الفهرس 
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Abstract
The aim of this investigation is to study the effect seasonal variations in Egypt on hematological parameters, reproductive and metabolic hormones of Egyptian buffalo-cows. This study lasts one year extended from December 2009 to November 2010 and conducted on sixty buffalo-cows. Monthly selected group of 5 buffalo-cows which were at estrus phase then blood sampling through tail vein puncture in the 2nd day after natural service, divided in two samples one with anticoagulant for hematological analysis and the other without anticoagulant for serum separation. Results of this investigation revealed that the highest atmospheric temperature was in hot summer (32.61±1.12 Co) versus to (26.18±1.67 Co) in spring and (19.92±0.70 Co) in winter season, while the highest relative humidity % was in winter season (43.50±1.60%) versus to (32.50±2.29%) in summer season. The rise in temperature-Humidity index from (63.73±1.29) in winter to (78.53±1.58) in summer indicates sever heat stress which associated with significant reduction in total red blood cell count (3.20±0.15×106), hemoglobin concentration (8.83±0.43 g/dl), packed cell volume (30.73±0.12%), lymphocytes % (40.66±2.33 %)serum progesterone hormone concentration (0.56±0.03 ng/mll), estradiol17-B concentration (16.8±0.64 ng/ml), triiodothyronin (T3) concentration (2.33±0.33 ng/ml) and thyroxin hormone (T4) concentration (21.66±1.66 ng/ml), while hot summer resulted in significant increase in mean cell volume (96.55±2.25 fl), mean cell hemoglobin (30.81±1.33 pg), total white blood cell count (10.63±0.97×103), neutrophils % (49.66±2.33%), serum prolactin hormone (PRL) concentration (23.45±1.72 ng/ml) and cortisol hormone concentration (4.47±0.33 ng/ml) compared to winter season. There was no significant seasonal variation in mean cell hemoglobin concentration (MCHC). It was concluded that In Egypt there was a seasonal variation in atmospheric temperature, relative humidity, temperature humidity index (THI) and the rise in THI above the upper critical level (72 units) for lactating buffalo-cows in Egypt is the major constraint on buffalo-cows hematological parameters and hormonal secretion whish affects animal reproduction. Hence we should improve climatic conditions in side the dairy farm to eliminate or reduce summer infertility