The effects of long-term thrice-daily milking on milk secretion in the goat: evidence for mammary growth

Abstract

Goats were milked twice daily for 2-4 weeks after parturition. For the remaining 9 months of lactation, the right mammary gland was milked thrice daily while the left gland was milked twice daily. In the first and second weeks of thrice-daily milking the milk yield of the right gland increased relative to the left gland. Subsequently there was only a slight increase in the difference in milk yields between the glands, which reached a maximum after 10 weeks. Total yield of the right gland for the period of thrice-daily milking was significantly higher, by 30%, than that of the left gland. The peak yield of the right gland was significantly greater, by 29%, than that of the left gland. There was no significant difference between the rates of decline of yield (persistency) from peak lactation. There were no significant differences in the composition of the milk from the two glands with respect to Na+, K+, Cl-, lactose, protein, citrate, fat or calcium. At 40 weeks of lactation the weight of the right gland was significantly higher than that of the left gland and the weight of the parenchyma of the right gland was also significantly higher, by a similar percentage. At this stage of lactation, milk yield of the right gland was 43% higher than the left gland, while the weight of tissue was 34% higher. Thus over three-quarters of the difference in yield was accounted for by the greater gland size, and the remainder by greater milk secretion per unit weight of tissue.(ABSTRACT TRUNCATED AT 250 WORDS)