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Abstract
This study was carried out at the Experimental Farm and the Animal Physiology Research Lab, Faculty of Agriculture, Cairo University, Giza, Egypt, during the summer season of 2004. The objective of the present work was to assess the relevant physiological responses and growth performance of buffalo calves to artificial constant severe heat stress (40 °C), comfort (25 °C) and outdoors natural climatic conditions. Eight buffalo calves were used, their age and live body weight were 6 months and 118.00 to 119.25 kg, respectively. All the calves responses were assessed under two constant thermal conditions, heat stress (40 °C and 87.5% RH, lab A) and comfort state (25 °C and 64.5% RH, lab B). two trials, each of one month, in both labs were interrupted by 15 days period under natural climatic outdoors conditions. The responses to these fixed conditions were discussed and compared to the responses under outdoors natural climatic conditions (June) during a preliminary period and during the interrupting in August.
Both groups showed increase in RT and RR at 14:00 over that at 08:00h during the both trials in the two labs. The RR during the 1st trial was slightly higher compared with that of the 2nd trial. The RR increased dramatically in the heat stressed calves to reach 6-7 times that of those under comfort conditions. Water intake was increased due to heat stress. Feed intake (FI) either concentrate (CFI) or roughage (RFI) intakes were greater for group B compared with group A during the two trials. Values of Ht, Hb and RBCs were reduced by heat stress during the two trials. The WBCs was significantly increased (around 50%). Levels of TP, Alb, TL, TG, TC, Glu and BUN decreased by heat stress during the two trials, while, the Glb level was not affected. In the two trials, heat stress caused slight increase (4 to 8 %) in Na and K, increase (47 to 58 %) in P level and Ca decreased by 20%. In both trials, heat stress decreased Ins, increased Glg and , both T3 and T4 droped by about 50%. The first exposure of the calves to HSC caused drop (13%) in their BW from 119 to 104. the second exposure did not cause any further drop in BW. In comparison, the calves under CTC showed 28% and 9% increase in their BW during the first and second exposure, respectively. The two calves groups showed almost equal percentages of increase in BW (1.4 and 1.5%) during the outdoors interrupting. Heat stress caused reduction in the weight of the visceral organs. Fasted BW and empty BW were decreased. Heat stress caused decrease in the length of small and large intestine and appendix. Fat percentage in the lean meat reduced due to heat stress in both longissmus dorsi and semitendinosus muscles.
Concluded the buffalo calves were successful in sustaining their lives, however, by drastic changes in their physico-chemical internal body status which lead to delay or even arrest of growth and proper thermal environment will enhance growth efficiency.