ISRAEL JOURNAL OF
VETERINARY MEDICINE
THE ANALYSIS OF WEEKLY MILK BULK TANK COMPONENTS A
INDICATOR OF HERD HEALTH STATUS
Vol. 56 (2) 2001
T. Zadnik, M. Klinkon, M. Nemec and M. Mesaric
Clinic for Ruminants, Veterinary Faculty, University of Ljubljana, Cesta v Mestn
Ljubljana, Slovenia
Abstract
By measuring milk parameters such as Na, K, Cl, urea, enzymes LDH, betahydroxybutyrate (BHB), acetone, Somatic cell co
antibodies for enzootic bovine leukosis (EBL) in samples taken from the bulk tank provides a simple low cost method of asse
status of dairy herds. In 1998, we analyzed weekly bulk milk samples from 8 farms with 177 dairy cows. The levels of Na, K
LDH and SCC were sensitive indicators for subclinical mastitis. SCC of over 400.000 cell/ml in bulk milk tank was associate
(>24 mmol/L), Cl (>35 mmol/L) and high activity of LDH (>80 U/L), K concentration was decreased (<38 mmol/L). Positiv
and acetone in bulk milk samples were excellent parameters for identification of alimentary and production type ketosis. Hig
(>5,0 mmol/L) indicated an imbalance of energy, proteins and roughage in herd nutrition. Using bulk milk ELISA tests for E
individual Agar Gel Immunodiffusion (AGID) and ELISA tests gave negative results. Our results support the findings that bu
becoming the basic diagnostic material for herd health monitoring.
1 = negative* (-)
2 = positive ** (± to +++)
* = negative (-); ** = positive (±= 0,16 mmol/L; + 0,17 - 0,42 mmol/L; ++ = 0,43 - 1,72 mmol/L; +++ > 1,72 mmol/L)
The statistical model used was:
Yijklmn= µ + Li + Kj+ Sk + SCCl + Acm + eijklmn
where:
Yijklmn= observation resp. measured property ijklmn
µ
= mean value of observations
Li = influence of
farm (i= 1..8)
Kj = influence of husbandry (j= 1,2)
Sk = influence of ration with regard to season (k= 1,2)
k=1 from 1. to 17. and from 40. to 52 weeks of experiment
k=2 from to 18. to 39. week of experiment
SCCll = effect of SCC class (l= 1... 5)
Acm = effect of milk acetone concentration (m=1,2)
eijklmn = residual random error
3. Twice a year the bulk milk antibody tests used for enzootic bovine leukosis are based on ELISA (43). In this point we exam
single blood sample of all cows (n=177) from observed farms by ELISA and agar gel immunodiffusion test (43).
Results and Discussion
The main advantages of a bulk milk diagnostic test are that the sample is easy to obtain and the test is reasonably cheap, a
therefore be used as a routine indicator of subclinical diseases. This also yields data for use in epidemiological studies a
studying the genetic background of diseases. Pertinent parts of the milk profile outlined above have been used to stu
heritability of ketosis and mastitis (3). Bulk milk tests provide a good starting point for differential diagnosis, in additition t
value for blood serological monitoring. It is envisaged that veterinary practices could record the information from bulk mil
and incorporate it into preventive medicine programmes, particularly in relation to purchased animals (41). Regular testing o
milk samples every few months provides a simple low cost method of confirming continuing freedom from infection in k
disease-free herds; including those at potential risk of introducing new infection, and thereby allows opportunity for prompt
if indicated. For example, a positive result in a previously negative herd could herald an upsurge in infertility, abortions o
drop (1).
During a one year observation study we established a 35.2 % incidence of hypocalcemia with 4.5 % incidence of milk fever,
% incidence of hypophosphatemia, 23.5 % incidence of hyperketolaktia, 21.38 % incidence of clinical mastitis and 56
incidence of increased SCC (>400.000/ml) in individual milk samples. By bacteriological analysis of milk samples from clin
(n=57) and subclinically (n=81) infected cows (>400.000/ml) 57% S. aureus, 32% other streptococci, 6% E. coli, 4% S. agal
1% fungi and yeasts were detected. The average interval from calving to first insemination was 103.5±20.2 days.
