The present study was conducted to determine the effect of increasing temperature humidity index (THI) on lactating Murrah buffalo. The study was conducted on six lactating buffaloes which were offered the same basal diet and were blocked by days in milk, milk yield and parity. The study was conducted during May, June and July with average THI of 79.88, 80.57 and 85.36, respectively. Milk yield was recorded twice a day at 06:00 and 18:00 h and physiological parameters were recorded and blood was sampled on 30th day of each month at 14:30 h. The results showed a significant decrease (P LT 0.05) in milk yield in buffaloes only at a THI of 85.36 as compared to THI up to 80.57. The rectal temperature (RT) did not change (P=0.580) with increasing THI up to 85.36, however, the respiration rate (RR) and pulse rate (PR) changed (P LT 0.05) progressively with increasing THI. Leucocytopnoea, lymphocytopnoea and neutrophilia; and alteration in serum urea, alkaline phosphatase activity, reactive oxygen species and phosphorus concentration were observed only at a THI of 85.36 as compared to THI up to 80.57. Similarly, significant (P LT 0.05) alteration in serum T4, cortisol and prolactin levels were observed at a THI of 85.36 as compared to THI up to 80.57. It can be concluded that lactating buffaloes experienced mild heat stress up to a THI of 80.57 (May and June) and a moderate type of heat stress at a THI 85.36 (July).

To evaluate the role of dietary supplementation of astaxanthin, prill fat and their combination on antioxidants and immune status of lactating buffaloes during heat stress. Twenty four lactating buffaloes (first to fourth parity) were selected and divided equally into four groups i.e. Group I (control), Group II (astaxanthin 0.25 mg/kg body wt/day), Group III (prill fat 100 g/animal/day) and Group IV (astaxanthin + prill fat). Plasma was separated from the blood collected at fortnightly interval for the analysis of antioxidant enzymes and interleukins levels. The levels of superoxide dismutase and catalase were significantly lower in astaxanthin supplemented groups (Group II and Group IV) compared to Group I and Group III. The levels of pro-inflammatory cytokine (Interleukin-2) was significantly (P LT 0.05) lower in astaxanthin supplemented groups (Group II and Group IV) compared to Group I whereas levels of anti-inflammatory cytokines (Interleukin-10) was significantly (P LT 0.05) higher in all supplemented groups (Group II, Group III and Group IV) than Group I. Results showed that, dietary supplementation of astaxanthin (potent antioxidant) was able to alleviate the heat stress induced changes by lowering the levels of antioxidant enzymes (SOD and CAT) and pro-inflammatory cytokine (IL-2) and improving the levels of anti-inflammatory (IL-10) cytokines in lactating buffaloes during summer season.