The calf has essentially no immune protection at birth because maternal immunoglobulins cannot cross the placenta, and the calf�s own immune system is functionally immature. The calves are lymphopenic at birth. Leukocytes from calves produced unusually high concentrations of NO when compared with those produced by cows, thus constituting a possible indicator of the immaturity of the immune system of the neonatal calf. The calf’s acquisition of colostral immunoglobulins through absorption in the intestine is called passive transfer or passive immunity. In addition to disease protection, colostrum also provides the neonatal calf with high quality nutrition and many growth factors and hormones that may be beneficial for initiating function and growth of the digestive tract. “Failure of passive transfer” (FPT) occurs when the acceptable levels of IgG or total protein are not achieved by 24-48 hr after birth. Timely, adequate colostrum intake is the single most important management factor affecting morbidity and mortality in preweaned calves. The two most important factors affecting the amount of IgG absorbed from colostrum are the time of first feeding and the amount of IgG consumed. IgG more than 10g/L is optimal for neonatal survival. 1302763578.php