Immunity Development in Newborn Calves: a Review

The fetus is primarily protected by the innate immune system, however fetal phagocytic activity does not become completely developed until late in gestation. Due to the lack of transplacental antibody exchange from maternal to fetal circulation in the bovine during gestation, newborn calves are born with very low levels of the immune system's primary antibody, known as agammaglobulinemia. It has been recommended that at least 4 liters of colostrum with an Ig concentration of at least 50 g/L is necessary to ensure effective passive immunological transmission in dairy calves. Bovine colostrum contains a diverse range of critical immunological and nutritional components, including immunoglobulins, which are actively transferred from the maternal serum to the mammary gland. Colostrum contains a high concentration of leukocytes (1-3 million cells/mL), the most abundant type of immune cell. Immunoglobulin transfer from colostrum has long been recognized as essential to the health of a calf. A decrease in preweaning mortality and morbidity, an increase in growth, and an increase in future milk production can all be achieved by increasing IgG uptake. However, there are various factors affecting passive immune transfer; maternal heat stress during late pregnancy has an impact on calf function in the postnatal period. Additionally, late gestation heat stress impairs the cellular immunity of preweaning calves as well. Therefore, to prevent adverse effects on the calf, it is essential to adequately manage the colostrum quality, the quantity of colostrum, and the heat stress experienced by dry cows.