Lecture 4 Implementing a Genetic Improvement Program

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Developing and Implementing A
Genetic Improvement Program
Ken Stalder
Professor and Extension Swine Specialist
Department of Animal Science
Iowa State University
Ames, IA 50011-3150
IOWA STATE UNIVERSITY
E-mail: [email protected]
Department of Animal Science
Components of Swine Performance
1. Genetic ability of the pig
2. Environment - nutrition, health, facilities,
management practices, etc.
Phenotype (Performance) = Genetics + Environment
IOWA STATE UNIVERSITY
Department of Animal Science
Goal of Genetics Program
Do not allow inferior genetics or the mating system to
limit production efficiency
 Identify
a better source if genetics is the limiting factor in
obtaining maximum production performance

Usually NOT the case
 Be
sure you are using the correct mating system that maximizes
performance
 Be



sure that herd health is not limiting performance
May require herd depopulation and repopulation with healthy superior
genetics
Be sure to understand the costs of this choice
If relocating operations, may be good time to update genetics and improve
health
IOWA STATE UNIVERSITY
Department of Animal Science
Genetic Resources Available

Genetic Supplier


Breeds or Lines


Choice of suppliers
Choose the lines that excel for the traits that are important in
your markets
Choice of individual animals within the population
(breed or line) of choice


Choose the animals that meet your selection criteria
The average of those you select compared to the entire group
of potential select animals = selection differential

Impact the rate of genetic progress
IOWA STATE UNIVERSITY
Department of Animal Science
Genetic Resources Available

Selection at the Nucleus (GGP), Multiplier (GP), and
Commercial (P) levels




Genetic improvement through selection is a slow tedious process
Be sure that selection is for the traits that are important in your
market
Keep your eye on the selection goals
Mating Systems



Use a mating systems that matches your management preference
Maximize heterosis
Make use of breed complementarity
IOWA STATE UNIVERSITY
Department of Animal Science
Structure of a Breeding System
Boars –
Semen
Nucleus(GGP)
Future –
Embryos
Multiplier (GP)
Commercial (P)
IOWA STATE UNIVERSITY
Department of Animal Science
Heritability

The proportion of total variance observed for a given trait that is
attributable to genetics or the genes of an individual within a
population.

Is always denoted by the symbol h2

Two ways to define heritability
1. Heritability in the broad sense
2. Heritability in the narrow sense

Heritability is specific to the population and the trait under
consideration.

If the genetic or environmental variance for the same trait differs
in two population then the h2 has to be different.
IOWA STATE UNIVERSITY
Department of Animal Science
Heritability
Heritability
V
V
A
A
2
=
h 
VA  VD  VI  VEP  VET
VP
define - proportion of phenotypic variation
that is due to additive gene effects
MOST IMPORTANT CONCEPT IN ANIMAL
BREEDING
IOWA STATE UNIVERSITY
Department of Animal Science
Heritability
Trait
Heritability
Number born alive (NBA)
.10
Number weaned (NW)
.05
Sow longevity (SPL)
.10 - .15
21 – day litter weight (LWT21)
.15
Days to 1152 kg (250 lb.) (D250)
.35
Feed efficiency (F:G and G:F)
.30
Backfat thickness (BF10)
.40
IOWA STATE UNIVERSITY
Department of Animal Science
Selection
 What
traits to include in your selection
program?
 Consideration

Choose the traits that economically impact the operation





Number born alive – is the salable item produced by the sow
21-day litter weight – is what a producers selling weaned pigs is
selling (minimum weight required to obtain full value
Days to market weight – how long the pig will stay in finishing
facilities and feed efficiency (daily maintenance requirements)
Backfat and loin muscle depth or area – determines percentage
lean in the carcass which is the salable product (meat) for
consumption
Is the trait measurable
IOWA STATE UNIVERSITY
Department of Animal Science
Selection

Artificial selection – selection based on criteria
established by breeders

Selection - allowing only certain individual to
reproduce

Is the way genetic improvement in a population occurs.



