Abstract
The Booroola fecundity gene (FecB) has a mutation that was found to increase the ovulation rate and litter size in Booroola Merino sheep. This mutation is also associated with the fecundity of small-tail han (STH) sheep, an important maternal breed used to produce hybrid offspring for mutton production in China. Previous research showed that the FecB gene affects reproduction in STH sheep, based on litter size records. However, the effects of this gene on estrus, ovulation, and endocrine characteristics in these sheep remain unclear. Here, we analyzed the traits mentioned earlier and compared them among the three FecB genotypes of STH ewes using estrus synchronization. Overall, 53 pluriparous ewes were selected from among 890 STH ewes and subjected to FecB genotyping for experiments to characterize estrous and ovulation rates. FecB heterozygous (+B) ewes presented an earlier onset of estrus (42.9 ± 2.2 h) and a shorter estrous cycle (17.2 ± 0.2 days) (P ≤ 0.05). The ovulation rates increased with the increasing copy number of the B allele (P ≤ 0.01). Ovulation time showed no significant differences among the three FecB genotypes. The serum concentrations of follicle-stimulating hormone (FSH), luteinizing hormone, estrogen (E2), and progesterone (P4) were measured in 19 of the ewes. Serum concentrations of E2 and FSH dramatically varied around the time of behavioral estrus. In FecB mutant homozygous (BB) ewes, E2 concentration had two peaks, which were higher (P ≤ 0.05) than those of ++ genotypes. FSH concentration of BB ewes was higher (P ≤ 0.05) than that of the ++ ewes just after estrus. The expression of the estrogen receptor 1 (ESR1) gene in the +B genotype was higher than in the other genotypes. Based on the data for the reproductive performance of STH ewes with the three FecB genotypes, our study suggests that the development of follicles in ewes with the B allele is dependent on the response to FSH regulated by E2 in the early stage. +B ewes, exhibiting moderate ovulation and litter size and a shorter estrous cycle, can be highly recommended in sheep crossbreeding systems for commercial mutton production. Moreover, this study provides useful information to conserve better and use the genetic resources of STH sheep in China.
Highlights
IntroductionThe FecB gene, called BMPR1B (bone morphogenetic protein receptor type 1B), was initially identified in prolific Booroola Merino sheep
The FecB gene, called BMPR1B, was initially identified in prolific Booroola Merino sheep
Genetic analysis of the FecB gene in this study showed that the three FecB genotypes are still not fixed in this Small-tail han (STH) sheep population collected from a population set aside for conservation
Summary
The FecB gene, called BMPR1B (bone morphogenetic protein receptor type 1B), was initially identified in prolific Booroola Merino sheep. These sheep have a mutation (A746G) in the coding region of the FecB gene, leading to the substitution of glutamine for arginine in the protein [1,2,3,4,5]. The FecB gene was shown to significantly affect litter size in STH sheep and other Chinese sheep breeds [16]. Because of their excellent reproductive performance, STH sheep are widely used as the female parent in crossbreeding to improve the production efficiency of commercial mutton sheep.
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