Relationship between live weight and robustness in Holstein cows: productive, reproductive, and health analysis in a mixed dairy grazing system

Abstract

The objective of this study was to evaluate the robustness of Holstein cows (n=82) in a mixed pasture-based dairy system and its relationship with body weight (BW). Robustness was defined as the animal's ability to maintain adequate productive, reproductive, and health performance throughout its life. The cows, managed in the same group, were classified into four BW groups: <600 kg (class 1, n=21), 600–650 kg (class 2, n=25), 650–700 kg (class 3, n=17), and >700 kg (class 4, n=19). The variables analyzed included productive [milk yield (MY)], reproductive [calving interval (CI), calving-to-conception interval (CCI), services per conception (SPC)], and health parameters (percentage of animals with at least one episode of mastitis during their lifetime). The data were analyzed using BW class as a fixed effect, with age at the current lactation and date of last calving as covariates. Continuous variables were analyzed using linear models, while categorical variables were assessed using generalized linear models assuming a binomial distribution. Statistical significance was considered at P≤0.05. Multiple comparisons were performed using Tukey’s test. Cumulative MY in the current lactation was significantly higher in class 3 compared to class 4 (P<0.05), while the remaining classes showed intermediate values. No significant differences were observed for any reproductive variables (P>0.10). In contrast, mastitis incidence—both lifetime and in the current lactation—increased significantly with BW, being highest in class 4 (P<0.05). In conclusion, BW was associated with milk yield and mastitis incidence but not with reproductive performance. These findings provided relevant insights for decision-making regarding cow selection and management in pasture-based dairy systems.