Use of individual performance records
Use of EPDs
Use of DNA genetic information



Identified genes
Anonymous markers
Etc.
IOWA STATE UNIVERSITY
Department of Animal Science
Features Necessary for Selection

Equal opportunity – No animals receive preferential
treatment.

Systematic measurement of all animals – example
measure backfat the same way, same location, at the
same weight on every animal.

Environmental adjustments – e.g. parity, season of
year, on test weight, etc.


NSIF adjustment factors:


δ2G / δ2G + δ2 E = h2
http://mark.asci.ncsu.edu/nsif/guidel/guidelines.htm
Use of records – does no good record data if you don’t
make use of it.
USE records to assist in making selection decisions.
IOWA STATE UNIVERSITY
Department of Animal Science
Selection
 What
traits to include in your selection
program?
 Consideration

Is the trait measurable

Can the traits be measured accurately and in a repeatable
fashion
Influences heritability and the rate at which the traits can be
improved.

Does the trait have sufficient variation – specifically genetic
variation to which selection can be practiced
No variation = no improvement in the trait.
IOWA STATE UNIVERSITY
Department of Animal Science
Relative Economic Value of Swine Traits
Trait
Unit
Phenotypic
Standard
Deviation
Value
per
Unit
Value per
Standard
Deviation
Relative
Economic
Value
NBA
Pig
2.5
28.28
70.7
-39.28
LW21
Lb.
16
0.53
8.48
-4.71
D250
Day
15.6
-0.2
-3.12
1.73
F/G
Lb.
0.25
-20
-5
2.78
ADG
Lb/Day
0.19
12
2.28
-1.27
BF
in
0.15
-12
-1.8
1.00
NW
Pig
2.4
38.6
92.64
-51.47
Lifetime Pigs
Weaned
Pig
6
12
72
-40.00
IOWA STATE UNIVERSITY
Department of Animal Science
STAGES - Swine Testing And Genetic Evaluation System

National Swine Registry (NSR)


Duroc, Hampshire, Landrace, Yorkshire
Include F1 (Landrace x Yorkshire) data to make maternal data more
accurate

Multi-trait animal model

Daily across-herd EPDs on association computer

Across-herd summaries published semi-annually

Breed specific variance components and adjustments

www.nationalswine.com
IOWA STATE UNIVERSITY
Department of Animal Science
Postweaning Data

Pigs scanned at or near 250 pounds (~115 kg)

Most ideally set this off-test weight at your ideal market
weight

Most breeders scan every 3-4 weeks

Boars, gilts, and barrows

Record weight, backfat, loin muscle area

Data sent to NSR office same day

Results returned to breeder next day
IOWA STATE UNIVERSITY
Department of Animal Science
STAGES Program Components

Records of ancestry (Pedigree)

Performance measurement program

EBV estimation program

Public access to the genetic rankings

Indexes to combine traits that economically
influence selection decisions
IOWA STATE UNIVERSITY
Department of Animal Science
Data Procedures

Litter data recorded in farrowing house






Pedigree information (sire and dam)
Date farrowed
Number born alive
Number after transfer (number allowed to nurse)
21-day litter weight
Data sent to NSR office when litter is
recorded
IOWA STATE UNIVERSITY
Department of Animal Science
IOWA STATE UNIVERSITY
Department of Animal Science
EPD - Predicts
the difference in performance of an
animal’s offspring relative to the performance
of progeny of an average sire or dam
IOWA STATE UNIVERSITY
Department of Animal Science
What Is An EPD?
 Actual
difference in performance a
producer can expect from future progeny of
a sire or dam, relative to the future progeny
of an average parent of the same breed or
line
IOWA STATE UNIVERSITY
Department of Animal Science
EPDs Are Expressed in Units of the Trait Measured:

Days/113 kg [250 lbs] (days)

Backfat (mm, inches)

Number Born Alive (no. pigs)

Litter Weight (kg, lbs.)

