Identification of genetic markers for productive life in commercial sows

Escalating replacement rates and production costs warrant attention on sow productive life (SPL). Increasing average SPL by one-tenth of 1 parity would result in an annual revenue increase of over $15 million in the United States. Research in model organisms has revealed conserved genes and gene pathways that lead to longer lifespan. The most prominent gene pathways are those involved in growth, most notably genes in the IGF pathway that serve to mimic the response of caloric restriction. The objective of this research was to test the hypothesis that these well conserved genes and gene pathways could also play a role in SPL, even though the productive life of sows is both a measure of longevity and their reproductive performance. Preliminary research on 3 distinct populations of over 2,000 animals suggested that several genes were associated with components of SPL. Genetic markers were then analyzed against the corresponding records of the sows for reproductive and longevity traits using a validation population of 2,000 commercial females. Right censored data were used to test associations of genetic markers with survival to defined time points. Three distinct models of survival analysis were implemented using nonparametric estimates of the survival distribution in a sequential order, using a parametric accelerated failure time model with a Weibull distribution of the error term, and a Cox proportional hazards model, which is a semiparametric model that uses an unspecified baseline hazard function. The genetic markers CCR7 and CPT1A were significantly associated (P < 0.05) with survival using the nonparametric model and tended (P < 0.1) toward significance using the parametric and semiparametric models with significantly different effects (P < 0.05) between some genotype classes. Genetic markers for MBL2, IGFBP3, and WARS2 also tended (P < 0.1) toward significance for survival traits, but were not consistent. Mixed model analyses were used to determine the associations of these genetic markers with reproductive traits. The genetic markers for IGFBP1, MBL2, CPT1A, CCR7, SLC22A5, and ACE were significantly (P < 0.05) associated with at least 1 reproductive trait. These results show that molecular markers should be considered for use in marker-assisted selection to improve SPL.