الفهرس 
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Abstract
This study was carried out in the experimental farm of Animal Production Department, Faculty of Agriculture, Minia University, during July to September, 1999.
The main objective of this study was investigating the effects of increasing dietary energy level on some productive and physiological responses in dairy cows. Fat (Poultry grease) was the pure energy source used in this study. Dry matter intake, nutrients digestibility, milk and milk constituents yields and some physiological responses are parameters chosen to judge the effect of fat supplementation in dairy cows diet. The physiological responses observed are thermo-respiratory responses, hematological parameters, concentrations of some plasma metabolites and related hormones.
Six dairy Friesian cows were selected four in their second and two in their fourth lactation season after their peak of lactation, were served in this study. The average body weight of these cows 459.5±13.71 kg. Three diets were formulated to contain AFRC standards for maintenance and production (AFRC, 1993). Fat was added to the control diet in amounts that represent 10 and 15 % of AFRC metabolisable energy (ME) standards to develop the treatments T2 and T3, respectively. The control concentrate mixture (T1) contained 50 % yellow corn, 40 % wheat bran, 7 % soybean meal, 2 % calcium carbonate and 1 % sodium chloride. These experimental diets were iso-nitrogenous (l00 gram metabolisabe protein (MP) / kg DM) according to the tabulated values for each ingredient. Chopped wheat straw was the roughage source offered ad libitum in this study.