الفهرس 
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Abstract
The present study was conducted in the department of Animal Production, Faculty of Agriculture , Moshtohr, Banha, University. The experimental work was carried out at the Private Military Farm, Fayoum Governorate, located in part south of Nile Delta ( 30 ºN ), Egypt, during the period from December, 2007 to August, 2008 .
The total number of 8 bulls (4 Friesian and 4 buffalo bulls) at 3 – 4 years old with 500 –600 kg body weigh was used in the experimental work .
The present study was designed to define the effect of winter and summer seasons on body thermoregulation (rectal temperature, skin temperature , respiration rate and pulse rate ) of Friesian and buffalo bulls. Blood plasma components ( total protein , albumin, globulin, total cholesterol, urea - N , creatinine, aspartate-aminotransferase :AST, alanine aminotransferase: ALT, calcium , total phosphorus , sodium and potassium concentrations) were determined. Libido , semen characteristics ( semen –ejaculate volume , percentages of sperm motility , dead spermatozoa, sperm abnormalities, acrosomal damage of spermatozoa, sperm cell - concentration , total - sperm output and seminal pH ) were recorded. Histological changes in the testes, during winter and summer seasons were also recorded. Conception rates of cows and buffalo-cows during winter and summer seasons, were also assessed.
The obtained results can be summarized as follows : 1. Body thermoregulation
1.1. Rectal temperature (ºC), respiration rate (r.p.m.), skin temperature (°C) pulse rate (p.p.m.), were highly
significantly increased (P<0.01) in the summer as compared to winter season in both buffalo and Friesian bulls.
1.2. Rectal temperature was insignificantly higher, while respiration rate, skin temperature and pulse rate were significantly (P<0.01) higher Friesian than buffalo bulls. There were insignificantly differences in rectal temperature, skin temperature and pulse rate, while respiration rate was significant (P<0.05) as affected by individual buffalo and Friesian bulls.
2. Blood components
2.1. Total protein concentration (g/dl) in blood plasma increased significantly (P<0.01), while albumin and globulin concentrations insignificantly increased in the summer as compared to winter season either buffalo and Friesian bulls.2. Total protein globulin concentrations were significantly (P<0.01) higher, while albumin concentration was significantly (P<0.01), lower in buffalo than Friesian bulls. There were significantly (P<0.01) differences in blood plasma total protein, albumin and globulin concentrations as affected by individual buffalo and Friesian bulls.
2.3. Creatinine and urea-N concentrations (mg/dl) in blood plasma increased significantly (P<0.05 or P<0.01) in the summer as compared to winter season either buffalo or Friesian bulls.
2.4. Creatinine concentration was significantly (P<0.01) higher in Friesian than buffalo bulls, while urea-N concentrations was insignificantly higher in buffalo than Friesian bulls. There were significantly (P<0.01) differences in blood plasma Creatinine and urea-N concentrations as affected by individual buffalo and Friesian bulls.
2.5. Cholestrol concentration (mg/dl) in blood plasma increased significantly (P<0.01) in the winter as compared summer season either buffalo or Friesian bulls.
2.6. Cholestrol concentration was significantly (P<0.01) higher in Friesian than buffalo bulls there were significantly (P<0.01) differences in blood plasma cholestrol concentration as affected bu individual buffalo or Friesian bulls.
2.7. Aspartate-aminotransferase (AST) and alanine-aminotransferase (ALT) enzymes activity (U/l) in blood plasma increased significantly (P<0.05) in the summer as compared to the winter season either buffalo or Friesian bulls.
2.8. Aspartate-aminotransferase enzymes activity was significantly (P<0.01) higher, while alanine-aminotransferase enzymes activity was insignificantly lower in buffalo than Friesian bulls. There were significantly (P<0.01) differences in blood plasma AST and ALT enzymes activity was significantly (P<0.05) differences as affected individual buffalo and Friesian bulls.
2.9. Calcium, total phosphorus and potassium concentrations (mg /dl) in blood plasma increased significantly (P<0.01 and 0.05) while sodium concentration (mg/dl) decreased significantly (P<0.01 and 0.05) in winter as compared to summer season either buffalo or Friesian bulls.
2.10. Total phosphorus and sodium concentrations were significantly (P<0.01 and 0.05) higher in Friesian than buffalo bulls and potassium concentration was significantly (P<0.01 and P<0.05) higher in buffalo than Friesian bulls. However, calcium concentration was insignificant in buffalo than Friesian bulls. There were significantly (P<0.01 and 0.05) differences in blood plasma calcium, sodium, total phosphorus and potassium concentrations as affected by individual buffalo and Friesian bulls.
3. Libido and semen characteristics in buffalo and Friesian bulls
3.1. Libido
3.1.1.Libido of Friesian or buffalo bulls varied significantly ( P<0.01) by
the different seasons of the year, being shortest in the winter longest
in the summer seasons .
3.1.2.Libido of buffalo bulls was significantly ( P<0.01)longer than in Friesian bulls . Libido varied insignificantly according to individual buffalo or Friesian bulls.
