ALTERATION IN IMMUNE RESPONSIVENESS DURING THE PERIPARTUM PERIOD AND ITS RAMIFICATION ON DAIRY-COW AND CALF HEALTH

Substantial evidence indicates that innate and acquired defense mechan isms are lowest from 3 wk precalving to 3 wk postcalving. This lowered responsiveness includes aspects of systemic and mammary gland immunit y that may account, at least in part, for the increased incidence of p eripartum disease. The physical and metabolic stresses of pregnancy, c alving, and lactation may contribute to this decrease in host resistan ce and the subsequent increase in disease incidence. However, variatio n among cows in their host resistance mechanisms suggests that genotyp e and phenotype may possibly be used to identify cows that are able to mount beneficial immune responses over the periparturient period. Our own studies suggest that cows may be categorized as high or low respo nders based on the peripartum antibody responses to ovalbumin and Esch erichia coli J5. Low responders were hyporesponsive to these test anti gens and had a higher incidence of peripartum diseases, particularly m astitis. In many species, a functional link exists between the immune and endocrine systems, and, during periods of stress or physical injur y, neuropeptides and neuroendocrine hormones function as immunomodulat ors. Initial investigations of peripartum cows reveal positive relatio nships between growth hormone kinetics and profiles of antibody respon se. Whether hormone fluctuations during the periparturient period are responsible for the alterations observed in immune responsiveness rema ins uncertain.