Two groups of 12 cows were fed and managed identically throughout the whole lactation, except that one group was milked twice daily, whereas the other group was milked only once daily. The cows were aged 3 years and older, and included 6 pairs of identical twins. Yields of milk, fat and protein were: 4320 and 2810 kg milk ; 208 and 144 kg fat; 162 and 110 kg protein for the twice and once daily groups respectively and the differences were significant. However in three pairs of twin cows, once daily cows produced more than 90% of the yield produced by their twice daily twin mates. Lactose concentrations were significantly higher for the twice daily group, 5.05 and 4.82% lactose. Somatic cell counts were significantly lower for the twice daily group throughout lactation, even though there appeared to be no difference in the incidence of infection measured at the end of lactation. The twice daily group lost weight and body condition during lactation, even though they appeared to eat slightly more feed than the once daily group which gained weight and body condition. The twice daily group had lower plasma concentrations of glucose during early lactation than the once daily group, but there were no differences in concentrations of calcium, magnesium or Beta hydroxybutyrate between the groups. The results show that although once daily milking does cause significant decreases in yields of milk and its components, some cows were only slightly affected. Selection of tolerant cows, plus appropriate management such as longer lactations and high stocking rates, may offer a useful method of increasing labour productivity and reducing costs of production.
Proceedings of the New Zealand Society of Animal Production, Volume 51, , 443-446, 1991
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