The average gross composition of cow’s milk is as follows:
- Water – 87%
- Fat – 3.7%
- Lactose – 4.9%
- Proteins – 3.5%
- Ash – 0.7%
However, the composition of milk from individual cows may vary considerably from these average values. Breed differences, the time of year, the time of day, individual differences, the age of the cow, the period of lactation, the portion of any one milking, feeding, etc., are some factors that may contribute to variation in the composition of milk.
Variation in milk composition due to breed are of the greatest magnitude. Jersey, Guernsey and Ayrshire cows gives milk richer in fat than Holstein cows. Usually milk obtained in the fall and early winter is richer than obtained in the spring and the summer. The morning milk usually is richer in fat than evening milk, at times by almost 2%.
The first portion (or fore milk) of milk drawn in the milking process are lower in fat than the last portions (or strippings). Milk obtained the first few days after calving is known as colostrum and differs materially from normal milk. During the final stages of lactation, when the daily production of milk is decreasing, there is some increase in percentages of fat and casein. The differences in milk composition occur mainly in the relative amounts of fat, protein, and water. The percentages of ash and lactose remain fairly constant in normal milk regardless of the amount of other components.
Composition of Milk
