Características seminais em garanhões da raça Crioula: influência da sazonalidade e idade

Abstract

Semen plays a crucial role in reproductive biotechnologies. Understanding the response of sperm production to climatic variations is of utmost importance to optimize reproductive processes, improve reproductive efficiency, and preserve genetic traits. This study aimed to evaluate the influence of seasonality and age of Criollo stallions on seminal characteristics commonly assessed in routine evaluations. Retrospective data from 2,390 ejaculates, obtained from 104 stallions over a 7-year period, were analyzed in the southern region of Rio Grande do Sul, Brazil (latitude -31.709137 and longitude -52.457724). The seminal characteristics analyzed included volume, vigor, motility, sperm morphology, and sperm concentration per mL. Total sperm count (TSPZ) and total motile sperm count (TSPZM) were subsequently calculated. Stallions were categorized into three age groups: young (2–4 years), mature (5–15 years), and elderly (16–25 years). Statistical analyses included analysis of variance (ANOVA) and Tukey's test, or Kruskal-Wallis and Dunn's test for non-parametric variables. Polynomial regression was performed for TSPZ and TSPZM according to age groups. Age had a significant influence (p<0.05) on TSPZ and TSPZM, with the highest values observed in mature stallions (6.4±3.4x10⁹ and 4.8±3.1x10⁹, respectively), followed by young stallions (5.7±3.0x10⁹ and 5.7±3.0x10⁹), and the lowest values in elderly stallions (5.3±3.1x10⁹ and 4.0±2.8x10⁹). Season alone did not show a direct relationship with seminal variables; however, there was an interaction between season and age for concentration, TSPZ, and TSPZM (p<0.05). Young and mature stallions showed lower total sperm counts in winter and higher values in summer. In contrast, elderly stallions showed a reduction in total motile sperm counts during summer. In polynomial regression, only young stallions showed a correlation with TSPZM (r²=-0.031, p<0.001). Regarding seasons, elderly stallions presented lower TSPZM values during summer, whereas young and mature stallions showed higher mean TSPZ and TSPZM during summer. These results confirm the relationship between age, season, and seminal characteristics in Criollo stallions.