In a stallion breeding-soundness examination, testicular volume may be estimated either from total scrotal width or by measuring the height, width and length of both testes. This study aimed to determine whether testicular morphometric parameters obtained by ultrasonography fluctuate throughout the year, and whether these variations affect semen quality and hormone production in stallions located at low latitudes in the Southern Hemisphere. Eight healthy light-breed stallions were evaluated every 15 days for 1 year, encompassing the breeding (October-April) and non-breeding(May-September) seasons. Assessments included testicular ultrasonographic measurements, semen quality, hormonal profiling and thermographic evaluation. Testicular morphometric parameters, particularly total testicular volume and testicular width, exhibited seasonal variation, with greater values observed during the breeding season. A moderate correlation was identified between total testicular width and total testicular volume, indicating that width contributes to testicular volume variation. Despite the increase in testicular volume during the breeding season, total sperm number per ejaculate remained stable throughout the year, and only subtle seasonal changes were observed in seminal and hormonal parameters. Minor and total sperm defects increased during the breeding season, coinciding with higher ambient temperature, the temperature-humidity index (THI) and scrotal surface temperature. Cortisol concentrations were higher during the non-breeding season, suggesting physiological adaptation to environmental conditions. These findings indicate that stallions maintained at low latitudes exhibit limited reproductive seasonality and suggest that seasonal changes in testicular morphometry are more closely associated with thermoregulatory adaptations than with marked alterations in spermatogenic activity.
Braga et al. (Mon,) studied this question.