Environmental factors affecting services per conception in Hanwoo cows

Services per conception (SPC), i.e., the number of artificial inseminations (AIs) required for conception, is a key reproductive indicator in cattle.We quantified SPC in Hanwoo cows and evaluated the primary environmental sources of variation, focusing on the insemination setting.After quality control, 1,141 AI-to-calving records from the Hanwoo Research Center were analyzed; only normal single-calf calvings were retained, and records requiring ≥ 5 AIs were excluded.Cows were classified into either the hormone-treated group (HT), or the natural estrus group (NE).Differences in SPC across factors were tested using linear models and analysis of variance (ANOVA).SPC was lower in HT than in NE (1.38 ± 0.756 vs. 2.06 ± 0.785; p < 0.001).In HT, inseminator effects were significant (p = 0.026), whereas parity, AI year, and season were not (p > 0.05).In NE, primiparous cows had a lower SPC than multiparous cows (p < 0.001); the SPC was higher in March -August than in September -February (p < 0.05).Overall, the environmental sources of variation in SPC were not uniform across insemination settings, with parity and seasonal effects evident mainly under natural-estrus-based AI.Given the low heritability of reproductive traits and the strong influence of management and contemporary group effects on SPC, analyses of Hanwoo cows should account for insemination settings and systematically adjust for key environmental factors to avoid biased genetic effect estimates.