Lactation curve
The cow reaches her peak milk production approximately 3 to 6 weeks after parturition, and then a gradual decline in the yield takes place. A lactation period of 305 days is recommended to take advantage of 60 days of dry period and yearly calving interval. The body condition at calving of the cow is determines peak milk yield. Good body condition at calving and adequate feeding program after calving tend to increase peak milk production. There is a high correlation between global lactation and peak milk production.
The rate of decline in yield after calving is called persistency. Cows that have a sharp decline in milk yield after the peak have a low persistency. Cows must have high persistency as well as high production for high-lactation milk yields. The rate of decline is accentuated by pregnancy, particularly starting at the twenty-second week of pregnancy, which occurs during the seventh to eighth months of the normal lactation period if the cow is bred back 60 days after calving.
There is a general inverse relationship between milk yield and milk protein and milk fat contents. As yield increase, the percentage composition of these two elements decrease. The protein and milk-fat percentages are at a low point during the peak of lactation and then gradually increase toward the end of lactation. Lactose content shows a very slight decline toward the end of lactation and ash content shows a very slight increase with advancing lactation.
