozygous and homozygous
worms are equally resistant.
Two AVR strains of H. contortus were used to
investigate the propensity for a non-persistent
anthelmintic, ivermectin (IVM), and a persistent
anthelmintic, moxidectin (MOX) to select for
anthelmintic resistance. Dr Leo Le Jambre and
his research team investigated the response to
selection for anthelmintic resistance by resident
worms and by incoming larvae in adult sheep
and in lambs. In these studies the adult sheep
developed immunity to the trickle infection,
whereas the lambs did not. A major finding of
this research was that selection pressure for
AVR on resident worms was lower than that on
incoming larvae. Selection for AVR larvae in
lambs was greater by MOX because MOX
prevented re-infection after treatment.
In
susceptible animals such as lambs, when the
anthelmintic was IVM, the resistant worms
remaining after treatment were soon again in the
minority because of re-infection involving a very
small proportion of resistant larvae. With MOX,
the resistant worms enjoyed a considerable
period of advantage because of its persistency,
which increased the period of selection for AVR
larvae and as a consequence resistant worms
remained in the majority for the period of
residual activity. Nevertheless, even with the
short-acting IVM, some selection for AVR larvae
was apparent.
Use of a persistent drug such as MOX increases
the chance of matings of resistant male with
resistant female worms, providing an opportunity
for genetic recombination among resistant
worms to develop the next stage of ML
resistance. Subsequent computer modelling of
Haemonchus contortus populations in a winter
rainfall environment where Closantel is used in
conjunction with broad spectrum anthelmintics,
predicted that IVM capsules would select most
rapidly for ML resistance. In the presence on
SCIPS – page 11
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
Closantel
resistance
MOX
would
be
intermediate, and IVM oral would be least
selective, however, if resistance to Closantel
were absent, then MOX would least selective.
SCIPS – page 12
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
SCOURING IN SHEEP
Diarrhoea resulting from increased water
content of the faeces leads to soiling of the
breech wool, commonly referred to as “dags”.
The major problems associated with dags are
increased incidence of breech flystrike and loss
of value of crutch wool. Dr John Larsen, of the
University of Melbourne estimates the cost of
sheep dags in the high rainfall region of Victoria
at $10 million per annum, and this is likely to be
an underestimate during periods of high wool
prices. Similar estimates have been made for
the high rainfall region of Western Australia.
Scouring is an important issue to sheep
producers, particularly Merino producers, in both
winter and summer rainfall regions.
The
causative factors of scouring differ between the
two rainfall regions. In winter rainfall regions
scouring is of two types: that associated with
large infections of gastro-intestinal parasites and
that due to hypersensitivity-type responses.
Hypersensitivity-type responses are unrelated to
level of infection and occur most commonly
during late winter to early spring when pastoral
conditions favour rapidly growing green
herbage. In summer rainfall regions scouring is
primarily caused by large infections of non-blood
feeding gastro-intestinal parasites. In contrast,
infections with the blood feeder, H. contortus,
result in the production of hard faecal pellets. Of
the two types of scouring, hypersensitivity
scouring is of most concern, as the causative
factors are yet to be fully identified making
management to minimise scouring problematic.
programs for increased resistance to worms are
unlikely to result in reduced incidence of
scouring. In fact, estimates from New Zealand
and those calculated by Dr Johan Greeff and
Dr John Karlsson, Agriculture Western
Australia, suggest that scouring may slightly
increase as a correlated response to selection
for increased worm resistance.
If this is
confirmed, sheep breeders would need to
include both worm resistance and dags in a
selection index to ensure against any potentially
undesirable genetic correlations. This issue is
the subject of current research funded by AWI
as part of the SCIPS program.
Genetic
correlations of dags with other production traits
have generally been found to be in a favourable
direction.
It is likely that undefined factors in green pasture
may be minor contributors to hypersensitivity
scours; ryegrass endophytes may be one such
factor. It has also been suggested that the high
levels of soluble sugars in rapidly growing
pastures have the potential to cause hindgut
acidosis, which would increase the water
content of faeces.
Because hypersensitivity scouring may occur
even at low levels of larval contamination on
pasture, traditional worm control options are
unlikely to be successful in its control. However,
Dr John Larsen has demonstrated that
treatment of ewes with controlled release
benzimidazole (BZ) capsules can greatly reduce
the incidence of severe dag but is unlikely to be
cost effective for this purpose alone.
Research conducted by Dr John Larsen has
demonstrated that in unselected sheep flocks
susceptibility to scouring, as measured by dag
score and dag weight, is highly repeatable
(repeatability 0.41 – 0.61) between years
demonstrating that selection against dags is
possible. Importantly, susceptibility to scouring
and to worms were found to be unrelated, but in
those sheep susceptible to scouring, ingestion of
even low numbers of infective larvae induced
diarrhoea.
No differences existed between
scouring susceptible (SS) and resistant sheep in
protective immune response to infection, but
during infection SS sheep had an increased
number of eosinophils in the upper regions of
the small intestine and changes to cytokine
profiles.
Treatment of ewes with controlled
release benzimidazole (BZ) capsules has been
demonstrated to greatly reduce the incidence of
severe dag, indicating L3 or L4 as the likely
source of worm antigen-initiated hypersensitivity
responses.
Because hypersensitivity scouring is unrelated
to susceptibility to infection, genetic selection
SCIPS – page 13
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
PARTIAL FLOCK DRENCHING TO MINIMISE
SELECTION FOR DRENCH RESISTANCE
survival, these strategies, with the potential for
lost production, may not be necessary.
The rapid increase in macrocyclic lactone (ML)
resistance in Western Australia indicates an
urgent need to review the “summer drenching”
worm control program, to reduce the selection
pressure for resistance in some environments.
