Evidence of differentiation and population structure in Charolais cattle of Mexico.

Charolais is one of the most important beef cattle breeds in the world. In Mexico, it was introduced almost a century ago, and it has been suggested that particular breeding management and genetic material origin have caused a process of divergence among the current population. By a high-density SNP array genome-wide analysis, this study aimed to assess the proposed differentiation and population structure of local populations by genetic distances and structure approaches, and a European Charolais sample was included as a reference population. The differentiation statistics indicated that local populations exhibit moderate divergence, confirming a significant differentiation process between northeastern and northwestern Charolais populations (Fst≥ 0.043, D≥ 0.031). These results were strongly supported by PCA and structure analysis. Genetic isolation and low genetic flow between populations and divergent origins of introduced genetic material (i.e., semen) are likely the main drivers of the outcomes. Some implications are discussed.

Environmental factors and ram influence litter size, birth, and weaning weight in Saint Croix hair sheep under semi-arid conditions in Mexico.

This study was conducted to evaluate the effects of season, year of lambing, parity, and the effect of ram on litter size, birth, and weaning weight through 8 years. Data of 4078 lambs sired by 21 rams and 1072 ewes were analyzed by a lineal model. There was a significant effect (P < 0.05) of lambing number on litter size and birth weight, but not on weaning weight (P > 0.05). For litter size, the lowest numbers were obtained on the first lambing ewes (1.21 ± 0.03) and the highest ones inewes starting from the fourth lambing (1.69 ± 0.04). Lowest body weights were found in lambs born from first lambing ewes (3.01 ± 0.1 kg) and the highest ones in lambs born from the second (3.14 ± 0.1) to the fifth (3.15 ± 0.2) lambing ewes. The lambing breeding season had a significant effect on weaning weight: the highest weaning weights were recorded in lambs born in spring (12.70 ± 0.20 kg) and the lowest ones in those born in summer (11.93 ± 0.20 kg). Lambing year had a significant effect (P < 0.05) on litter size and weaning weight, since the values of both traits improved through the years. Effect of ram was significant (P < 0.05) for each of the traits considered: there were differences up to one lamb per litter, also differences up to 1.5 kg for birth weight and up to 6.5 kg for weaning weight among rams. In conclusion, these results indicate that environmental conditions are important source of variation in litter size, birth, and weaning weight in hair sheep under semi-arid climate.