Effect of extended close-up period duration on peripartum behavior, udder morphology, body condition score, and early lactation yield in primiparous Holstein cows.

Background and Aim: The transition period is a critical phase in dairy cows, characterized by profound physiological, metabolic, and behavioral adaptations that influence health, welfare, and productivity. The duration of the close-up period, typically the final phase of the dry period before calving, plays a key role in preparing cows for parturition and subsequent lactation. However, the optimal length of this period remains debated, particularly in primiparous Holstein cows, where parity-specific responses may differ from those in multiparous animals. This study aimed to evaluate the effects of extending the close-up period beyond the conventional duration on peripartum behavior, calving characteristics, reproductive performance, body condition score (BCS), udder morphology, and early lactation yield. Materials and Methods: A prospective cohort study with retrospective grouping was conducted on 14 clinically healthy primiparous Holstein cows monitored from four weeks prepartum to four weeks postpartum. Based on actual close-up duration, cows were classified into Period A (18-26 days; n = 7) and Period B (27-35 days; n = 7). Behavioral and ordinal data were analyzed using the Mann-Whitney U test, while continuous variables such as gestation length and calving-to-first insemination interval were analyzed using a General Linear Model (GLM). Milk yield was assessed using both a GLM and a linear mixed-effects model with repeated-measures, with Bonferroni adjustment. Statistical significance was set at p < 0.05. Results: Behavioral parameters did not differ significantly between groups (p > 0.05). Period B cows exhibited a longer gestation length (279.0 ± 3.28 vs. 271.3 ± 4.17 days; p = 0.041) and a tendency toward a shorter calving-to-first insemination interval (p = 0.052). BCS was significantly higher in Period B at calving (p = 0.024) and at Week 4 postpartum (p = 0.004). Udder morphology improved in Period B, with higher udder position (p = 0.018) and vascularization scores both prepartum (p = 0.031) and postpartum (p = 0.012). Milk yield was markedly higher in Period B (36.80 ± 1.34 vs. 26.80 ± 0.96 L/day; p < 0.001), with consistent superiority across all postpartum weeks (p < 0.012). Conclusion: Extending the close-up period to 27-35 days in primiparous Holstein cows enhances physiological preparedness, improves udder morphology, and significantly increases early lactation milk yield without adversely affecting calving characteristics. These findings support the implementation of a moderately extended close-up period as a practical management strategy to optimize transition performance and productivity.