Age-related changes and seasonal variations in the daily sperm production of the stallion

ABSTRACT

Fifty-six testes were collected from 28 Arab and native stallions [aged 3 to 18 years] along a complete annual cycle to determine the influence of age and season on the daily sperm production [DSP] by a quantitive histological technique. Overall, mean values for testicular measurements, percentage of seminiferous tubules [SNT%], corrected number of spermatids and diameter of SNT/stage I cross-section were given in the text. Estimates of 4.39 x 10[9] sperm/tcstis/day, 8.77 x 10[9] sperm/ stallion/day and 28.45 x 10[6] sperm/g parenchyma were noted, highly significant [P < 0.01] increase with age in these traits was evident up to 13 years old stallions, where peak values of 5.30 x 10[9], 10.60 x 10[9] and 33.67 x 10[6] for the foregoing parameters were achieved. On the other hand, testicular weight, parenchymal weight, number of spermatids per stage I tubule cross-section and DSP/g accounted for 64%, 63%, 67% and 86% of the variation in the DSP/testis, respectively. Age-related changes in the above mentioned parameters were also scrutinized. The onset of breeding season [December-May] in Arab and native horses was associated with a significant increase in testicular weight [13%], parenchymal weight [14%], diameter of SNT/ stage I cross-section [8%], corrected number of spermatids/stage I tubule cross-section [15.%], DSP/testis [27%] and DSP/stallion [27%]. The production of sperm [per testis/day or stallion/day] was lowest [3.66 x 10[9] vs 5.01 x 10[9] and 7.33 x 10[9] vs 10.03 x 10[9]; P<0.01] in the non-breeding season, averaging only 73% of the DSP in the breeding season. Therefore, stallions are capable of producing significantly more spermatozoa [2.70 x 10[9] additional sperm/stallion/day] in the breeding season and could supply sufficient numbers of sperm for insemination of more mates at this time