Screening of three-way crossbred combination and genetic effect analysis of the SNP in the CLPG gene in meat sheep.

In order to promote the rapid development of the meat sheep industry, a three-way crossbred combination experiment was carried out with Australian White, Dorper, and Charollais sheep as terminal male parents and the elite F1 hybrids of Australian White  $\times$  Small-tailed Han (Han), Dorper  $\times$  Han, and Charollais  $\times$  Han as female parents, which was based on the screening of a two-way crossbred combination in meat sheep. The growth performance of six groups of three-way crossbred combinations and Han lambs was measured and analyzed, and the effect of a polymorphism in the CLPG gene on the growth performance of three-way crossbred lambs was also studied. The results showed that under the same rearing conditions, weight at 3 and 6 months of age and average daily gain from birth to 3 months and from 3 to 6 months of age were all the largest for Australian  $\times$  (Charollais  $\times$  Han) crossbred lambs. They were significantly or extremely significant different from the other three-way crossbred combinations and Han lambs ( $P<0.05$ , $P<0.01$ ). The body height, body length, chest girth, and cannon bone circumference at 3 months of age and body length, chest girth, and cannon bone circumference at 6 months of age were also the largest for Australian  $\times$  (Charollais  $\times$  Han) crossbred lambs. Among them, body length, chest girth, and cannon bone circumference at 3 months of age were significantly different from the other three-way crossbred combinations and Han lambs ( $P<0.05$ ), and body length, chest girth, and cannon bone circumference at 6 months of age were significantly or extremely significant different from the other three-way crossbred combinations and Han lambs ( $P<0.05$ , $P<0.01$ ). The potential genetic effects of the CLPG gene on the growth performance indicators of three-way crossbred lambs showed that a mutation site ( $g$ .232 $C$   $>$   $T$ ) of this gene had two genotypes: CC and CT. Among them, the data of body weights and body sizes from CT genotype individuals at birth, 3 months old, and 6 months old were significantly higher than those of CC genotype individuals, and some indicators showed significant or extremely significant differences ( $P<0.05$ , $P<0.01$ ), suggesting that higher growth performance was observed in individuals with $T$ alleles. To sum up, the crossbred combination of Australian  $\times$  (Charollais  $\times$  Han) could be suggested as the optimal choice. The $T$ allele of the CLPG gene showed potential advantages in the performance of meat production in meat sheep. Based on the current results, we recommend that the offspring of Australian  $\times$  (Charollais  $\times$  Han) with the $T$ allele should be preferentially utilized for meat sheep production.