Influence of age, breed lines and season on boar sperm motility and morphology under tropical conditions

Sperm morphology assessment is essential for maintaining reproductive efficiency and profitability on farms. In tropical countries and smaller-scale farms, the assessment of sperm morphology of the doses used in artificial insemination is not routinely carried out; therefore, its analysis and standardization are necessary. This study evaluated the influence of age, season, and genetic line on sperm morphology in breeding boars under tropical conditions. The study was conducted on commercial farms in the northern region of Costa Rica from 2019 to 2023, with sampling during both the dry and rainy seasons. Sixty-five boars and 312 ejaculates representing Duroc, Landrace, Pietrain, and Pietrain × Duroc genetic lines were analyzed. Animals were classified by age at collection into three groups according to age at the time of collection: < 24 months (G1, n = 19), 24–48 months (G2, n = 26), and > 48 months (G3, n = 33); some animals were analyzed and classified into different groups. Morphology was assessed by Trumorph® fixation and visual examination using a light microscope at 400× magnification. The percentage of sperm morphological abnormalities varied significantly by year, season, and genetic line (P < 0.05). The Pietrain line showed the highest average abnormality frequency, whereas the rainy season exhibited the greatest proportion of abnormal sperm (P < 0.05). In conclusion, season and genetic line significantly influenced sperm morphology in breeding boars. Standardization and validation of morphological assessment are necessary in semen production centers and commercial pig farms.