A number of field trials in WA conducted by Dr
Brown Besier, Agriculture Western Australia,
have compared the effects of traditional summer
drenching with those of a modified program that
aimed to ensure the survival of some nonresistant worms in sheep over summer. In each
trial, either all weaner sheep in a flock were
drenched with ivermectin as they went onto crop
stubble in early summer, or a proportion of the
flock were left undrenched, to provide a flock
average worm egg count of 50 eggs per gram.
Two findings consistently emerged from the trial.
First, significant worm problems in winter were
associated with the part-flock drenching
strategy. Even low levels of autumn pasture
contamination with worm larvae led to high
worm burdens, high prevalence of scouring, and
significant production losses.
The summer
drenched sheep suffered no subsequent
parasite problems, and maintained good
production. Second, the level of drench
resistance in Ostertagia increased significantly
in the standard summer drenched flock, but did
not change from the initial level when some nonresistant worms were retained by partial flock
drenching over summer.
The trials indicate that “resistance dilution”
strategies
can
effectively
reduce
the
development of drench resistance, although
careful management is necessary to avoid a
significant production penalty.
Some possible “resistance dilution” strategies
include:
• Leaving a small part of the flock undrenched
over summer
• Leaving all the flock undrenched, if mean
worm counts are low (most likely in adult
flocks)
• Running some undrenched adult sheep with
weaners to provide non-resistant worms.
Frequent monitoring of worm egg counts will be
essential to ensure acceptable worm control.
Tactical drenching, or preferably, a move to a
less-contaminated paddock, may be advisable
to keep autumn pasture contamination at a low
level. Importantly, the need to modify summer
drenching will depend on the environment;
where there is substantial over-summer larval
SCIPS – page 14
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
“SMART GRAZING”
Recently, Dr Paul Niven, Dr Norman
Anderson and Dr Andrew Vizard, University of
Melbourne, have developed and trialed a worm
management system for winter rainfall areas
that combines strategic drenching with rotational
grazing over summer to reduce worm
contamination of pasture for weaners during the
following autumn.
In the winter rainfall regions of Australia
summers are generally hot and dry and the
majority of worm larvae, at this time, are found
inside the animal as opposed to on pasture (the
reverse of what is commonly seen in summer
rainfall regions). To capitalise on this situation,
the two summer drenching program has been
developed. The first drench is given at the start
of summer and the second towards the end of
summer. This program has been effective at
reducing worm contamination of pastures during
the following autumn because drenching
coincides with the time when most of the worms
are found inside the animal, thus resulting in the
death of the majority of the worm population,
and conditions on pasture are inhospitable for
egg hatch and survival of larvae, thus minimising
re-infection.
However, summer rains can lessen the
effectiveness of the two summer drenching
program by allowing egg hatch, larval
development and re-infection of grazing sheep,
resulting in greater deposition of worm eggs on
pasture. “Smart Grazing” aims to prevent the
loss of effectiveness caused by summer rains
and to reduce pasture contamination.
To
achieve this, dry sheep are grazed at two to
three times normal stocking rates for one month
after each summer drench. The paddock is
destocked during the intervening period and
average summer stocking rates are unchanged.
Early results have demonstrated that weaners
grazed on pastures prepared by “Smart Grazing”
had reduced worm egg counts during the
following autumn, winter and spring, peaking at
400epg compared to 250epg in controls. The
weaners involved cut 1.93kg of 16.8 micron
clean wool/head, compared to 1.75kg of 16.3
micron. The “Smart Grazed” weaners were also
2 kg heavier by the middle of the following
spring. Further results are expected shortly from
work
conducted
during
2000
on
five
demonstration/evaluation sites, in Victoria,
South Australia, New South Wales and
Tasmania.
SCIPS – page 15
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
EFFECTS OF NUTRITION ON RESISTANCE TO
INFECTION
Inadequate nutrition and gastro-intestinal
nematode parasitism are major constraints to
livestock production. The primary effects of
worm infections, apart from high levels of
mortality during severe outbreaks, are to reduce
feed intake, to increase loss of host protein by
leakage into the gastro-intestinal tract, and to
increase the requirement of the gastro-intestinal
tract for protein at the expense of muscle
growth.
These combined effects, even in
subclinical cases, may reduce production by as
much as 25-35% for weight gain, 10-25% for
wool growth and 20-30% for milk production.
However, the nutrition of the animal strongly
influences the magnitude to which infection
reduces production and also the extent to which
the animal can develop resistance to infection.
to those from uninfected sheep not receiving the
supplement. Of significance to the economic
feasibility of using nutrition as a worm control
option are the results of a trial conducted by Dr.
Frans Datta and Dr. John Nolan, University of
New England, that demonstrated beneficial
effects of protein supplementation on resistance
to infection, growth rate and wool growth for up
to 15 months after cessation of the period of
supplementation. Currently, Dr Lewis Kahn,
with financial support from ACIAR, is
investigating whether protein supplementation
will be a useful strategy to avoid production
losses while encouraging the acquisition of
immunity in weaner sheep to gastro-intestinal
parasites, and over what time period any
beneficial effects are expressed. Dr Malcolm
Knox is conducting similar trials with weaner
ewes to determine the effects of short-term
supplementation on immunity to infection, live
weight gain and reproductive performance.
Protein supplements
A large number of pen trials and a smaller
number of field trials have demonstrated that
animals supplemented with a source of rumenundegradable (i.e. bypass) protein have
increased resistance and resilience to gastrointestinal parasites. Increased supply of
digestible protein hastens the acquisition of
resistance, which allows animals to more rapidly
expel established worms.
Research from New Zealand has demonstrated
that an increased supply of rumen-undegradable
protein to young sheep and periparturient ewes
reduces FEC and worm burdens, whereas
increasing the supply of metabolisable energy
(ME) is ineffective.
When the supply of
digestible protein to young sheep infected with
T. colubriformis was increased by the addition of
60g crude protein (CP), worm burdens were
reduced by 65%. Similarly, when the supply of
digestible protein was increased to periparturient
ewes infected with T. colubriformis and O.
circumcincta, worm burdens shortly after
lambing were reduced by 87%.
