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 examined a single blood sample of all cows
(n=177) from observed farms by ELISA and agar gel immunodiffusion test (43).
introduction
Materials and methods Results
and Discussion back
to top
Results
The main advantages of a bulk milk
diagnostic test are that the sample is easy to obtain and the test is reasonably
cheap, and can therefore be used as a routine indicator of subclinical diseases.
This also yields data for use in epidemiological studies and for studying the
genetic background of diseases. Pertinent parts of the milk profile outlined
above have been used to study the heritability of ketosis and mastitis (3). Bulk
milk tests provide a good starting point for differential diagnosis, in
additition to their value for blood serological monitoring. It is envisaged that
veterinary practices could record the information from bulk milk tests and
incorporate it into preventive medicine programmes, particularly in relation to
purchased animals (41). Regular testing of bulk milk samples
every few months provides a simple low cost method of confirming
continuing freedom from infection in known disease-free herds; including those
at potential risk of introducing new infection, and thereby allows opportunity
for prompt action if indicated. For example, a positive result in a previously
negative herd could herald an upsurge in infertility, abortions or milk drop
(1).
During a one year observation study we
established a 35.2 % incidence of hypocalcemia with 4.5 % incidence of milk
fever, 12.56 % incidence of hypophosphatemia, 23.5 % incidence of
hyperketolaktia, 21.38 % incidence of clinical mastitis and 56.24 % incidence of
increased SCC (>400.000/ml) in individual milk samples. By bacteriological
analysis of milk samples from clinically (n=57) and subclinically (n=81)
infected cows (>400.000/ml) 57% S. aureus, 32% other streptococci, 6% E. coli,
4% S. agalactiae, 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, somatic 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 count
493,000±122,124 sc/ml was too high. Namely, 44% of samples contained over
400,000 sc/ml. The results also demonstrated that 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. It was 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 protein content decreases if somatic cell count increases. All these
parameters were statistically significant with the exception of protein 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
(13.46%) positive responses were established. A detailed analysis has revealed
that acetone was mainly due to feeding grass silage with an elevated butyric
acid content, the so-called alimentary or false ketosis (5). Using the analysis
of variance with 5 entries we calculated F-values and established statistical
significance of individual factors affecting milk parameters. In Table 4
F-values for 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, quite objective because there are great differences among herds with
regard to the management regime and health condition of dairy cows. Similar
reports have been obtained by others (3,20,45). Season (temperature, humidity,
husbandry) had also a significant effect on the majority of parameters,
especially on fat, proteins and urea levels as well as somatic cell count.
Through July, August and September the cell count was highest and the mastitis
was most frequently observed (44). The authors reported that the cell count was
also affected, in addition to mastitis, by a whole range of factors, including
the time of the year, and ensuing changes in feeding and husbandry (44,46).
The results confirm that the
concentration of Na, Cl and LDH activity are closely related to somatic cell
count. An increased cell count results in Na, Cl and LDH increases. This finding
indicates that the results of the MLP-test should be interpreted from various
viewpoints. The most frequently established clinical state in cows is depressed
milk secretion due to mastitis. In such cases elevated cell counts (>350,000
sc/ml), elevated Na content (>23.00 mmol/L), Cl (>34.00 mmol/l and LDH
activity (>80.00 U/L) were observed. Metabolic disorders in bulk milk samples
associated with acetone content (ketolactia) were less frequently detected. The
concentration of protein and Na was markedly lower in bulk milk. Acetone appears
in various forms of ketosis with impaired metabolism of carbohydrates and lipids
which is reflected at least at the initial stage in the compensated rumen with
metabolic acidosis. The established acetone bulk milk Na content below 22.5 mmol/L
as well as suppressed milk secretion are sensitive indicators of metabolic
disorders. Milk protein content is also decreased, whereas the somatic cell
count is below 250,000 sc/ml. Similar findings have been reported by others who
suggested the same milk parameters monitored for 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 for the protein percentage and as much as 53.7% of variance was
explained. Determination coefficients were rather high also by milk
concentrations (above 22.5%) with the exception of K (5.5%). Thus, the model
encompasses the majority of factors significantly affecting milk composition.
