الفهرس 
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Abstract
Due to the importance of water metabolism in thermoregulation especially under heat stress, this investigation was carried out to study the effect of high ambient temperature, separated from of her climatic factors which were maintained constant, on live body weight, water metabolism components, total body water, total body solids, water turnover rate, biological half life-time of tritiated water and rectal temperature and cardiorespiratory rate. Twelve dry Friesian cows of 3-years old were placed in metabolic cages inside climatic chambers. Animals were subjected to two successive treatments. First, mild treatment, where the environmental temperature and relative
humidity were kept constant at 160 C and 62%, respectively for 7-hours a day. The second treatment (heat s tress treatment), where the environmental temperature and relative humidity were 39°C and 62% R.H., respectively
for 7 hours a day. Each experimental treatment lasted 11 days. The data were collected during the last 8 days .
New tracer methods using TOH dilution technique were developed in this study for determining each of total water intake t total evaporative water loss, heat tolerance coefficient and water retention.