Field trials conducted over two years by Dr
Lewis Kahn, University of New England and Dr
Malcolm Knox, CSIRO Livestock Industries,
have demonstrated that supplementation of
periparturient ewes with cottonseed meal (CSM)
for the six weeks immediately prior to lambing
lowered FEC.
Cottonseed meal typically
contains 36% CP of which about 50% is rumen
undegradable. Supplementation with 250 g/day
CSM reduced FEC by about 50% across both
years.
Increased protein and ME supply can increase
production of infected sheep to levels equivalent
Non-protein nitrogen supplements
When livestock are grazed on low quality
roughage the most critical nutritional deficiency
is often nitrogen. Provision of non-protein
nitrogen (NPN), such as urea, in the diet can
compensate for this deficiency and stimulate
feed intake, increase the supply of microbial
protein and improve feed utilisation.
Dr
Malcolm Knox, CSIRO Livestock Industries,
has demonstrated that NPN supplementation
(urea as 3% of total intake) to infected animals
on low-quality feed increases feed intake, live
weight gain and wool production with some
benefits
to
worm
resistance.
NPN
supplementation to infected animals on low
quality roughage can result in similar levels of
production to those from uninfected animals
without NPN supplementation.
Urea-molasses blocks (UMB), and dry licks
containing urea are popular low-cost means of
delivering NPN, energy and minerals. It is
suggested
that
low-cost
nutritional
supplementation with UMB or dry licks should be
included in integrated strategies for the control
of nematode parasites in areas or during times
of the year where low quality forages are the
predominant feed resource and the provision of
high quality protein supplements, rich in rumenundegradable
protein,
is
economically
prohibitive.
Trace elements
In addition to protein and energy, dietary
deficiencies or variables inhibiting the utilisation
of minerals can also limit the ability of the
immune system to deal with parasites. Trace
elements are components of enzymes and
SCIPS – page 16
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
therefore have pivotal roles in biochemical
reactions
that
can
have
widespread
repercussions in animal physiology. Increased
metabolic activity can induce clinical signs of
mineral deficiency in animals with sub-clinical
deficiency. Cells with a short half-life such as
lymphocytes are particularly sensitive to trace
element deficiency.
Theoretically, therefore,
deficiencies of most of the trace elements could
affect the development of protective immunity to
worms, but this is a relatively unexplored area.
Dr
Susan
McClure,
CSIRO
Livestock
Industries, has demonstrated that diets low in
Mo impede the ability of sheep to reject a
challenge infection of T. colubriformis, and other
researchers have shown similar effects with H.
contortus. The development of resistance to T.
colubriformis in housed 8-month-old Merino
weaners was assisted by a dietary intake of Mo
in the order of 0.15-0.30mg Mo/kg live weight,
provided
by
feeding
diets
containing
approximately 6-10mg Mo/kg DM. This appears
to have been an effect on the immune response
to initial exposure to T. colubriformis and was
associated with three- to five-fold decreases in
egg and worm counts after challenge. Mo may
enhance the inflammatory response to
nematodes either directly, or indirectly by
reducing the effectiveness of local Cudependent anti-inflammatory enzymes. Normal
pastures contain 0.5 to 3.0mg Mo/kg DM, which
is less than the optimal range for development of
resistance.
worms, and ninety others were kept worm free.
Within both groups 30 animals were given cobalt
bullets, 30 received a monthly injection of
vitamin B12 and 30 had no cobalt
supplementation. The weaners were grazed for
6 months on a cobalt deficient farm which had
been destocked of sheep for more than a year
and was considered to be "worm free". Cobalt
deficient lupins were supplied as a field
supplement. Monthly body weights of all animals
and plasma vitamin B12 levels of selected
animals were measured to assess cobalt status.
Standard fleece measurements of all animals
were done at the end of the trial. There were
clear detrimental effects of cobalt deficiency,
worm infection (despite worm levels being very
low) and a cobalt by worm interaction in the
parameters
measured.
There
were
no
differences between animals that received
cobalt by means of a bullet or by monthly
injection of vitamin B12.
A further study with a similar design is in
progress using heavier weaners with greater
worm burdens on a higher plane of nutrition.
Field trials of supplementation with Mo have not
yet been done. Further studies may indicate
that interactions with other minerals affect the
ideal range of Mo concentrations, and caution
will need to be exercised, as supplementation of
a diet already adequate in Mo or deficient in Cu
may result in toxicity, and the levels quoted
above
are
higher
than
maximal
recommendations for long-term feeding.
Cobalt deficiency can impair the immune
function of sheep and this may increase
vulnerability to infection with worms. Cobalt
deficient soils are found in many Australian
agricultural areas, including large areas of South
Australia. Only one field study to date has
attempted to examine the interaction between
cobalt nutrition and internal parasitism.
SARDI Livestock Systems Parasitology Group
(contact Dr Ian Carmichael) examined the
influence of cobalt deficiency on productivity in
grazing weaner sheep with a low nutritional
plane and sub-clinical worm burdens. Ninety
merino cross weaners were artificially infected
with a standard low dose of the commonest local
SCIPS – page 17
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
BREEDING WORM RESISTANT SHEEP
Worm resistant animals can be found in any
flock, whether they are in a wormy, high rainfall
environment or a dry area. Selecting for worm
resistant sheep is a gradual but permanent
approach to the sustainable control of internal
parasites.
Nemesis project
Resistance
to
internal
parasites
varies
considerably between animals and 20-30% of
this variation is due to genetic differences
between animals. Presently the largest source
of genetic variation in resistance is between
sheep within a flock, rather than between
different flocks. Therefore, it is unlikely that any
particular ram source (which has not been
selected for resistance for at least five to six
years) will be more resistant than any other.
The first step to incorporate resistance into a
breeding program is to carry out faecal sampling
of young rams to determine faecal egg counts
(FEC). The second step is to have the FEC
analysed to produce FEC Estimated Breeding
Values (EBV).
