Exploration of the Exogenous Male Yak Introduction Breeding Model and its Effects on Tibetan Small-Sized Family Farms

A total of three family farms including Village No. 9 in Nima township, Nerong Naqu County (NQA); Village No. 11 in Nima township, Nerong Naqu County (NQB); and Yare township, Gegi County, Ali District (GJ) from three ecology yak populations (EYP) were selected for this study to identify the most optimized mode of exogenous male adult yak introduction (EMI) within EYP for solving the inbreeding problem caused by the small-scale yak husbandry system. Exogenous adult male yaks from the same EYP with different proportions (100% to NQA, 50% to NQB, and 0% to GJ) were introduced, and 10 microsatellites were used to detect the genetic diversity of these populations before (in 2017) and after (in 2019) the introduction of exogenous adult male yaks (EMI). Results showed that the divergence between the observed and the expected heterozygosity of the NQA and NQB populations was reduced in 2019, while the number of markers significantly deviating from Hardy–Weinberg equilibrium (P<0.05) and FIS (inbreeding coefficient) within populations decreased compared with that in 2017. In contrast, the FIS of GJ population without EMI continued to increase (from 0.011 to 0.033) over the years 2017 to 2019. Moreover, genetic differences between the populations (Pairwise Fixation index, FST) showed that EMI increased the genetic divergence between populations. Overall, this study shows that the introduction of exogenous male adult yaks not only effectively reduces the degree of population deviation from equilibrium but also decreases the inbreeding level within the population within a few generations. This study also provides a valuable management model for stable yak production on small sized family farms