Thirty Egyptian healthy female buffalo cows were used in this study. The experimental animals were divided into two similar groups (15 in each group).  control (G₁, non-cooling) and cooling group (G₂). Each group was divided into three sub-groups (5 in each),control, supplemented with zinc methionine or niacin.Source of cooling water was the main concrete tank of the farm where temperature of the water ranged between 19-21 C0 at time of cooling. Results show that skin and rectal temperature degrees, and respiration rate decreased under cooling system. Cooling system decreased (P<0.05) haemoglobin concentration and packed cell volume (PCV %), while the effect of feed supplements was not significant. Zinc and Niacin supplements increased (P<0.05) total protein concentration in blood plasma only under cooling system. Albumin and glucose concentrations in blood plasma were not significantly effected. Blood urea nitrogen concentration in blood plasma decreased (P<0.05) in feed supplements under cooling groups. All groups of under cooling system showed shorter days open compared with those under non-cooling system, being the highest with Zn and Niacin supplementats. Zn and Niacin supplementation increased (P<0.05) conception rate under cooling system than those in the under non-cooling system.