Development of Molecular Markers Based on the L1 Retrotransposon Insertion Polymorphisms in Pigs (Sus scrofa) and Their Association with Economic Traits

Molecular markers based on retrotransposon insertion polymorphisms (RTIPs) have great potential in studies of animal genetics and breeding. In this study, L1 RTIP markers were developed and evaluated by using microsatellite primers combined with L1 specific primers, and were further evaluated in four Chinese and three imported domestic pig breeds. Eight L1RTIP markers were obtained, and uneven distribution was observed among these breeds, with the Sujiang breed exhibiting the highest level of polymorphism with seven polymorphic sites, followed by Jiangquhai, Meishan, and Duroc with six, four, and four polymorphic sites, respectively. Both Landrace and Yorkshire pigs exhibited three polymorphic sites, while Chinese inbred Bama pig showed the lowest level of polymorphism with only one polymorphic site. Three polymorphic makers (L1-31-2, L1-31-5, and L1-31-11) were strongly associated with the economic traits in 462 Yorkshire pigs, with the L1-31-5+ genotype females had a significantly greater alive litter size (11.44 ± 2.80) compared with pigs with the L1-31-5– genotype (9.96 ± 2.89) (P < 0.05). L1-31-11– genotype pigs had significantly younger age at 100 kg of body weight (160.20 ± 10.26 days) than the L1-31-11+counter parts (162.47 ± 9.71 days) (P < 0.05). In summary, we demonstrated that it is feasible to develop markers based on L1 RTIP sin the pig, and these markers may have greater potential in the application of pig genetics and breeding compared to non-selective conventional breeding.