الفهرس 
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Abstract
Due to the importance or mineral metabolism in thermoregulation
especially under heat stress, this investigation was carried out to study the effect of high environmental
temperature, separated from other climatic factors which were maintained constant, on Ca, P, Mg, Na, K, Fe, Cu, Zn and Cobalt metabolism, using the total mineral intake, total urinary. And fecal mineral excretion measurements, also, the retention for each mineral were calculated. The second objective of this study was to compare between Neutron activation and conventional techniques for Ca, Na, h., Fe, Zn and cobalt determination. Eight dry Fries heifers were placed in metabolic cages inside climatic chambers. Animals were subjected to tow
succeaive treatments. First, mild treatment, were the environmental temperature and relative humidity were kept constant at 16°C and 62%, respectively for 7-hour13 a day. the
second treatment ( heat stress treatment). were the environment 61 temperature and relative? lnunidty were 39°C and 62% H. 1. , respectively for 7-houre a day. Each experimental treatment
lasted 11 days. The data were collected during the last 8 days . The results and conclusions obtained were as follows : Calciuru metmbolism : The averaged of total Ca intake in Friesian heifers were 26.011: 0.)6 and 25.42 1: 0.29 g/day under mild and hot climate. , respectively. There was a significant decrease (P 0 .01) in total Ca intake of 2.30%. Total Ca excretion average were 10.35 + 0 .53 and 12.98 + 0.47 g/day under wild and hot climate. respectively. The difference between the averages wn significo.nt increase (P 0.01) in total Ca excretion of 25 . 41~~ . The averages of ca balance were 15.70 + 0.66 and 12 .44+ 0.55 g/days. whereas t he retention were 60 .1 5% or 2 . 22 and 4f .91%+ 1.99 under mild and hot climates, respectively. Decreases in Ca balance and retention were 20 .80% end 18.70 %. respectively and such differences were significant (P 0.01).