Impact of Heat Stress on Growth Performance and some Blood and Physiological Parameters of Suckling Friesian Calves in Egypt

Forty newly born male and female Friesian calves including 20 calves during the winter season and 20 calves summer season 2020, were used to study the effect of heat stress on live body weight, body weight gain, feed intake, feed and economic efficiency during suckling period. Ambient temperature, relative humidity and temperature humidity index were markedly higher during summer in compression with winter season. Digestibility coefficients of all nutrients (DM, OM, CP, CF, EE and NFE) and feeding values (TDN and DCP) reduced significantly (P<0.05) for summer ration compared to winter ration. Ruminal pH value and ammonia nitrogen concentration were higher significantly (P<0.05), however total VFA concentration was lower significantly (P<0.05) for summer than winter season. Concentrations of serum total protein, globulin and glucose were higher significantly (P<0.05), however, albumin to globulin ratio, concentrations of urea and creatinine and activity of AST and ALT activity were lower significantly (P<0.05) for winter season compared to summer season. Hemoglobin (HGB) concentration and counts of white blood cells (WBC) and red blood cells (RBC) were declined significantly (P<0.05), however, haematocrit percentage (HCT), mean cellular volume (MCV), mean cellular hemoglobin (MCH) and mean cellular hemoglobin concentration (MCHC), were raised significantly (P<0.05) for summer season than those of winter season. Intake of TDN, CP and DCP were higher significantly (P<0.05) for winter season than those of summer season. Weaning weight, total weight gain and average daily gain were higher significantly (P<0.05) for winter season in comparison with summer season. The amounts of DM, TDN, CP and DCP per kg weight gain were lower significantly (P<0.05) for summer season compared to winter season. Feed cost per kg weight gain was higher significantly (P<0.05), however, output of ADG, net revenue and economic efficiency were higher significantly (P<0.05) for winter season than those of summer season. All physiological parameters such as rectum temperature (RT), skin temperature (ST), respiration rate (RR) and pulse rate (PR) were higher significantly (P < 0.05) during the summer compared to the winter season.