Intramuscular Fat (%)

Etc.
IOWA STATE UNIVERSITY
Department of Animal Science
Selection
 Identifying
 Once




the traits for selection
identified, how do you apply the selection?
Independent culling levels?
Selection index
What is a selection index?
It is a composite measure of the economic value of the
genetic merit of an individual (gilt or boar) for a given set of
performance traits, such as backfat, average daily gain,
etc., relative to the contemporary group of individuals being
scored. The ranking based on the index is the basis for
selection decisions.
IOWA STATE UNIVERSITY
Department of Animal Science
Selection

Types of indexes

Terminal Sire Index (TSI)





A bio-economic index that ranks
individuals for use in a terminal
crossbreeding system.
TSI includes only EPDs for postweaning traits.
It weights the EPDs for backfat,
days to 250 pounds, pounds of
lean, and feed/pound of gain
relative to their economic values.
Each point of TSI represents $1
for every 10 pigs marketed or 10
cents per pig produced by a
particular sire.
Used to select terminal sires
IOWA STATE UNIVERSITY
Department of Animal Science
TSI Example
 Value
is $.10/pig for each point
 Sire
A has TSI of 118
 Sire
B has TSI of 108
 Difference
 Sire
of 10 TSI index points
100 litters @ 9 pigs/litter
 10
index point difference X $.10/pig X 900
pigs = $900 favoring Boar A over Boar B
IOWA STATE UNIVERSITY
Department of Animal Science
Selection

Types of indexes

Sow Productivity Index (SPI)



A bio-economic index that ranks
individuals for reproductive traits.
SPI weights the EPDs for number
born alive, number weaned, and
litter weight relative to their
economic values.
Each point of SPI represents $1 per
litter produced by every daughter of
a sire.
IOWA STATE UNIVERSITY
Department of Animal Science
Selection

Types of indexes

Maternal Line Index (MLI)




An index for seedstock that is used to
produce replacement gilts for
crossbreeding programs.
MLI weights EPD's for both terminal and
maternal traits relative to their economic
values, placing approximately twice as
much emphasis on reproductive traits
relative to post- weaning traits
Each point of MLI represents $1 per litter
produces by every daughter of a sire.
Use to select maternal sires and to cull
sows
IOWA STATE UNIVERSITY
Department of Animal Science
Selection
 Types


of indexes
Ideally idexes should be developed based on the economic
situation in your country.
Country specific indexes
IOWA STATE UNIVERSITY
Department of Animal Science
Selection

Once indexes are calculated and you have identified
the animals with acceptable breeding value indexes,
what other selection methods are needed?


Major genes



Stress gene (HAL)
Napole gene (RN-)
Candidate genes



Molecular marker tools
Estrogen receptor gene (ESR)
MC4R influencing both growth rate and feed efficiency
Mapped genes

PRKAG3 & CAST both genes influence meat quality
IOWA STATE UNIVERSITY
Department of Animal Science
Use of HAL and RN- markers

Breeders have tested for these markers world wide.

Several million tests run –

HAL nearly removed from all lines

RN- still exists in mostly Hampshires
Recommendation: Test and remove bad
(undesirable) alleles
IOWA STATE UNIVERSITY
Department of Animal Science
Selection

Once indexes are calculated and you have identified
the animals with acceptable breeding value indexes,
what other selection methods are needed?

Phenotypic selection




Feet and leg evaluation on boars and gilts
Genitalia evaluation on all boars and gilts
Underline evaluation on maternal line boars and gilts
Replacement boars and gilts might have the very best numbers but
may have feet and leg soundness or other issues that make it
difficult or impossible for them to breed.

From a genetic improvement standpoint they have no value
IOWA STATE UNIVERSITY
Department of Animal Science
Selection

Typically, phenotypic traits are selected upon by employing
Independent Culling Levels type of selection

What is independent culling?

