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Abstract Bos indicus-Bos taurus crosses have been effectively used in many production environments globally. Substantially higher amounts of hybrid vigor have been reported in these F1 crosses as compared with those involving only Bos taurus or only Bos indicus breeds. However, for many years, and in many environments, “unusual” aspects of calf growth have been documented among these crosses. Among F1 crosses, Bos indicus-sired calves (Bos indicus x Bos taurus) have birth weight 8 to 12 kg heavier than contemporary Bos taurus-sired calves (Bos taurus x Bos indicus); additionally, pronounced sexual dimorphism occurs where males may weigh 5 to 10 kg more than females from Bos indicus sires (Bos taurus dams) but 1 kg or less from Bos taurus sires (Bos indicus dams) in both natural service and embryo transfer calves. These reciprocal differences have been reported for fetal and placentome size mid gestation. Reciprocal differences in birth weight have also been reported among backcrosses and F2 calves, and also exist for longer gestation length from Bos indicus sires (Bos taurus dams). Increased birth weight and gestation length occur when more Bos indicus is present in the sire vs. the dam, and when Bos indicus influence is inherited through the sire vs. the dam. There is speculation that sex-specific genomic imprinting may be involved for reciprocal birth weight differences that are analogous to mouse interspecific crosses for litter weight. Reports of hybrid vigor retention among inter se matings after the F1 have been variable historically, and this variation may relate to how the foundational F1 parents were produced (Bos indicus- vs. Bos taurus-sired). Breed-of-origin haplotype on BTA5 has been shown to affect heifer pregnancy and rebreeding among F2 Nellore-Angus cows where Nellore-derived haplotypes had much lower performance compared with Angus-derived and hybrid haplotypes. Disproportionate calf sex has been reported among reciprocal F2 Nellore (Bos indicus)-Angus (Bos taurus) with 66.6% male calves from Nellore x Angus F1 sires. When retrospectively evaluating historical literature for reciprocal crosses, it appears that several instances occur with disproportionate calf sex percentage, and this phenomenon warrants further study. The extent that potential reciprocal differences may affect post-weaning growth and carcass traits has not been widely evaluated. Recent investigations have shown reciprocal F1 differences for some cell-mediated immune responses regarding T-lymphocyte proliferation, but no differences for humoral response. There needs to be additional research that completely characterizes the X chromosome of Bos indicus and Bos taurus origins and their roles for multiple production traits. There also needs to be more investigation of non-additive and parent-of-origin effects in genetic evaluations of Bos indicus-Bos taurus composites, particularly with desired first-generation breed percentage. Improved utilization of Bos indicus cattle and crosses will be instrumental in meeting global dietary protein demands.
Herring et al. (Sun,) studied this question.