3.2. Semen characteristics
3.2.1. Semen – ejaculate volume (ml) of Friesian and buffalo bulls during Winter season was significantly ( P<0.05) increased as compared to Summer season . Similarly, semen-ejaculate volume was significantly (P<0.01) higher in Friesian than buffalo bulls . The differences in semen- ejaculate volume due to the individual buffalo or Friesian bulls were significant (P<0.01).
3.2.2. Mass motility of Friesian and buffalo bulls during winter insignificantly. increased as compared to summer season. Mass motility was significantly (P<0.01) higher in Friesian than buffalo bulls. The differences in mass motility due to the individual buffalo or Friesian bulls were insignificant.
3.2.3. The percentage of sperm motility of Friesian and buffalo bulls during winter season were significantly (P<0.01) higher as compared to summer season . Similarly, the percentage of sperm motility was significantly (P<0.01) higher in Friesian than in buffalo bulls . The percentage of sperm motility changed significantly (P< 0.05) with the individual buffalo or Friesian bulls.
3.2.4.The percentage of dead spermatozoa of Friesian and buffalo bulls increased significant (P<0.01) during Summer season compared to winter one. Also, it significantly (P<0.01) higher in buffalo than Friesian bulls .The percentage of dead spermatozoa varied significantly (P<0.01) according to the individual buffalo or Friesian bulls.
3.2.5.The percentage of sperm abnormality of Friesian and buffalo bulls during Summer season were significantly (P<0.01) increased as compared to winter season . Similarly , the percentage of sperm abnormality was significantly (P<0.01) higher in buffalo than Friesian bulls . Also,it varied significantly (P<0.01) according to the individual buffalo or Friesian bulls.
3.2.6.The percentage of acrosomal damage of spermatozoa of Friesian and buffalo bulls during summer season were significantly (P<0.05) increased as compared to winter season . Similarly, the percentage of acrosomal damage of spermatozoa was significantly (P<0.01) higher in buffalo than Friesian bulls. While, it significantly (P<0.05) according to the individual buffalo or Friesian bulls.
3.2.7.Seminal hydrogen – ion concentration (pH) of Friesian and buffalo bulls during summer season was significantly (P<0.01) increased as compared to winter season . The pH value was insignificantly higher in buffalo than Friesian bulls . Similarly, there were insignificantly differences between Individual buffalo or Friesian bulls in pH value.
3.2.8. Sperm – cell concentration ( × 109 / ml ) of Friesian and buffalo bulls during winter season was significantly (P<0.01) increased as compared to summer season . Similarly, it was significantly (P<0.01) higher in Friesian than buffalo bulls. As well as between individual buffalo or Friesian bulls.
3.2.9. Total – sperm output ( × 109 / ejaculate ) of Friesian and buffalo bulls during winter season was significantly (P<0.05) increased as compared to summer season . Similarly, it was significantly (P<0.05) higher in Friesian than buffalo bulls. Also between the individual buffalo or Friesian bulls was significant (P<0.05).
4.Fertility rate(%) :
4.1. Fertility rate of Friesian bulls (%) :
The conception rate of Friesian cows naturally mated during summer was significantly (P<0.05) lower ( 74.50% ) than in winter ( 89.00 % ) season
4.2. Fertility rate of buffalo bulls(%) :
The conception rate of Buffalo - cows naturally mated during summer was significantly (P<0.05) lower ( 70.00% ) than in winter ( 84.16 % ) season .
5. Histological changes in the buffalo and Friesian bulls testes .
The testes of buffalo and Friesian bulls during winter season revealed highly active, highly vascularized, interstitial cells tissues and all stages of the spermatogenesis are present compared to summer season .
Conclusion
In conclusion , exposure of buffalo or Friesian bulls to heat stress during hot summer conditions affects deleteriously reproduction , biological function that include depression in total protein , enzymatic reaction and blood metabolism, especially when heat – stress is accompanied by high ambient humidity .Such changes results in impairment of the libido and semen characteristics and subsegment deer ease of fertilizing efficiency of bull spermatozoa . Reproductive performance in Friesian bulls is more efficiency in maintaining biological function, semen characteristics and fertility rate than buffalo bulls, under hot summer conditions.
Blood component and semen characteristics and their relationships with the histological changes in the testes might form the basis of rigorous of semen quality.
Libido of the bull undergoes seasonal fluctuations. However, very large variations were reported between individual bulls. It could be seen that , the buffalo and Friesian bulls under the present uniform managerial condition are able to produce semen during winter and summer seasons, but there are variation in the quality of semen produced. from the practical of view it might be recommended to use the semen characteristics for more accurate evaluation of semen quality at least periodically. Friesian and buffalo bulls semen quality and fertilizing ability were better in winter season ( short day light ) than summer season ( long day light ). So , bull semen could be collected and freezing during short day light for artificial insemination programmers to enhance of conception rate of cows or buffalo – cows under Egyption environmental conditions.