This is an important step
because this analysis removes variations in FEC
that may occur from year to year, and means
that sires tested in different years can be
genuinely compared.
Breeders can then
determine what emphasis they want to place on
breeding for resistance.
Modelling predictions indicate that it would take
10-12 years selection with a high emphasis on
breeding for worm resistance to be able to
eliminate one drench from the annual program.
Further reductions in drenches follow quickly,
and predictions are that after about 15 years
drenching could cease. These predictions are
supported by results from a CSIRO experimental
flock that has been selected for worm resistance
for about 20 years.
There are approximately 40 Merino breeders
(November 2000) across Australia who have
incorporated selection for worm resistance in
their breeding programs. The average length of
time for which these breeders have been
selecting for resistance is in the order of three to
five years, although some started their selection
programs as early as 1991.
The average
selection pressure on worm resistance is in the
range of 25-50% of the maximum achievable if
FEC were the only selection trait. This is less
than that used in modelling predictions, but any
reduction in FEC is going to play a significant
role in reducing pasture contamination and will
be a permanent step toward long-term worm
control.
As part of the SCIPS program, AWI is providing
support for a project to increase the adoption of
Nemesis by the Australian wool industry. The
project is led by Dr Sandra Eady, and is
supported by National Extension Officer, Ms
Emma Doyle, CSIRO Livestock Industries. The
objectives of the project are to standardise
testing and analysis procedures for FEC EBV, to
quantify the relative economic value of worm
resistance for different environments, and to
prepare and deliver support material for
breeders and ram buyers on applying Nemesis
technology.
A separate but complementary SCIPS project is
being conducted by the University of
Melbourne’s Mackinnon Project, led by Dr John
Larsen. The project team will be working with
leading commercial woolgrowers and stud
breeders to increase the availability of rams sold
with FEC EBV in Victoria. An initial survey of
1062 woolgrowers has identified 28 key studs
with the greatest influence on Victorian Merino
genetics, and these will be the target audience
for the project.
Genetic markers for parasite resistance
Selection for worm resistance currently requires
exposure of sheep to parasites either as a result
of natural infection from pasture or by artificial
challenge. One way to avoid the need for
parasite exposure is to use genetic markers
which allow detection of specific regions of DNA
in sheep which are associated with worm
resistance. The usefulness of genetic markers
depends initially on the genetic control of the
resistance trait and on the proximity of the
marker/s on the chromosome to the gene of
interest.
If the trait is due to the combined action of many
genes of small effect (polygenic) it is unlikely
that genetic markers will be useful in identifying
animals of very superior resistance status.
However, if resistance is due to the effect of a
single gene, or the actions of one or a few genes
of moderate or large effect (i.e. Quantitative Trait
Loci or QTL) the probability of identifying useful
markers is much greater.
Until recently the genetic control of resistance to
internal parasites of sheep was thought to be
mainly polygenic but recent mathematical
analysis of data from the “Golden Ram” H.
contortus resistant flock at the University of New
England (UNE) has indicated the presence of a
QTL for resistance. The “Golden Ram” flock,
currently being managed by a research team led
by Dr Steve Walkden-Brown, UNE, was
established in the early 1980s after the progeny
SCIPS – page 18
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
of about 60 Merino sires were screened for
resistance to H. contortus. The progeny of one
sire were found to be extremely resistant to H.
contortus with FEC some 4000 epg less than the
mean FEC for the other sire progeny groups.
This ram was subsequently referred to as the
“Golden Ram” and was used as the founder ram
for the “Golden Ram” Flock.
Recent analysis of nearly 15 years of pedigree
data, consisting of about 4400 Merino sheep
with 2500 records for FEC, indicated that
approximately one third of the genetic resistance
to H. contortus in these animals is attributable to
QTL. This analysis indicated that when animals
homozygous for the desirable QTL allele(s) were
compared to those without the QTL,
homozygous animals would have a FEC of
approximately 5000 epg lower (46% reduction)
at days 28-35 following challenge with 11,000
infective L3 H. contortus.
Because resistance in the “Golden Ram” flock
has been identified as being partly controlled by
a QTL the prospects for finding and eventually
using genetic markers for worm resistance are
good. During the last ten years, a very good
map of the sheep genome has been developed,
which now consists of well over 1000 genetic
markers.
Recently, Dr Ken Beh, CSIRO
Livestock Industries, has completed the first
stage of the search for genetic markers for
parasite resistance. These studies revealed six
chromosome regions of interest for further
analysis as the most likely genome regions to
carry parasite resistance genes. The final step
to developing useful markers as selection aids is
to correlate genetic differences in worm
resistance to FEC. Ultimately, a simple test
using blood or wool follicle samples will be
developed to enable breeders to select sheep
based on their genetic make-up.
While the identification of genetic markers close
to the genes contributing to parasite resistance
would assist in the selection of resistant animals,
it is not without problems. The major issue is
the need to confirm the association between the
genetic
markers
and
the
resistance
characteristic, FEC, in different populations and
generations. This is because recombination
events can disrupt the linkage between the
resistance QTL and the informative genetic
marker. This limitation can be overcome by fine
mapping of the actual gene(s) responsible,
which would result in a DNA test that would work
across populations without the need to reconfirm
links with the resistance characteristic.
Blood antibody levels – the use of the Host
Resistance Test
Measurement of antibody levels in blood has
been suggested as an alternative method to
FEC to assess the level of host resistance to
internal parasites and to provide the basis for
selection programs. The Host Resistance Test
(HRT), distributed through AgVax Developments
Ltd, NZ is a commercial kit for determining blood
antibody levels to T. colubriformis and to H.
contortus. Information provided with the HRT
suggests that the most appropriate time to
assess the antibody level of animals is from six
to eight months of age and that only one sample
per animal’s lifetime is required as the
repeatability of subsequent tests is very high.
