Genotype × Nutritional Environment Interactions in Grazing Beef Cow-Calf Systems: Evidence for Crossbreeding and Reproductive Efficiency from Breeding to Weaning

Reproductive efficiency determines the biological and economic sustainability of grazing beef cow–calf systems, yet the extent to which nutritional conditions modify genotype-associated reproductive performance remains unclear. This review critically examines the relationships among crossbreeding, heterosis, herbage allowance, and reproductive outcomes across the breeding-to-weaning continuum. A structured narrative synthesis evaluated 36 publications, classified as direct reproductive genotype × nutritional environment (G × N) evidence (Level I, n = 2), genotype and crossbreeding evidence (Level II, n = 14), nutritional evidence (Level III, n = 9), and mechanistic or supportive evidence (Level IV, n = 11). Across the reviewed studies, crossbreeding was frequently associated with favorable reproductive and maternal outcomes, although the magnitude and consistency of these associations varied among breed combinations, production environments, and reproductive endpoints. Greater forage availability and more favorable nutritional status were also associated with improved body condition and reproductive outcomes in some studies, consistent with established metabolic and endocrine mechanisms. However, these genotype- and nutrition-associated patterns do not, by themselves, establish causal effects or G × N interactions. Only two publications directly evaluated reproductive G × N within an analytical framework, both originating from a shared grazing research program. One reported stage-specific interaction evidence, particularly during the calving-to-weaning period, while the other included an interaction term without separately reporting its estimate. Nutritional effects varied with physiological stage, parity, body condition, and previous nutritional exposure. These findings emphasize that pregnancy rate alone incompletely represents reproductive efficiency because subsequent reproductive and calf losses influence cumulative productivity. Calves weaned per cow exposed, supplemented by calf weight weaned, provides a more comprehensive endpoint. Independent, longitudinal factorial studies across diverse genotypes and grazing environments are needed to establish the reproducibility, biological significance, and management implications of reproductive G × N interactions.