Selection method in which minimum acceptable phenotypic level
is assigned to a trait being evaluated.

Selection of culling based on pigs meeting specific levels of
performance for each trait included in the breeder's selection
program.

Example


After you have established that any gilt meeting a Maternal Line Index
score of 95 and have found that 60 out of 100 gilts meet this value you
then proceed to score feet and leg soundness.
Score leg soundness in a group of breeding gilts on a scale of 1 to 10 with
10 being best. You keep anything that scores a 6 and above.
IOWA STATE UNIVERSITY
Department of Animal Science
IOWA STATE UNIVERSITY
Department of Animal Science
Selection of Crossbred Gilts
 Select
at a weight of 175 – 240 lbs
 Faster
growing gilts - better appetites
 Structurally





sound
Level designed, loose structured
Large feet with equal toe size
Wide chest, spring of rib (not flat sided)
Flexible joints, particularly pasterns on both front and rear
legs
No swollen joints
IOWA STATE UNIVERSITY
Department of Animal Science
Selection of Crossbred Gilts
 Underlines



Small, evenly spaced, well defined nipples
No inverted teats
No blind or infantile teats
 Backfat---0.60-0.80
in. is ideal
 Favor
docile, calm gilts over those that are
excitable and difficult to handle
IOWA STATE UNIVERSITY
Department of Animal Science
Incidence of failure to breed, lameness and culling for old
Cumulated percentage of culled sows
age, in the sows according to litter parity
Dagorn & Aumaitre, 1978
100
90
80
70
60
50
40
30
20
10
0
1
2
3
4
5
6
7
8
9
Number of litters per sow
Failure to breed
Lameness
IOWA STATE UNIVERSITY
Department of Animal Science
Old Age
Other
10
>10
Phenotypic evaluation

Indirect Selection for
Longevity

Buck kneed fore legs were
shown to be negatively
associated with:




Age at first farrowing,
Farrowing interval,
Total number born, and
Piglet mortality from birth to
weaning
Serenius et al. 2004.
IOWA STATE UNIVERSITY
Department of Animal Science
Phenotypic evaluation

Indirect Selection for
Longevity

Feet and leg evaluation

Conditions shown to
negatively impact sow
longevity


Buck-kneed front legs
Straight rear pasterns
IOWA STATE UNIVERSITY
Department of Animal Science
Phenotypic selection

Indirect Selection for Longevity

Conditions shown to positively
impact sow longevity

Weak front pasterns
IOWA STATE UNIVERSITY
Department of Animal Science
Phenotypic selection

Many thought that we could just breed
by the numbers

Phenotypic selection

Independent culling levels

Do impact traits that influence
profitability

Keep your best sows in the herd for a
long time

Impact fitness

Role with animal well being
IOWA STATE UNIVERSITY
Department of Animal Science
Selection for Sow Longevity

Generally not been a large focus directly at the
nucleus level

Trait is measured at the end of productive life

Trait in direct conflict with making rapid genetic
change

Selection pressure, if any is placed, is directed at
indicator traits affecting sow longevity



Feet and leg soundness
Backfat
Other conformation traits
IOWA STATE UNIVERSITY
Department of Animal Science
Crossbreeding Effects on Sow Longevity

Mean age and number of litters produced were lower in
purebred Yorkshire sows when compared to crossbred
sows (Jorgensen, 2000)


Purebred sows had higher culling for locomotion and
reproductive failure
Crossbreds averaged 3.61 parities at culling while the
purebreds averaged only 3.01 (Sehested and Schjerve,
1996)
IOWA STATE UNIVERSITY
Department of Animal Science
Mating Systems
– used at the nucleus level &
some level at multiplication*
 Purebreeding



Inbreeding
Linebreeding
Outcrossing
IOWA STATE UNIVERSITY
Department of Animal Science
Mating Systems
– used at the multiplication
level and at the commercial level
 Crossbreeding



Static Systems
Rotational Systems
Static Rotational Systems

System choice is dependent on:
1.
2.
3.
4.

