REPRODUCTIVE CYCLE STAGE BIAS IN PHYSIOLOGICAL AND IMMUNE RESPONSES TO ENDOTOXIN CHALLENGE IN MURRAH BUFFALOES (Bubalus bubalis)

Reproductive cycle in large domestic animals has a distinctly different hormonal milieu with estrus dominated by estrogen and diestrous by progesterone. Since the sex steroids are caught up in disease severity, present study investigated variability in immune responses upon endotoxin challenge at day 0 (estrous) and day 10 (diestrous) of the reproductive cycle in Murrah buffaloes. Physiological responses like rectal temperature, heart rate, pulse rate and immune responses like plasma TNF alpha, nitric oxide, xanthine oxidase, cortisol and glucose were evaluated before and after LPS challenge (E. coli 055:B5 0.6 mu g/kg body weight). Physiological as well as immune responses were heightened during estrous as compared to the diestrous stage of the cycle after endotoxin challenge. The area under the curve (AUC) for rectal temperature and heart rate was significantly (P<0.05) higher at estrous as compared to diestrous. Integrated responses of TNFa, nitric oxide and xanthine oxidaes to LPS challenge calculated as AUC were significantly (P<0.05) higher at estrous as compared to the diestrous stage of the estrous cycle. AUC for plasma cortisol, an anti-inflammatory mediator, was significantly (P<0.001) higher at the diestrous than the estrous stages of cycle. During first 2 h of endotoxin insult, hyperglycemia was registered which culminated in hypoglycaemia. Total leukocytes were higher in the estrous than the diestrous stage but endotoxin challenge did not affect the total counts. However, there was neutrophilia after endotoxin challenge in both the stages of the reproductive cycle in buffaloes. The results indicate that the underlying physiological attributes of stage of reproductive cycle represents a source of variability in immune competence when challenged.