EFFECTS OF A DECREASE IN MILK-YIELD, CAUSED BY ONCE-DAILY MILKING OR BY RESTRICTED FEEDING, ON THE SOMATIC-CELL COUNT IN MILK FROM COWS WITH OR WITHOUT SUBCLINICAL MASTITIS
Cw. Holmes et al., EFFECTS OF A DECREASE IN MILK-YIELD, CAUSED BY ONCE-DAILY MILKING OR BY RESTRICTED FEEDING, ON THE SOMATIC-CELL COUNT IN MILK FROM COWS WITH OR WITHOUT SUBCLINICAL MASTITIS, Australian Journal of Dairy Technology, 51(1), 1996, pp. 8-11
1. Two experiments were carried out with grazing Holstein Friesian cow
s which had either low somatic cell counts (SCC) or high SCC before th
e treatment period began. They were designed to measure the effects of
two factors, other than bacterial infection, on SCC. In experiment 1,
32 cows in mid lactation were subjected to a 3 week experimental peri
od of either generous or severely restricted feeding. In experiment 2,
36 cows in late lactation were subjected to a 4 week experimental per
iod of either twice daily or once daily milking. 2. The yield, composi
tion and SCC in milk from each cow were measured twice weekly, and the
bacteriological status of each quarter was examined on two days befor
e and after the experimental period. 3. In both experiments the cows w
ith high initial SCC had a higher proportion of quarters which were in
fected, some with major pathogens, while none of the cows with low ini
tial SCC had quarters which shed major pathogens. 4. In experiment 1,
the large decrease in milk yield (-30%) caused by the restricted level
of feeding had no consistent effect on the yield of somatic cells or
the SCC. However, the decrease in milk yield was associated with decre
ases in the yield of somatic cells and the SCC in the cows with low in
itial SCC but relative increases in the cows with high initial SCC; an
d the interactions were significant (P < 0.05; 0.12). 5. In experiment
2, once daily milking caused a larger decrease in daily milk yield in
cows with the high initial SCC than in those with the low initial SCC
(interaction P < 0.01). Once daily milking did not affect yield of so
matic cells, but it did cause increases in SCC, with the effect being
larger in the cows with high initial SCC (interaction P = 0.10). 6. Th
e results of both experiments showed that SCC can be used to distingui
sh between uninfected and infected cows in mid and late lactation desp
ite wide variations in feeding and milking. In fact the difference in
SCC between infected and uninfected cows may be increased by the effec
ts of reduced feeding or once daily milking. 7. In practical terms, th
e results of Experiment 1 indicate that maintenance of a high daily yi
eld may help to reduce the adverse effects of subclinical mastitis, an
d the results of Experiment 2 indicate that cows with low SCC are more
resilient to the adverse effects of once daily milking in late lactat
ion.