Table 3 presents mean values of parameters analyzed in weekly bulk milk samples in regard to housing system, season, so
cell count, acetone content and the highest and respectively lowest average in 8 herds.
The one-year monitoring of somatic cell counts in weekly bulk milk revealed that the obtained average cell
493,000±122,124 sc/ml was too high. Namely, 44% of samples contained over 400,000 sc/ml. The results also demonstrate
from 8 monitored herds, two exhibited weekly elevated cell counts almost through the entire observation time.
On the basis of these findings we recommend that dairymen keep the somatic cell count in bulk milk below 250,000/ml.
concluded that a count exceeding 250,000 sc/ml indicated a majority of animals with udder inflammation (44).
Table 3 also demonstrates that an elevated cell count is closely related to higher LDH, Na, Cl and urea levels and that p
content decreases if somatic cell count increases. All these parameters were statistically significant with the exception of p
content which was insignificant (Table 4).
Within the framework of this work the acetone content in bulk milk was also determined on a weekly basis and 56 (13
positive responses were established. A detailed analysis has revealed that acetone was mainly due to feeding grass silage w
elevated butyric acid content, the so-called alimentary or false ketosis (5). Using the analysis of variance with 5 entr
calculated F-values and established statistical significance of individual factors affecting milk parameters. In Table 4 F-valu
individual influences and determination coefficients (R2) for milk content are presented.
The investigated milk properties in weekly samples were most significantly affected by the farm. This result is, we believe
objective because there are great differences among herds with regard to the management regime and health condition of
cows. Similar reports have been obtained by others (3,20,45). Season (temperature, humidity, husbandry) had also a sign
effect on the majority of parameters, especially on fat, proteins and urea levels as well as somatic cell count. Through July, A
and September the cell count was highest and the mastitis was most frequently observed (44). The authors reported that th
count was also affected, in addition to mastitis, by a whole range of factors, including the time of the year, and ensuing chan
feeding and husbandry (44,46).
The results confirm that the concentration of Na, Cl and LDH activity are closely related to somatic cell cou
increased cell count results in Na, Cl and LDH increases. This finding indicates that the results of the MLP-test sho
interpreted from various viewpoints. The most frequently established clinical state in cows is depressed milk secretion
mastitis. In such cases elevated cell counts (>350,000 sc/ml), elevated Na content (>23.00 mmol/L), Cl (>34.00 mmol/l and
activity (>80.00 U/L) were observed. Metabolic disorders in bulk milk samples associated with acetone content (ketolactia
less frequently detected. The concentration of protein and Na was markedly lower in bulk milk. Acetone appears in various
of ketosis with impaired metabolism of carbohydrates and lipids which is reflected at least at the initial stage in the compe
rumen with metabolic acidosis. The established acetone bulk milk Na content below 22.5 mmol/L as well as suppressed
secretion are sensitive indicators of metabolic disorders. Milk protein content is also decreased, whereas the somatic cell co
below 250,000 sc/ml. Similar findings have been reported by others who suggested the same milk parameters monitor
evaluation of the energy and fat metabolism in dairy cows (3,20,31,47,48).
In our statistical model we have identified a major part of the variance. Determination coefficient (R2) was highest
protein percentage and as much as 53.7% of variance was explained. Determination coefficients were rather high also b
concentrations (above 22.5%) with the exception of K (5.5%). Thus, the model encompasses the majority of factors signifi
affecting milk composition.
Up to 1987 there were no positive EBL reactors to our knowledge in Slovenia (49). All bulk milk and individual
samples were negative for EBL.
