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. Keywords: body condition score, close-up period, early lactation, Holstein cows, milk yield, peripartum behavior, primiparous dairy cows, udder morphology.