Health of herd
Management level
Cost
Other
System goal = maximize heterosis or hybrid vigor
IOWA STATE UNIVERSITY
Department of Animal Science
Hybrid Vigor or Heterosis

The average performance of the offspring compared to the average
performance of its parents

Example average daily gain
Line A = 800 g / d
Line B = 800 g / d
Parental average = 800 g / d
Group of progeny from these parents average daily gain = 950 g / d
Hybrid vigor = 950 – 800 = 150 / 800 = 18.8%

Why maximize heterosis?

It is FREE producers are wasting money if you do not take
advantage of it.
IOWA STATE UNIVERSITY
Department of Animal Science
Hybrid Vigor or Heterosis
 Why


It is FREE producers are wasting money if you do not
take advantage of it.
It has its effects on those traits that involve fitness that
typically influence profitability the most





maximize heterosis?
Conception rates – does a sow become bred or not
Number born and number born alive – limits the number of pigs
that will eventually be sold
Longevity – how long the sow remains in the breeding herd
Etc.
Make sure the mating system of choice is implemented
correctly 100% of the time.
IOWA STATE UNIVERSITY
Department of Animal Science
Breed Complementarity
 No
breed of pigs is perfect or ideal for all traits
 Crossbreeding
allows the opportunity to mix
breeds to create a breed mix that is more ideal
than any of the parent breeds would have
been.
 Ideally,
a crossbreeding plan would mix breeds
that complement each other;

The strong points of one breed may offset the weaker
characteristics of another, resulting in more complete,
problem-free pigs.
IOWA STATE UNIVERSITY
Department of Animal Science
Breed Complementarity
Breed
Traits Excelling
Berkshire
Meat quality
Chester White
Number born alive, meat quality
Duroc
Growth, meat quality, lean growth
Hampshire
Carcass cutability
Landrace
Milking ability, number born alive
Meishan
Number born alive, thrifty piglets at birth
Pietrain
Carcass cutability (lean and heavy muscled) % lean
Poland China
Boar libido
Spotted
Boar libido
Yorkshire
Number born alive, growth rate
IOWA STATE UNIVERSITY
Department of Animal Science
Compensatory mating
 Mating
of individual animals to correct
problems in one animal by mating it to an
animal that excels in that area

Examples:


A sow might be slightly buck kneed so you might consider
mating it to a boar that has exception set to the knee so to
produce offspring that have near ideal set to the front leg
A sow might have a little too much fat so you consider mating to
a sire that is leaner than average so to produce offspring that
are near ideal for backfat.
IOWA STATE UNIVERSITY
Department of Animal Science
Types of Heterosis
1.
Individual heterosis –


2.
Maternal heterosis

3.
Most common heterosis discussed
Impacts the terminal offspring, the largest group of
pigs on a commercial pork operation.
Impacts maternal traits for both the sow and her
offspring
Paternal heterosis

Impacts the boar or terminal sire and has little if any
impact on offspring
IOWA STATE UNIVERSITY
Department of Animal Science
Types of Heterosis
1.
Individual

Advantage of a crossbred offspring over purebred
parents
IOWA STATE UNIVERSITY
Department of Animal Science
Types of Heterosis
2.
Maternal

Advantage of a crossbred mother over a purebred
mother

Advantage for the sow
Impact on the sow
Greater number of eggs ovulated
Greater conception rate
Greater farrowing rate

Advantage for the piglet
Heavier weaning weights
Number weaned
Primarily due to mothering ability
IOWA STATE UNIVERSITY
Department of Animal Science
Photo courtesy A.K. Johnson
Types of Heterosis
3.
Paternal

Advantage of a crossbred father over a purebred
father
Sperm production
 Semen volume
 Libido
Not as important as maternal heterosis