Recently, Dr Betty Hall, Elders Technical
Services, has serially sampled 1200, 1999 drop
young rams from four Merino studs for blood
and FEC under a Producer Initiated Research
and Development project funded through AWI.
The aim of the project was to determine the
correlation between FEC and antibody levels
and the repeatability of these traits, under
Australian conditions.
FEC and species
differentiation were performed using routine
procedures, and antibody levels in blood to T.
colubriformis and H. contortus were determined
with the HRT.
Analysis of the data indicated the following:
• The repeatability of antibody level between
samples from the same sheep was
negligible at 0.02, indicating that one
measurement on its own provided almost no
information on subsequent samples.
• The repeatability of FEC between samples
from the same sheep was low at 0.2, which
is in agreement with published estimates but
substantially greater than for antibody level.
• The phenotypic correlation between FEC
and antibody level was very low at 0.07,
which indicates that the two traits are not
closely related.
• The
phenotypic
correlation
between
antibody levels to T. colubriformis and to H.
contortus was generally high at 0.70,
suggesting that both tests may be
measuring
the
same
common
trichostrongylid antigen or epitopes.
Relationship between resistance to worms
and lice
As with worms, control of sheep lice relies
almost exclusively on chemicals, The continued
use of external parasiticides is threatened by
resistance (especially in the case of synthetic
pyrethroids) but more immediatley, by rising
concerns over occupational health and safety
SCIPS – page 19
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
and the environmental impact of residues on
wool.
Dr Peter James and Dr Ian Carmichael of
SARDI Livestock Systems have recently
demonstrated significant phenotypic correlation
between resistance to lice and resistance to
both natural and artificial challenge with T.
vitrinus.
In addition, the immunological
mechanisms that mediate protection against
arthropods and helminth parasites appear to be
similar. If resistance to helminths and lice are
genetically related, by selecting for resistance to
internal parasites growers may also increase
resistance to lice, and in the longer term, reduce
the need for chemical treatments.
Further
studies are underway to assess the genetic
associations between resistance to lice and
resistance to internal parasites.
SCIPS – page 20
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
VACCINES
Over the past decade, several research groups,
usually funded within commercial collaborations,
have trialled both native antigens (harvested
from worms) and recombinant antigens
(synthesised
e.g.
by
bacteria)
from
Haemonchus, Trichostrongylus and Ostertagia
spp as vaccines. These antigens are of two
types: concealed antigens, which are not
normally
"seen";
and
conventional
or
excretory-secretory (ES) antigens that are
"seen" by the host immune system during
natural infection.
Research in this field has often been deemed
disappointing because control of internal
parasites with vaccines is not as high as the
level of control afforded by anthelmintics. Unlike
broad spectrum anthelmintics, any new worm
vaccine is likely to be effective for only one
species of parasite, so that the ultimate goal, a
multivalent worm vaccine, is most likely to be
achieved by combining several individual
vaccines – a prolonged process. There are
presently no commercial vaccines for any
gastro-intestinal worm parasite species of any
host.
However, worm vaccines would not have to
match the control level of anthelmintics to
provide substantial benefits. The benefits of
lower FEC would continue to accrue over
generations as larval numbers on pasture
declined. Moreover, some level of infection in
vaccinated animals would be advantageous in
allowing the development of natural immunity.
Modelling indicates that a conventional vaccine
producing a 60% reduction in worm numbers in
80% of the flock would provide better worm
control than standard drenching programs. The
equivalent level of control needed from a
concealed antigen vaccine is estimated to be
higher (80% reduction in 80% of the flock)
because natural exposure would not boost the
vaccine-induced immunity.
Worm vaccines based on concealed antigens
Concealed antigens are based on proteins that
have been isolated from the surface of the worm
intestine. When they are injected into a sheep,
its immune response is stimulated to make
antibodies, which circulate in the blood. These
antibodies are then ingested by the parasite and
adhere to the gut of the worm, blocking normal
digestive processes so that the parasite is
weakened, lays far fewer eggs and dies.
Research conducted by Dr Ed Munn, Babraham
Institute, UK and Dr David Smith, Moredun
Research Institute UK has demonstrated
impressive protection against blood sucking
worms (e.g. Haemonchus) using concealed
antigens, but not so far against the non blood
feeding worms (e.g. Ostertagia). Dr Munn's H11
antigen has been shown to be highly effective in
very young lambs, able to prevent the
periparturient egg rise in pregnant ewes, and
capable of protecting against multiple drug
resistant and geographically distant strains of
Haemonchus in a variety of sheep breeds.
Unfortunately it is not possible to cost-effectively
harvest these candidate vaccine proteins from
Haemonchus for use in a commercial product.
Attempts to synthesise recombinant antigens by
means of biotechnology have suffered problems,
mainly involving inability to induce expression of
the recombinant protein in the correct
conformation to generate an effective protective
response. However, once the protein is folded
correctly, the technology is already well-placed
for both the formulation and injection of vaccine
to produce high and sustained levels of
protective antibody as in the “Tickguard” vaccine
sold for controlling the cattle tick.
Dr Sue Newton's group at the Victorian Institute
of Animal Science (VIAS), Agriculture Victoria,
Attwood, is collaborating with Dr Munn with the
support of Novartis Animal Health in the
development of recombinant H11 vaccines.
VIAS and Novartis scientists have also been
engaged in a five year joint research program
recently renewed for a further three years to
develop novel recombinant worm vaccines. This
$2 million p.a. project is the largest in the world
on antiparasite vaccines for farm animals.
Unfortunately, current indications reveal no
sufficiently promising alternative approaches for
use of concealed antigen vaccines against the
non-blood feeding species, although this is a
subject of active research.
Worm vaccines
antigens
based
on
conventional
Generally,
vaccines
comprising
subunit
conventional antigens have not been able to
generate high levels of those protective
responses that are acquired following natural
infection. The high levels of protective immunity
following natural infection in adult sheep are
associated with an allergic-type response
(distinct from “scouring hypersensitivity”).
