Nutrition and Immunity for Pre-weaned Dairy Calves

Dairy calves are extremely susceptible to gastro-intestinal disease during the pre-weaned period. The risk for enteric disease decreases as the calf ages; therefore, it is important to break the pre-weaned period up into at least 2 distinct phases that likely need to be managed differently, early life (1st and maybe the 2nd week of life) and the remaining time the calf is fed fluid. When a calf is born, they have never been exposed to any microorganisms and some aspects of their immune system are not fully developed. Since the calf in utero received its nutrients from the cow through placental transfer, the calf has never had any enteric nutrition. After birth, the calf is now in a microbial world and expected to receive all its nutrients orally from its mother's milk. The gastro-intestinal tract of the calf is naive and develops rapidly during the first few days to weeks. The cells that make up the gastro-intestinal tract are the first line of defense of the immune system; therefore, until the cells are more adult-like, the calf is at an increased risk for developing gastro -intestinal diseases. Future research needs to focus on how much, the frequency of feeding, and composition of fluid fed affect the calf during this period. Currently, the primary strategies to improve the resistance to gastro-intestinal diseases during this period are focused on decreasing the interaction of potential pathogens with the cells of the calf's gastro-intestinal tract. The uses of prebiotics, probiotics, hyper-immunized egg protein, and spray-dried plasma proteins have all been shown to decrease the incidence of gastro- intestinal diseases and improve the growth of pre-weaned calves. The plane of nutrition that calves are fed during the entire pre-weaned period was reported to improve future lactational performance and emerging data suggest that it may improve the resistance to some diseases. Further, the effect may persist past the pre-weaned period. More research is needed in this area. Nutrition can influence disease resistance of calves in many ways, both directly by supplying specific nutrients and indirectly by influencing the exposure to microorganisms.