Relación entre condición corporal y la eficiencia reproductiva en vacas de cría de diferentes genotipos

Reproductive efficiency is a key factor in the productivity of cattle breeding systems, particularly under extensive conditions where forage availability is variable and affects reproductive performance. Body condition score is among the most widely used indicators, as it is closely associated with pregnancy probability and calving interval. In this context, crossbreeding can contribute to improved productive and reproductive efficiency through heterosis. This study aimed to analyze the relationship between body condition score at calving and reproductive efficiency, measured by calving interval and calving percentage, in beef cows of different genotypes managed on native pasture in Uruguay. Records from the breeding herd of the Bernardo Rosengurtt Experimental Station (EEBR) of the Faculty of Agronomy, University of the Republic, covering the period 2006–2017, were used. Cows of the Angus (AA), Hereford (HH), and their reciprocal crosses (AH and HA) genotypes were analyzed. The variables considered were body condition score at calving (BCC), first calving interval (FCI1), average calving interval (FCI), and calving percentage. Effects evaluated included forage availability, category, cow and bull genotype, and month and year of calving. Data were analyzed using non-parametric tests and tests of independence with R software (version 4.5.1). Significant differences in body condition score at calving were observed in association with forage availability, category, cow genotype, and month and year of calving (p < 0.001). Crossbreeds (AH and HA) had higher mean BCC scores (3.84–3.85) than purebreds (3.67–3.71), with less internal variability. In the first calving interval, no significant differences were observed according to the cow's genotype, although differences were observed according to the bull's genotype, with HA having the shortest average (460 days) and AA the longest (509 days). In the average calving interval, crossbred genotypes showed shorter values ​​(432–434 days) compared to purebred genotypes (460–461 days). Calving percentages were high and varied among categories, with values ​​ranging from 86.4% to 94.7% in heifers and from 85.9% to 91.3% in cows, showing a favorable trend toward crossbred genotypes. Body condition at calving is a relevant variable in the analysis of the herd's reproductive efficiency, evaluated through calving percentage and calving interval. The crossbred genotypes (Hereford × Angus and Angus × Hereford) showed a trend toward greater reproductive efficiency, associated with slightly higher body condition scores at calving and a lower body condition score required to achieve the same calving percentage, compared to the purebred genotypes. Calving intervals did not differ significantly between genotypes, being primarily associated with other environmental and management factors. These findings suggest that crossbreeding could contribute to improved reproductive regularity and efficiency in extensive grazing systems on native pastures, which should be evaluated in future studies with greater control of environmental and management variables.