Recent research conducted by Dr David Emery,
CSIRO Livestock Industries with neonatal lambs
has indicated that trickle and “truncated”
infections more effectively immunise suckling
lambs than weaners against Trichostrongylus
and Haemonchus.
This effect may be
immunological (as a carryover of maternal
immunity) or nutritional, and may point the way
SCIPS – page 21
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
for a reassessment of immunity to worms.
Current research in this area is attempting to
produce cost-effective strategies for adoption by
industry, whether these involve nutritional or
immunological means.
Nevertheless, at
present, levels of protection achieved by
vaccines in pen trials are not sufficiently high to
justify their commercial release.
indicated that higher antibody levels were
associated with lower FEC.
These results
indicate that pregnant ewes on pasture can
respond to ILV but that the level of protection is
not sufficient to prevent disease.
Research led by Dr Els Meeusen at the Centre
for Animal Biotechnology, University of
Melbourne, has identified and isolated some of
the antigens involved in natural protection
against gastrointestinal nematodes and has
shown significant levels of protection can be
achieved after vaccinating sheep with a single
purified antigen from Haemonchus contortus.
Dr Wayne Hein and his group at AgResearch,
Wallaceville,
NZ,
are
concentrating
on
developing
vaccines
specifically
for
Trichostrongylus colubriformis.
Irradiated larval vaccine
Periparturient depression of immunity can lead
to high nematode FEC in ewes and
subsequently
result
in
heavy
larval
contamination on pasture, with the potential for
large worm burdens in their offspring. Dr Leo
Le Jambre and Mr Ian Lenane, CSIRO
Livestock Industries, and Mr John Macfarlane,
Armidale Rural Lands Protection Board,
postulated that by boosting immunity prior to
parturition by vaccination with an irradiated
larval vaccine (ILV), FEC could be lowered to a
safe level during the periparturient period.
Irradiated larvae have been exposed to a
prescribed level of radiation that effectively
renders them sterile and incapable of complete
development within the sheep.
While this
treatment removes the potential for severe
production losses, the host is nevertheless
exposed to a large dose of worms in order to
initiate an effective immune response.
Pregnant ewes at pasture on three collaborating
farms were vaccinated with both 10,000 H.
contortus and 20,000 T. colubriformis irradiated
larvae seven and three weeks before lambing.
Two weeks after the completion of lambing and
again three months after lambing, at weaning,
FEC and parasite-specific IgG antibody levels
were determined. Compared with ewes that had
not been vaccinated, FEC in vaccinated ewes
tended to be lower, with 35% and 15%
reductions in FEC at two weeks after lambing
and at weaning, respectively.
Mathematical
analysis found that there was a negative
correlation between FEC and circulating
antibody levels at both sampling periods after
lambing, with antibody levels accounting for 35%
of the variation in FEC. The negative correlation
SCIPS – page 22
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
BOOSTING IMMUNITY IN YOUNG LAMBS
Recent research by Dr David Emery and Dr
Susan McClure, CSIRO Livestock Industries,
questions the previously held assumption that
young lambs cannot develop immunity against
gastro-intestinal nematodes.
It has been
demonstrated that housed weaners (i.e. 4-6
months old) on an optimal diet develop good
immunity against T. colubriformis, being >80 %
protected after six weeks of a primary infection.
However, the primary infection needs to be
cured with anthelmintics as weaners do not
generally eliminate this first worm burden.
Unfortunately the situation in the field is more
complex and weaner Merino sheep commonly
remain susceptible to infection from T.
colubriformis until at least one year of age.
Exposure of lambs to infection will carry a
penalty in the form of lost production but once
immunity is firmly established, there appears to
be no adverse effect on production. Therefore,
the relative merits of immunity/independence of
anthelmintics and maximal growth rate need to
be evaluated.
For example, a prime lamb
enterprise may elect to use anthelmintics to cure
infection rather than host immunity to prevent it,
but a Merino enterprise may benefit in the
longer-term from methods to enhance immunity
prior to weaning.
Dr David Emery and Dr Susan McClure have
recently demonstrated that housed neonatal
lambs (i.e. birth-7 weeks old) also mount good
protective immune responses to T. colubriformis,
and moderate immunity to H. contortus, and
there is evidence that this protection is better
than that in older lambs.
Immunity to H.
contortus does not appear to develop as rapidly,
possibly because of its greater pathogenicity. In
pen trials, deliberate daily infection of neonates
and weaners with T. colubriformis eventually
resulted in an 80% reduction in worm burden in
the neonates, but only a 28% reduction in
weaners, compared with uninfected (control)
sheep, following challenge infection.
Worm
burdens of deliberately infected neonates were
80% lower than those of deliberately infected
weaners.
The high levels of protective
responses in neonates have been identified as
an allergic-type response and separate from
“scouring hypersensitivity”.
Thus, it should be possible for lambs to develop
immunity to some gastro-intestinal nematodes
by the time of weaning if the following principles
are applied:
• Lambs are exposed to worms – if lambing
ewes are drenched onto clean pasture,
lambs cannot be expected to become
immune.
• Predisposing factors (e.g. concurrent
disease, malnutrition and stress due to
climate, weaning, transport etc), which
impede the development of immunity, are
removed. Research suggests that good
nutrition is particularly important during the
induction of the primary immune response,
i.e. when lambs are first exposed to worms,
and during the early post-weaning period
when the developing immune responses are
competing with growth for a reduced amount
of available nutrients.
SCIPS – page 23
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
BIOLOGICAL CONTROL OF PARASITIC
NEMATODES
With the increasing problem of internal parasites
showing resistance to anthelmintic chemicals,
animal health practitioners are becoming acutely
aware of the need for alternative means of
control. Certain fungi show great potential as
biological control agents against the major
parasitic nematodes of livestock, and offer a nonchemotherapeutic means of controlling this
problem.
