Second and later lactation cows will produce more than twice the colostrum and have a greater variety of Igs because they will have been exposed to a wider range of diseases than heifers. Colostrum of older cows will provide greater protection against diseases than that of first calf heifers. Cows should also have had at least a 40 day dry period to ensure adequate levels of Ig in colostrum. The composition and characteristics of colostrum and whole normal milk is shown in the following table. Total solids, protein, and ash contents are higher in colostrum than normal milk with the decrease in solid content occurring within the first week after calving.
Colostrum contains lower levels of lactose than normal milk.
This may be a protective mechanisms to reduce the incidence of scours in newborn calves. The 10 fold higher content of vitamin A in colostrum may serve to protect mucosal linings in the digestive tract against infection and also to increase vitamin A levels within the calf. Newborn calves should be fed colostrum immediately after birth to maximize protection against infection. The highest absorption of Igs occurs during the first 6 hours after birth which decreases to zero after 24 to 48 hours. The percentage of calves showing absorption of intact Igs with time after birth is shown in the following table.