IOWA STATE UNIVERSITY
Department of Animal Science
Heterosis

Order of importance to maximize
1. Individual Heterosis –


Impacts the greatest number of animals and hence the
greatest profit potential
Largest number of traits likely influenced to some degree
2. Maternal Heterosis –



Influences both the sow and the piglet
Impacts a large portion of the breeding herd
Can have a great impact on profitability
3. Paternal Heterosis –


Typically only influence the boar itself
Least amount of profit gained if used for the paternal traits
influence by heterosis
IOWA STATE UNIVERSITY
Department of Animal Science
Relationship between heterosis and heritability
Traits
Heritability
Heterosis
Reproductive
Low
High
Health
Low
High
Growth
Moderate
Moderate
Carcass
High
Low
IOWA STATE UNIVERSITY
Department of Animal Science
Using Heterosis

Disadvantage


Superior performance observed in crossbred individuals is not
transmitted upon mating
Gene combinations are not transmitted to progeny



Only individual genes are transmitted to progeny
Additive gene action = heritability, EPDs, EBVs
Gene combinations are rearranged or lost when crossbred
animals are mated together

Random segregation of alleles during meiosis
IOWA STATE UNIVERSITY
Department of Animal Science
Genomic Selection

Genomic selection actually just extends our current approach to
selection.

Enhancing these proven methods by using more information to
calculate EPDs.

Genomic selection does not eliminate the need to have good data
on important families and individuals within our populations.

Genomic selection is selection based on actual DNA sequences
where the variation in DNA sequences among individuals is used,
along with pedigree and individual performance data, to predict
the EPDs for individuals with increased accuracy.

In the future we may be able to predict the value of combinations
of genes and their interaction.

Ultimately yielding more accurate predictions and faster rates of
genetic progress
IOWA STATE UNIVERSITY
Department of Animal Science
Example of a Terminal Crossbreeding program
(purchase all replacements)
Must find a producer that will make the Yorkshire x Landrace crossbred replacement
gilts.
Advantage: easy to manage, all matings are the same
Disadvantage: difficulty finding animals and the desired cross for the program
Pietrain
Or Duroc, or P X D
Live animals or semen
X
Y x L Female
100% Maternal Heterosis
Market Hogs
Market Hogs
100% Individual Heterosis
In the terminal offspring
IOWA STATE UNIVERSITY
Department of Animal Science
Example of an Internal Multiplication program for
a Terminal Crossbreeding program
Yorkshire
Landrace
X
15% of herd
Pietrain, Hampshire
Or Duroc, or P X D, H X D
X
Y x L Female
100% Maternal Heterosis
85% of herd
Market Hogs
Market Hogs
100% Individual Heterosis
In the terminal offspring
IOWA STATE UNIVERSITY
Department of Animal Science
Other types of mating systems

Rotational

Roto-terminal

Choice of system is largely driven by how a producer wants to
source replacement gilts

Purchase


Trading out of pocket expense for ease of management and implementation of
mating system
Implement a terminal cross mating system
IOWA STATE UNIVERSITY
Department of Animal Science
Other types of mating systems

Rotational

Roto-terminal

Choice of system is largely driven by how a producer wants to
source replacement gilts

Produce your own gilts – Internal multiplication program





Trading management ability for out of pocket expense (although cost of production is not
greatly different when all costs for raising your replacement gilts are actually totaled
Rotational mating system
Roto – terminal mating system
Use of boars or semen becomes a secondary choice in these systems
Producer needs more management when producing their own gilts
1. Genetic improvement (measuring growth, backfat, phenotypic evaluation, etc.)
2. Tracking animals through the production system
3. Properly sized internal multiplication system within your operation (Having sufficient number
throughout the year when needs vary i.e. seasonal breeding problems to deal with)
4. Computerized record keeping and genetic evaluation system really needed
5. Increased knowledge of workers (for example a person proficient in gilt selection is a must)
6. Production of maternal line barrows (typically less value that terminal market hogs)
7. Tracking specific sow matings (maternal line vs terminal line matings within the same system)
IOWA STATE UNIVERSITY
Department of Animal Science
Rotational crossbreeding system

