Effect of body condition score loss during the transition period on metabolism, milk yield and health in Holstein cows.

Introduction: This study aimed to investigate the impact of perinatal body condition score (BCS) and its subsequent loss on postpartum performance and health outcomes in dairy cattle. Material and Methods: A total of 156 cows were randomly selected, and blood samples were collected at -21, 0, 7, 14, 21, 28 and 50 days relative to calving. Milk yield and disease incidence in dairy cows were recorded after calving. These cows were subsequently categorised into three groups based on BCS loss during the transition period: a no-BCS-loss (maintained BCS) group (M, 0 < BCS loss ≤ 0.25), low-BCS-loss group (L, 0.25 < BCS loss ≤ 0.5), and high-BCS-loss group (H, BCS loss > 0.5). Results: All groups experienced a decline in BCS from 21 days prepartum through 50 days postpartum (P-value < 0.01). Cows in the H group had the highest levels of non-esterified fatty acids, beta-hydroxybutyrate, total cholesterol, aspartate aminotransferase, albumin, malondialdehyde and leptin (P-value < 0.05). Concomitantly, total antioxidant capacity, as well as the levels of insulin and glucose, were the lowest in group H (P-value < 0.05). Plasma concentrations of Ca, P, Mg and K, urea nitrogen and total bilirubin were not significantly influenced by BCS loss (P-value > 0.05). Cows in the M group were less likely to develop ketosis, mastitis, retained placenta, displaced abomasum and metritis than those in the H group, and cows in the H group produced the lowest milk yields (P-value < 0.05). Conclusion: These observations collectively indicate that BCS loss is associated with measurable changes in energy balance, liver function, oxidative stress, daily milk production and disease incidence during the transition period.