Effects of high environmental temperature on physiological status, energy and nitrogen metabolism of Holstein heifers in late stage of growth

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  • ホルスタイン種育成後期牛の生理および窒素・エネルギー代謝に及ぼす高温の影響
  • ホルスタインシュ イクセイ コウキギュウ ノ セイリ オヨビ チッソ ・ エネルギー タイシャ ニ オヨボス コウオン ノ エイキョウ

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Abstract

A series of studies were carried out to investigate the effects of increasing environmental temperature (20°C, 28°C and 33°C) under a constant (60%) relative humidity (RH) on physiological responses, utilization of nutrients and nitrogen and energy metabolism of Holstein heifers in late stage of growth (n = 4, initial body weight = 418 ± 14 (± SE) kg, initial age = 17.1 ± 0.5 months). All the heifers were fed Italian ryegrass silage and concentrate to meet their energy growth rate of 0.8kg/day. The energy balance was measured daily by means of indirect calorimetry on the last 4 days of each 14-day treatment period. The results were as follows ; 1) Respiration rate and rectal temperature rose with increasing environmental temperature, while dry matter intake of roughage dropped. 2) Digestibility of dry matter, crude protein and nonfiber carbohydrate in the feed were higher at 33°C than at 20°C. 3) Total mean retention time of feed in the digestive tract at 33°C was significantly longer than at 20°C and 28°C. 4) Blood alanine aminotransferase, total cholesterol, triiodo-thyronine and alkaline phosphatase at 33°C were lower than at 20°C ; however, triglyceride was higher. 5) Nitrogen balance was significantly affected at 28°C and above. Fecal nitrogen at 33°C, expressed as a percentage of intake, was lower than that at 20°C and 28°C ; conversely, urinary nitrogen at 33°C, expressed as a percentage of intake, was higher than that 28°C. 6) Energy balance was significantly affected at 28°C and above. Heat production, expressed as metabolic body size, decreased as environmental temperature in-creased, however, heat production, expressed as gross energy intake, increased. Retained energy at 33°C was lower than at 20°C and 28°C, however, energy distribution to body fat or body protein did not change as environmental temperature increased. These results show that the detrimental effects of high environmental temperature on the performance of Holstein heifers in the late stage of growth appeared at 28°C and above ; and that the influence of high environmental temperature on heifers was severer in the late stages of growth than in the early stage.

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