Advantages:



Raise your own replacements so you control your genetic program
Entire herd devoted to terminal production, just retaining the best
gilts from the best mothers in the herd.
Disadvantage:


Do not take advantage of specialized sire and dam lines
Essentially all breeds utilized must excel at maternal (number born
alive, milking ability or 21-day litter weights), terminal (growth, feed
efficiency, etc.), and meat quality (pH, marbling, etc.) traits.



How many breeds or lines can really do this?
Requires the use of many breeds of boars in a given herd
Can be difficult to manage if numerous gilts from differing crosses
are maintained.
IOWA STATE UNIVERSITY
Department of Animal Science
Rotational Crossbreeding System
(2 Breed)
Yorkshire
The crossbred gilts are mated to
Yorkshire boars and those three
way cross gilt are then mated to
Landrace boars or semen. The
four-way cross gilts are mated to
Yorkshire boars or semen and so
forth.
Crossbred
females
Landrace
Crossbred
females
IOWA STATE UNIVERSITY
Department of Animal Science
Crossbred
Market hogs
All pigs
go to
market
Rotational Crossbreeding System
(3 Breed)
Landrace
Crossbred
females
Duroc
Crossbred
Market hogs
Crossbred
females
Crossbred
females
Yorkshire
IOWA STATE UNIVERSITY
Department of Animal Science
All pigs
go to
market
Rotational Crossbreeding System
(3 Breed)



In the three breed rotational crossbreeding system, the
three way crossbred gilt is mated to Berkshire boars and
those four way cross gilt are then mated to Chester White
boars or semen. The five way cross gilts are mated to
Duroc boars or semen and then finally we are back to the
six way cross gilts being mated to the original boar in the
order, the Berkshire boars or semen and so forth.
In all cases, replacement gilts are retained from the most
productive sows.
The order in which the boars are used does not matter but
once it is set must use the appropriate breed of boar on a
given sow


The sow herd could be made up of 3, 4, 5 and 6 way cross
females at any given time.
Each sow needs to be mated to the correct breed of boar to
ensure that the most heterosis possible is captured.
IOWA STATE UNIVERSITY
Department of Animal Science
Types of crossbreeding systems
 Rotaterminal
Crossbreeding system
IOWA STATE UNIVERSITY
Department of Animal Science
Rotaterminal crossbreeding system

Is a compromise between the terminal and rotational
system

Use rotational system to produce gilts and a terminal
system to produce offspring for market.

More heterosis realized than with rotational alone

Still can save replacement breeding stock


Still must buy terminal sire
Can select traits in individual breeds via the terminal
sire

Can focus on strengths and weaknesses of certain breeds
IOWA STATE UNIVERSITY
Department of Animal Science
Advantages of Rotaterminal System

Can purchase startup females once

Reduced health risk

Suitable for AI

Maternal heterosis is 86% (3-breed maternal cross) or
66.7% (2-breed maternal cross)

100% heterosis in market pig
IOWA STATE UNIVERSITY
Department of Animal Science
Rotaterminal Crossbreeding System
(2 Breed)
15% of herd –
Best sows
85% of herd –
Rest of sows
Terminal Boars =
Duroc, Pietrain, Hampshire, D x P, H X D
Yorkshire
Crossbred
females
X
Landrace
Crossbred
females
IOWA STATE UNIVERSITY
Department of Animal Science
Crossbred
females
All pigs
go to
market
Rotaterminal Crossbreeding System
(3 Breed)
15% of herd –
Best sows
85% of herd –
Rest of sows
Duroc
Boars
Landrace
Chester White
X
Crossbred
females
Crossbred
females
Crossbred
females
All pigs
go to
market
Crossbred
females
Maternal line barrows
go to market
Yorkshire
IOWA STATE UNIVERSITY
Department of Animal Science
Amount of heterosis capture in a rotational or
rotaterminal situation

The amount of individual heterosis and maternal
heterosis capture in the rotational crossbreeding
system is dependent on the number of breeds utilized.

