Variasi Fenotipik dan Keberulangan Sifat Semen pada Sapi Pejantan Limousin dan Simmental Terkait Umur, Musim, dan Frekuensi Ejakulasi

Artificial insemination programmes depend on high-quality semen from superior bulls, yet integrated analyses that jointly consider age, season, and ejaculation frequency and relate them to trait repeatability remain scarce for Limousin and Simmental bulls under tropical conditions. This study analysed phenotypic variation and repeatability of semen traits and the effects of these factors. Secondary fresh-semen records of four bulls (two Limousin, two Simmental) from the Singosari National Artificial Insemination Centre, Indonesia, 2021–2024 (1,456 ejaculate records) were analysed for semen volume, sperm concentration, total sperm concentration, abnormality, and motility. Breed, age group, season, ejaculation frequency, and their interactions with breed were tested using a factorial linear mixed model with bull as a random effect, and repeatability was estimated as the intraclass correlation before and after adjustment. Age significantly affected volume, concentration, total concentration, and motility; season affected concentration, total concentration, and abnormality; ejaculation frequency had no significant main effect. Repeatability was moderate to high for sperm concentration (0.41 adjusted) but low for other traits. Limousin bulls produced higher volume, whereas Simmental bulls showed superior sperm quality. The novelty lies in integrating these factors with repeatability estimation, identifying sperm concentration as the most repeatable indicator for bull evaluation in tropical AI centres.