It is common knowledge that colostrum or ‘first’ milk produced by dams in the first few days postpartum is critical to the health and vitality of newborn calves. Providing sufficient amounts of high-quality colostrum is one of the primary factors in preventing newborn calf diseases and reducing economic losses. Understanding the various components of colostrum and its important functions can help producers utilize best management strategies to maximize benefits from this essential nutrient.
Colostrum contains over ninety compounds that fight against pathogens and establish immune response (immunoglobulins, lactoferrin, lactoperoxidase); provide nutrients (lactose, lipids, protein); and stimulate growth and generation of nerves, cartilage, bone, and muscle (essential fatty acids, minerals). Compared to mature bovine milk, colostrum contains higher total solids (27.6% vs. 12.3%), higher protein (14.9% vs. 2.8%), and slightly higher fat (6.7% vs. 4.4%) (Christiansen, 2010). The quality and quantity of colostrum produced is affected by breed type, cow age, and nutritional status of the dam. Dairy cows typically produce more colostrum than beef cows, and mature cows produce more than heifers. Feeding energy-deficient diets can significantly reduce colostrum yield. In addition, factors such as temperature stress, dystocia or calving difficulty, and lack of mothering (licking the calf dry after birth) can reduce the ability of the newborn to absorb immunoglobulins in colostrum.
One of the most important functions of colostrum is to deliver immunoglobulins that transfer passive immunity to the calf and enable it to fight off infections for the first three-to-five weeks of life. This is accomplished by absorption of antibodies through the wall of the newborn’s small intestine. For maximum transfer of antibodies, the newborn must receive colostrum soon after birth. Antibody transfer becomes more limiting over the first 24 hours after birth as permeability of the newborn gut is reduced and the concentration of immunoglobulins in colostrum decreases (Figure 1).
Figure 1. Effect of age of calf on the percent absorption of immunoglobulin through the calf intestine.*
*Adopted from Arthington et al., 2008.
The principal colostral immunoglobulin is “IgG,” which is commonly measured in the serum of the calf after birth to determine successful transfer of passive immunity. If transfer does not occur, calves are considered to have “FTP”, or “Failure of Passive Transfer,” which is highly correlated to illnesses such as diarrhea and other more serious diseases, such as colisepticemia, caused by absorption of certain serotypes of E. coli. Generally, calves with serum IgG concentrations of less than 10 g/L are thought to be at higher risk of disease. Calves with severely low concentrations of immunoglobulins typically die within days.