Table 3: Association of mean weekly ( n = 416) values of bulk milk parameters with housing and feeding, season,
health status, ketolactia and lowest and highest mean concentrations in 8 herds
Effects
n
Tied
312
Loose 104
Winter 232
Summer 184
SCC 1* 11
SCC 2* 14
SCC 3* 96
SCC 4* 267
SCC 5* 28
Acetone 360
(-)
Acetone 56
(+)
Min. **
Max
Total
416
Fat
%
4.15
4.32
4.21
4.31
4.09
4.18
4.20
4.19
4.21
4.18
Prot.
%
3.34
3.43
3.41
3.32
3.42
3.39
3.36
3.29
3.25
3.41
SCC
x 10003
Na
mmol/L
K
mmol/L
Cl
mmol/L
LDH
U/L
Urea
mmol/L_
421
702
441
512
77
178
319
532
1021
432
21.18
22.78
21.46
21.79
20.94
21.06
21.69
23.52
24.19
23.46
38.14
38.07
38.11
38.15
38.09
38.11
38.14
38.12
38.10
38.12
35.36
37.42
35.89
37.98
33.78
34.09
34.18
36.87
39.16
35.91
73.62
92.71
77.96
80.10
50.23
57.81
58.34
82.13
110.31
77.99
4.21
4.76
3.98_
5.52
3.93_
4.28
4.39
5.39
5.56
4.57
4.21
3.29
529
21.58
38.14
36.14
81.23
4.06
3.59
4.46
4.19
3.84
4.49
3.37
351
963
493
20.00
24.60
21.59
37.25
39.45
38.12
34.34
38.44
35.86
65.02 2.16
114.26 6.32
78.55 4.36
* 1 = up to 100,000 SC/ml
2 = 100,000 to 250,000 SC/m
3 = 250,000 to 400,000 SC/ml
4 = 400,000 to 750,000 SC/ml
5 = above 750,000 SC/ml
** = mean minimum and maximum value in herds
Table 4: Results of the analysis of variance with 5 entries, determination coefficients (R 2) and coefficient of variatio
Variability sources
Fat %
Prot. %
Cl mmol/L
Urea mmol/L Na mmol/L
K mmol/L
LDH U/L
Farm
***
***
***
***
***
NS
***
Housing system
**
*
*
NS
NS
NS
***
Season
*
***
***
***
NS
NS
NS
SCC - class
***
NS
***
*
**
NS
***
Ketolactia
NS
***
NS
NS
*
NS
NS
R2 (%)
36.0
53.7
32.2
27.4
22.5
5.5
23.2
CV (%)
6.8
3.7
2.1
25.5
10.8
2.7
29.6
*** = P < 0.001
** = P < 0.01
*
= P < 0.05
NS = insignificant
Conclusion
Losses from metabolic, mastitis and some endemic infectious diseases (IBR, BVD, Leptospirosis.) are often subclinical and
veterinary surgeons and farmers are unaware of the health status of their herds. Bulk milk tests offer an ideal opportun
improve this situation and stimulate an interest in monitoring herd health status, adopting appropriate control measures inc
vaccination and screening new stock. In future bulk milk antibody tests for Salmonella typhimurium and Neospora caninum w
introduced. Knowledge of herd health status is particularly relevant at present because many previously closed herds ar
purchasing replacements following of the cull for bovine spongiform encephalopathy. In some countries, bulk milk antibod
have provided a simple and convenient means of surveying the infectious disease status of their herds. On the basis of th
recent research we recommend for evaluation of the herd health status (metabolic, udder diseases) with bulk milk analysis w
following parameters: fat >3.85%, protein >3.17%, urea from 3.0 - 5.0 mmol/L, SCC <250,000/ml, Na >24.00 mmol/L, K >
mmol/L, Cl <35.00 mmol/L and LDH <55 U/L.
Acknowledgement
This work was made possible by the support of farmers and the Ministry of Science and Technology of Slovenia (Projec
5473 - 04505 - 97).
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