Reproductive traits are difficult to select for due to low heritability and late expression of the traits. However, genomic information can be used to detect quantitative trait loci (QTL) for these traits, which may improve the accuracy of selection. In addition, acclimation strategies for gilts that enter the herd can affect reproductive performance. The objectives of this study were to estimate genetic parameters, to identify QTL associated with reproductive traits in commercial crossbred sows, and to determine the impact of acclimation on reproductive performance. Performance data from 1 to 4 parities and genotypes (40K SNPs) were available from 21 commercial farms on Large White x Landrace sows from 7 breeding companies (PigGen Canada). Traits analyzed included total number of piglets born (TB), number of piglets born alive (NBA), number of stillborn piglets (SB), number of mummified piglets (MUM), number of piglets weaned (NW). In addition, gilt average daily gain during acclimation (ADG) and PRRS vaccination status (Vx) were available. Genetic parameters (heritabilities) were estimated using ASReml v.4 and genome-wide associations were performed in GenSel. Heritabilities for TB ranged from 0.12  0.04 (parity [p] 1) to 0.21  0.04 (p2), NBA from 0.05  0.06 (p4) to 0.15  0.04 (p2), SB from 0.08  0.04 (p2) to 0.11  0.05 (p3), MUM from 0.00  0.00 (p3) to 0.05  0.03 (p1), NBD from 0.06  0.06 (p4) to 0.10  0.04 (p1), and NW 0.00  0.00 (p1) to 0.27  0.07 (p4). There were significant effects of ADG on TB and NBA for parity 1. In parity 1, regions associated with TB, NBA, and SB explained 13.9% (chromosome [SSC]1 and SSC6), 10.8% (SSC2 and SSC10), and 20.9% (SSC13) of the genetic variance (GV), respectively. For parity 2, regions associated with SB, MUM, and NW explained 3.9% (SSC11), 3.8% (SSC4), and 10.7% (SSC15) of the GV. In parity 3, regions associated with NW accounted for 4.7% (SSC7) of the GV. In parity 4, regions associated with TB and NW explained 10.6% (SSC13) and 15.8% (SSC13) of the GV, respectively. These results indicate that reproductive traits are lowly heritable. Greater ADG during acclimation positively affected TB and NBA during parity 1. The GWAS revealed QTL that correspond to corpus luteum number, teat number, age at puberty, TB, NBA, SB, and MUM, all traits that are related to reproduction. Keywords: genome-wide association study, reproductive performance, gilt acclimation

Cassandra Ferring, Benny Mote, Philip Willson, PigGen Canada, John Harding, Graham Plastow, Jack Dekkers, Nick Serão

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume Biology - Reproduction 1, , 757, 2018
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