Up to 1987 there were no positive EBL reactors to our knowledge in Slovenia (49). All bulk milk and individual blood samples were negative for EBL.
Table 3: Association of mean weekly ( n = 416)
values of bulk milk parameters with housing and feeding, season, udder health
status, ketolactia and lowest and highest mean concentrations in 8 herds
|
Effects |
n |
Fat |
Prot. |
SCC |
Na |
K |
Cl |
LDH |
Urea |
|
|
|
% |
% |
x 10003 |
mmol/L |
mmol/L |
mmol/L |
U/L |
mmol/L_ |
|
Tied |
312 |
4.15 |
3.34 |
421 |
21.18 |
38.14 |
35.36 |
73.62 |
4.21 |
|
Loose |
104 |
4.32 |
3.43 |
702 |
22.78 |
38.07 |
37.42 |
92.71 |
4.76 |
|
Winter |
232 |
4.21 |
3.41 |
441 |
21.46 |
38.11 |
35.89 |
77.96 |
3.98_ |
|
Summer |
184 |
4.31 |
3.32 |
512 |
21.79 |
38.15 |
37.98 |
80.10 |
5.52 |
|
SCC 1* |
11 |
4.09 |
3.42 |
77 |
20.94 |
38.09 |
33.78 |
50.23 |
3.93_ |
|
SCC 2* |
14 |
4.18 |
3.39 |
178 |
21.06 |
38.11 |
34.09 |
57.81 |
4.28 |
|
SCC 3* |
96 |
4.20 |
3.36 |
319 |
21.69 |
38.14 |
34.18 |
58.34 |
4.39 |
|
SCC 4* |
267 |
4.19 |
3.29 |
532 |
23.52 |
38.12 |
36.87 |
82.13 |
5.39 |
|
SCC 5* |
28 |
4.21 |
3.25 |
1021 |
24.19 |
38.10 |
39.16 |
110.31 |
5.56 |
|
Acetone (-) |
360 |
4.18 |
3.41 |
432 |
23.46 |
38.12 |
35.91 |
77.99 |
4.57 |
|
Acetone (+) |
56 |
4.21 |
3.29 |
529 |
21.58 |
38.14 |
36.14 |
81.23 |
4.06 |
|
Min. ** |
|
3.59 |
3.84 |
351 |
20.00 |
37.25 |
34.34 |
65.02 |
2.16 |
|
Max |
|
4.46 |
4.49 |
963 |
24.60 |
39.45 |
38.44 |
114.26 |
6.32 |
|
Total |
416 |
4.19 |
3.37 |
493 |
21.59 |
38.12 |
35.86 |
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 (R2) and coefficient of variation (CV)
|
Variability
sources |
Fat
% |
Prot.
% |
Urea
mmol/L |
||||
|
Farm |
*** |
*** |
NS |
*** |
|||
|
Housing
system |
* |
NS |
NS |
NS |
*** |
||
|
Season |
* |
NS |
NS |
NS |
|||
|
SCC
- class |
NS |
* |
NS |
||||
|
NS |
NS |
* |
NS |
NS |
|||
|
36.0 |
53.7 |
32.2 |
27.4 |
22.5 |
5.5 |
23.2 |
|
|
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 many veterinary surgeons and farmers are unaware of the health
status of their herds. Bulk milk tests offer an ideal opportunity to improve
this situation and stimulate an interest in monitoring herd health status,
adopting appropriate control measures including vaccination and screening new
stock. In future bulk milk antibody tests for Salmonella typhimurium and
Neospora caninum will be introduced. Knowledge of herd health status is
particularly relevant at present because many previously closed herds are now
purchasing replacements following of the cull for bovine spongiform
encephalopathy. In some countries, bulk milk antibody test have provided a
simple and convenient means of surveying the infectious disease status of their
herds. On the basis of this and recent research
we recommend for evaluation of the herd health status (metabolic, udder
diseases) with bulk milk analysis with the 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 >38.00 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 (Project L4 - 5473 - 04505 - 97).
introduction
Materials and methods Results
and Discussion back to top
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