The Thai Journal of Veterinary Medicine


The present study was undertaken to determine the diurnal pattern of hormone levels in buffaloes, and the effects of heat stress on plasma hormone concentrations. Eight buffalo heifers aged 2-3 years were selected for the experiments. They were divided into shade and nonshade groups for 20 days. for 20 days. The blood samples were collected from indwelling catheterized jugular vein and sera were se- parated. The physiological changes for heart rate, respiratory rate and body temperature were recorded. Serum Cortisol, Triiodothyronine {T}, Prolactin (PRL) and Growth Hormone (GH) concentrations were determined by using RIA procedures at the Environmental Physiology Laboratory, UMC, USA. Serum Cortisol levels significantly increased from 3.9 ± 0.54 ng/ml. for shade AM {25°C) to b.4 ± 0.59 ng/ml. for nonshade PM {35°C} {P < .05}. Serum PRL increased linearly from 36.8±3.92 ng/ml. in shade to 117.3±8.83 ng/ml. of nonshade period. Indications of correlation between thermal humidity index {THI} and serum concentrations of PRL and cortisol were obtained. The average T, level (0.38±0.02 ng/ml in the morning shade groups was not significantly different when compared with that in the afternoon nonshade group (0.34±0.021 ng/ml). The GH levels nonsignificantly decreassed from 4.4±0.14 ng/ml. of shade period to 4.2± 0.14 ng/ml. of nonshade period.

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