Milk Production and Biosynthesis

Milk is the source of nutrients and immunological protection for the young cow. The gestation period for the female cow is 9 months. Shortly before calving, milk is secreted into the udder in preparation for the new born. At parturition, fluid from the mammary gland known as colostrum is secreted. This yellowish coloured, salty liquid has a very high serum protein content and provides antibodies to help protect the newborn until its own immune system is established. Within 72 hours, the composition of colostrum returns to that of fresh milk, allowing to be used in the food supply.

The period of lactation, or milk production, then continues for an average of 305 days, producing as much as 9000-10,000 or more kg of milk. This is quite a large amount considering the calf only needs about 1000 kg for growth.

Within the lactation, the highest yield is 2-3 months post- parturition, yielding 40-50 L/day. Within the milking lifetime, a cow reaches a peak in production about her third lactation, but can be kept in production for 5-6 lactations if her health and milk yield are still good.

Graph representing Milk Yield (kg/day) and Weeks of Lactation. Milk Yield declines at -9% per month after peak lactation

About 1-2 months after calving, the cow begins to come into heat again. She is usually inseminated about 3 months after calving so as to come into a yearly calving cycle. Heifers are normally first inseminated at 15 months so she's 2 when the first calf is born. About 60 days before the next calving, the cow is dried off. There is no milking during this stage for two reasons:

- milk has tapered off because of maternal needs of the fetus
- udder needs time to prepare for the next milking cycle

The life of a female cow can be summerized as follows: 

 Age 

0                          Calf born
15 mos                Heifer inseminated for first calf
24 mos                First calf born - starts milking
27 mos                Inseminated for second calf
34 mos                Dried off
36 mos                Second calf born - starts milking
Cycle repeats for 5-6 lactations.