In the rotaterminal situation, the same can be said
however, the loss of individual heterosis only applies
to the growth and performance associated with the
replacement gilts.


Most concerned with the maternal heterosis.
Remember in the rotaterminal system, 85% of the offspring attain
100% individual heterosis.
IOWA STATE UNIVERSITY
Department of Animal Science
Heterosis percentage in rotational crosses
Generation number
Crossbreeding
System
Equilibrium
1
2
3
4
5
6
2 breed rotation
100.0
50.0
75.0
62.5
68.9
67.2
66.7
3 breed rotation
100.0
100.0
75.0
87.5
87.5
84.4
85.7
4 breed rotation
100.0
100.0
100.0
87.5
93.8
93.8
93.3
5 breed rotation
100.0
100.0
100.0
100.0
93.8
96.9
96.8
6 breed rotation
100.0
100.0
100.0
100.0
100.0
96.9
98.4
IOWA STATE UNIVERSITY
Department of Animal Science
To calculate the number of replacement
gilts needed
Item
Example
Average Sow Inventory
(A)
2500
Annual Replacement Rate
(B)
.50
Number Needed / Year
A x B = (C)
1250
Number of Days in Isolation
(D)
60
Percent of Number Purchased that Farrow a Litter
(E)
.90
Time Needed to Clean Isolation Facility, Days
(F)
7
Number of Replacement Females to Purchase
Number of Replacement Female Groups
Number of Females Purchased per Group
IOWA STATE UNIVERSITY
Department of Animal Science
C / E = (G)
1389
365 days /
(D + F) = (H)
5.45
G/H
255
Replacement Gilt Needs

Assuming 1389 replacement gilts are needed annually
whether they are purchased or internally multiplied.

How many gilts will be required once selection takes
place?
Gilts needed for
Breeding Purposes
Percentage of Total Number of
Gilts Selected Gilts to Produce
1389
80%
1736
1389
65%
2137
1389
50%
3472
IOWA STATE UNIVERSITY
Department of Animal Science
Replacement Gilt Needs

Assume that 8 offspring reach market weight for each
grand-parent female in production in an internal gilt
multiplication system

Of the 8 offspring each grand-parent female produced
4 (one-half of offspring) are females and each female
has 2.2 litters per year (8.8)
Percentage of
Gilts Selected
Total Number of Grand-Parent
Gilts to
Sows Needed
(Assuming a 80%
Produce
farrowing rate of GP
females)
Percentage of Herd
Devoted to
Replacement Gilt
Production
80%
1736
246
9.8%
65%
2137
303
12.1%
50%
3472
494
19.8%
IOWA STATE UNIVERSITY
Department of Animal Science
Replacement Gilt Needs

Does not account for any disease outbreak, fluctuations in
farrowing rate (summer vs. other season)

Also must produce replacement grand-parent females

It is clear that the cost of producing the replacement gilt in an
internal multiplication system can vary quite easily
Grand-Parent
Sows Needed
(Assuming a 80% farrowing
rate of GP females)
Percentage of
Herd Devoted to
Replacement
Gilt Production
Grand-Parent
Females Needed to
Replace GP females
(Assumes 50% replacement and
75% conception)
Total number
of GP sows
and % of
herd
246
9.8%
75
321(12.8%)
303
12.1%
92
395 (15.8%)
494
19.8%
132
626 (25.0%)
IOWA STATE UNIVERSITY
Department of Animal Science
Thank you for your attention.
Are there any questions?
IOWA STATE UNIVERSITY
Department of Animal Science
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