Biological control of internal parasites is targeted
at controlling the free-living stages of the worm
life cycle. Research by Dr Malcolm Knox,
CSIRO Livestock Industries has involved the
utilisation of several strains of nematodedestroying fungi, which have been shown to be
very effective in reducing populations of infective
stages of nematode parasites in contaminated
faecal material. These fungi reduce numbers of
worm larvae in faecal material by trapping and
destroying them in sticky nets, resulting in fewer
infective larvae on pastures.
Research in
Denmark and Australia has identified the fungus
Duddingtonia flagrans as the most promising
candidate for biological control. While there are
many (>100) species of nematode-destroying
fungi, those whose spores can survive passage
through the gastro-intestinal tract would be most
useful in livestock parasite control programs.
be delivered to animals through on-farm addition
to grain supplements, incorporation into lick
blocks or in a controlled-release device. These
delivery systems are most effective when spores
are kept dry prior to ingestion, since spores that
have already germinated have diminished
survival through the gastro-intestinal tract.
Perhaps the ultimate test for the effectiveness of
this method of biological control is whether
nematophagous fungi can control larval
emergence of H. contortus, which can occur in
very large numbers. Comparison of the efficacy
of this method of biological control against
current best practice strategic chemotherapy
under controlled pasture conditions at PRL
Armidale will then lead to larger scale on-farm
field testing on a national scale as part of
registration requirements.
European field trials have demonstrated that
pastures grazed by animals given fungal spores
may have up to 80% less infective larvae on
pasture and this can reduce by 80% the worm
burdens in sheep that subsequently graze these
pastures. Computer modelling indicates that
reductions in worm burdens of at least 75% over
a minimum of 60 days will provide a level of
worm control equivalent to that obtained with
programs of strategic drenching with effective
drenches. Environmental studies conducted by
Dr Malcolm Knox to determine the effects of
deployment of these fungi in faecal material on
improved pastures recorded no detectable
detrimental effects on soil nematode populations
or other microfauna. CSIRO field trials have
also established that fungal treatment of young
weaners in autumn resulted in lower faecal egg
counts and greater live weight gains over the
following winter and spring.
Current research by Dr Malcolm Knox and his
research team is progressing in conjunction with
a commercial partner to scale up production of
fungal material to commercial levels and to
develop delivery systems of fungal spores for
Australia’s sheep, beef, dairy, goat and horse
industries. It is possible that fungal spores may
SCIPS – page 24
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
COPPER OXIDE WIRE PARTICLES FOR
HAEMONCHUS CONTROL
Failure of anthelmintic chemicals to remove
resistant strains of nematode parasites is
emerging as a serious health threat to sheep
production in many areas of Australia. Recently
a “super-strain” of H. contortus, resistant to most
chemical groups including the avermectins, has
been confirmed in Northern NSW, and
chemotherapeutic options are now limited.
Alternative means of controlling H. contortus
need to be identified to enable sheep production
to continue in this area.
an extended period, and may offer producers a
supplementary
control
to
chemotherapy,
particularly in areas where anthelmintic
resistance is a problem and copper supplements
are nutritionally beneficial.
Schering-Plough
Animal Health has supported this research
project.
Copper oxide wire particles (COWP) are an
efficient and effective means of treating copper
deficiency in grazing livestock. After dosing, the
COWP move from the rumen with ingesta and
the needle-like particles lodge in the folds of the
sheep’s abomasum where the low pH induces
release of high concentrations of soluble copper,
which has an anthelmintic effect against
abomasal nematodes. The protective effects of
COWP remain for five to seven weeks after
administration. The length of protection appears
to be related to the time taken for the needle-like
particles lodged in the abomasum to dissolve,
and the localised areas of high copper
concentration to disappear.
Research in New Zealand demonstrated that
administration of 5g of COWP (i.e. two copper
bullets/pills) reduced establishment of H.
contortus and O. circumcincta by 95% and 55%,
respectively, with no effect on T. colubriformis.
Subsequent research indicated that 2.5g COWP
(i.e. one bullet/pill) can virtually eliminate both
established and incoming larvae of H. contortus
for the period during which the particles are
dissolving.
In field trials conducted by Dr
Malcolm Knox, CSIRO Livestock Industries, the
use of COWP did not eliminate all worms from
treated sheep, but did significantly lower
numbers to levels that did not produce clinical
disease for five to seven weeks after
administration. A subsequent AWI-funded PIRD
study in conjunction with the BundarraKingstown Farm Management Group, has
confirmed this finding in small groups of COWPtreated sheep within flocks.
Further studies are in progress by CSIRO
Livestock Industries, Armidale, to determine
whether whole flock COWP treatment can offer
improved control through lowering faecal egg
output and reducing larval availability on pasture
and hence overall worm populations in grazing
flocks. Strategic treatment with COWP appears
to have the potential to reduce Haemonchus
spp. establishment and egg laying capacity for
SCIPS – page 25
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
CONDENSED TANNINS TO ASSIST WORM
CONTROL
Condensed tannins (CT) are a component of the
polyphenols (complex organic molecules)
present in plants, and are found at greatest
concentrations in dicotyledons such as legumes.
Within the plant, CT are stored in vacuoles and
are released only after disruption of plant cells by
chewing. Condensed tannins bind with proteins
and reduce fermentation of forage proteins in the
rumen. As a consequence, CT associated with
various temperate legumes have the potential to
increase the supply of protein to the animal,
indirectly resulting in improvements to host
resistance and resilience to infection. However,
not all CT behave in this manner, for it appears
that CT from many plants remain bound to
protein throughout the gastro-intestinal tract and
are excreted in faeces, thus actually reducing the
supply of protein to the animal.
However,
because many CT-containing legumes are very
high in crude protein, these plants can support
high rates of growth, even when rates of
dissociation between protein and CT are low.
There are indications that consumption of some
CT-containing plants significantly reduces
infections of gastro-intestinal parasites in sheep.
