Effects of body condition score and parity on reproductive and health outcomes in Hanwoo cows.

This study examined the interactive effects of body condition score (BCS) and parity on reproductive performance and health outcomes in Hanwoo cows. A total of 511 cows were grouped by parity, specifically, heifers (parity 0), multiparous cows (parity 1-4), and older cows (parity ≥ 5), and by BCS, specifically, under-conditioned (UC, BCS < 2.5), adequate (AD, BCS 2.5-3.5), and over-conditioned (OC, BCS ≥ 4.0). Pregnancy rates varied significantly according to parity and BCS. OC heifers had the highest conception rate (95.8%), but also exhibited increased rates of maternal (17.4%) and calf (8.7%) health issues. Multiparous cows maintained high fertility even at low BCS, although heavier male calves were associated with greater calving difficulty in the UC group. Among older cows, the AD group had the most favorable outcomes, whereas the UC group failed to conceive. Gestation was longest in heifers with AD BCS, suggesting sensitivity to maternal condition. Calf birth weight was heaviest for male calves born to UC multiparous cows, who also faced the greatest calving difficulty. Calf and dam health outcomes were poorest in OC cows, particularly heifers. Logistic regression analysis revealed significant negative interaction effects between low BCS and heifer status, indicating that the conception likelihood was reduced in these groups. The impact of BCS was strongly modulated by parity. In summary, OC may benefit fertility in heifers but increases perinatal risk, while multiparous cows tolerate lower BCS at increased calving difficulty. Older cows benefit most from maintaining a moderate BCS. These findings emphasize the need for parity-specific nutritional strategies to improve reproductive performance and herd health in Hanwoo cattle.