Análisis de los factores que afectan el largo de gestación sobre bovinos de raza “Wagyu”

Gestation length (GL) is a key reproductive indicator in beef cattle breeding, as it determines the calving interval and the possibility of achieving one calf per cow per year. Wagyu cattle, a breed originally from Japan valued for its meat quality, were introduced to Uruguay in 2003. Two years later, the breed was incorporated by the Rogberg family at the "El Oriental" farm (Soriano), where it has been the subject of several production studies; however, GL in this breed had not previously been studied under Uruguayan production conditions. The objective of this study was to analyze the variability of GL in purebred Wagyu cattle and their crosses with Holstein and Angus at this farm, evaluating the effect of maternal genotype, year of calving, and calf sex on gestation duration and birth weight. A total of 624 gestation events recorded between 2017 and 2025 were analyzed, corresponding to 416 cows (purebred Wagyu and F1 and F2 crosses with Holstein or Angus) and 31 Wagyu bulls, with all conceptions obtained through fixed-time artificial insemination. GL was calculated as the difference between calving date and conception date. A mixed model was fitted including year of calving, maternal genotype, calf sex, and birth weight as fixed effects, and dam identity as a random effect, estimated by restricted maximum likelihood. To analyze birth weight, the same model was fitted without birth weight as a fixed effect. A second model, with sire as a random effect, allowed estimation of GL heritability and its genetic correlation with birth weight. Mean GL was 286.2 ± 5.5 days (range 261-299 days), 3 to 5 days longer than reported for Uruguayan beef cattle. Year of calving and calf sex significantly affected GL (males gestated on average one day longer than females), while maternal genotype showed no significant effect. In contrast, all three variables significantly affected birth weight. Birth weight was positively and significantly associated with GL, although it explained only a small fraction of its total variation. Estimated GL heritability was 0.224 ± 0.106, and a non-significant trend toward a negative genetic correlation between GL and birth weight was observed. The results indicate that GL in Wagyu cattle raised in Uruguay is longer than in traditional beef breeds, with direct implications for the margin available to achieve one calf per cow per year. Maternal genotype does not determine gestation duration, a result consistent with the proposed theoretical framework, while crossbreeding allows birth weight to be managed without altering the expected calving date, facilitating reproductive planning at herd level.