In addition, there are also reports that inclusion
(5%) of crude CT extracts, such as Quebracho,
in the diet result in a reduced level of T.
colubriformis infection.
Because Quebracho
contains other organic compounds in addition to
CT it is not clear what fraction is active against
gastro-intestinal parasites.
Recent research
conducted by Dr Lewis Kahn, University of New
England, with the financial support of ACIAR,
investigated whether inclusion of the CTcontaining
legume
maku
lotus
(Lotus
pedunculatus cv. Maku, with about 6% CT) in
pastures could enhance resistance and
resilience of weaner Merino sheep to infection
from T. colubriformis.
This research
demonstrated that pastures in which green
herbage contained about 25% maku lotus did not
increase resistance nor resilience to T.
colubriformis infection in young sheep when
compared with pastures containing 40% white
clover (Trifolium repens cv. haifa).
Of all the CT-containing plants that have been
investigated for anthelmintic activity, sulla
(Hedysarum coronarium) appears to be most
promising.
Sulla is a short-lived perennial
herbaceous legume used in certain areas of NZ
as a forage crop, with typical crude protein and
CT levels of 21% and 7% respectively. New
Zealand researchers have demonstrated that
lambs grazing sulla and deliberately infected with
T. colubriformis did not show increased FEC,
whereas similarly treated lambs grazing lucerne
showed an increase in FEC from 200 epg to
1200 epg. Worm burdens in lambs that grazed
sulla were 58% lower than those that grazed
lucerne.
Condensed tannin extracts (i.e. chemical
extracts of CT from plants) may also be directly
toxic to gastro-intestinal parasites. In research
conducted at the University of New England (Dr
Lewis Kahn), CT extracts from a number of
woody plants were shown to reduce nematode
viability by up to 60% and lower the rate of
success with which nematode eggs developed
into infective larvae by 40-70%.
Further
research is being conducted to better understand
the role of CT in parasite control and to screen
CT-containing plants that may have potential for
use in integrated worm control programs.
SCIPS – page 26
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
ACKNOWLEDGMENTS
The interest, support and information generously supplied by the contributors to this document are
gratefully acknowledged; their names and contact details are listed in the Appendix. Australian Wool
Innovation Ltd commissioned and funded the preparation of this publication.
SCIPS – page 27
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
APPENDIX – CONTACT DETAILS FOR CONTRIBUTORS
Name
Dr. Norman
Organisation
University of Melbourne
Telephone no.
0397312225
Email address
Norman@melbpc.org.au
Dr. Ken Beh
CSIRO Livestock Industries
0298402941
Ken.Beh@li.csiro.au
Dr. Brown Besier
Agriculture Western Australia
0898928470
bbesier@agric.wa.gov
Dr. Ian Carmichael
SARDI Livestock Systems
0882077922
carmichael.ian@saugov.sa.gov.au
Dr. Ian Colditz
CSIRO Livestock Industries
0267761460
ian.colditz@li.csiro.au
Dr. Robert Dobson
CSIRO Livestock Industries
0298402971
Robert.Dobson@li.csiro.au
Ms. Emma Doyle
CSIRO Livestock Industries
0267761454
Emma.Doyle@li.csiro.au
Dr. Sandra Eady
CSIRO Livestock Industries
0267761394
Sandra.Eady@li.csiro.au
Dr. David Emery
CSIRO Livestock Industries
0298402950
David.Emery@li.csiro.au
Dr. Robin Gasser
University of Melbourne
0397312283
r.gasser@vet.unimelb.edu.au
Dr. Johann Greeff
Agriculture Western Australia
0898211755
Jgreeff@agric.wa.gov.au
Dr. Betty Hall
Elders Technical Services
0267727500
bhall@elders.com.au
Dr. Wayne Hein
AgResearch, NZ
+64 4 9221560
wayne.hein@agresearch.co.nz
Dr. Des Hennessy
CSIRO Livestock Industries
0298402960
Des.Hennessy@li.csiro.au
Dr. Lewis Kahn
University of New England
0267732997
lkahn2@metz.une.edu.au
Dr. Lewis Kahn
Agricultural Information and
0267711273
lkahn@bigpond.com
Anderson
Monitoring Services
Dr. Malcolm Knox
CSIRO Livestock Industries
0267761440
Malcolm.Knox@li.csiro.au
Dr. John Larsen
University of Melbourne
0397312337
J.larsen@vet.unimelb.edu.au
Dr. Leo Le Jambre
CSIRO Livestock Industries
0267761450
Leo.Lejambre@li.csiro.au
Dr. Stephen Love
NSW Agriculture
0267765000
Stephen.love@agric.nsw.gov.au
Dr. Susan McClure
CSIRO Livestock Industries
0298402964
Susan.McClure@li.csiro.au
Dr. Els Meeusen
University of Melbourne
0383447345
e.meeusen@vet.unimelb.edu.au
Dr. Sue Newton
Agriculture Victoria
0392174219
Sue.Newton@nre.vic.gov.au
Dr. John Nolan
University of New England
0267732605
jnolan@metz.une.edu.au
Dr. Dieter Palmer
Agriculture Western Australia
0893683674
Dpalmer@agric.wa.gov.au
Dr. Mark Sandeman
La Trobe University
0394792164
M.sandeman@latrobe.edu.au
SCIPS – page 28
A SUMMARY OF RECENT AND CURRENT RESEARCH ON CONTROL OF INTERNAL PARASITES OF SHEEP
Dr. David Smith
Moredun Research Institute,
smitd@mri.sari.ac.uk
United Kingdom
Dr John Steel
CSIRO Livestock Industries
0298402930
John.Steel@li.csiro.au
Dr. Steve Walkden-
University of New England
0267735152
swalkden@metz.une.edu.au
Livestock Industries Consultant
0267759122
dwatson@midcoast.com.au
Brown
Dr. Dennis Watson
SCIPS – page 29