Genetic analysis of reproductive traits and antibody response in a PRRS outbreak herd1

Abstract

Porcine reproductive and respiratory syndrome (PRRS) is the most economically significant disease impacting pig production in North America, Europe, and Asia, causing reproductive losses such as increased rates of stillbirth and mummified piglets. The objective of this study was to explore the genetic basis of host response to the PRRS virus (PRRSV) in a commercial multiplier sow herd before and after a PRRS outbreak, using antibody response and reproductive traits. Reproductive data comprising number born alive (NBA), number alive at 24 h (NA24), number stillborn (NSB), number born mummified (NBM), proportion born dead (PBD), number born dead (NBD), number weaned (NW), and number of mortalities through weaning (MW) of 5,227 litters from 1,967 purebred Landrace sows were used along with a pedigree comprising 2,995 pigs. The PRRS outbreak date was estimated from rolling averages of farrowing traits and was used to split the data into a pre-PRRS phase and a PRRS phase. All 641 sows in the herd during the outbreak were blood sampled 46 d after the estimated outbreak date and were tested for anti-PRRSV IgG using ELISA (sample-to-positive [S/P] ratio). Genetic parameters of traits were estimated separately for the pre-PRRS and PRRS phase data sets. Sows were genotyped using the PorcineSNP60 BeadChip, and genome-wide association studies (GWAS) were performed using method Bayes B. Heritability estimates for reproductive traits ranged from 0.01 (NBM) to 0.12 (NSB) and from 0.01 (MW) to 0.12 (NBD) for the pre-PRRS and PRRS phases, respectively. S/P ratio had heritability (0.45) and strong genetic correlations with most traits, ranging from -0.72 (NBM) to 0.73 (NBA). In the pre-PRRS phase, regions associated with NSB and PBD explained 1.6% and 3% of the genetic variance, respectively. In the PRRS phase, regions associated with NBD, NSB, and S/P ratio explained 0.8%, 11%, and 50.6% of the genetic variance, respectively. For S/P ratio, 2 regions on SSC 7 (SSC7) separated by 100 Mb explained 40% of the genetic variation, including a region encompassing the major histocompatibility complex, which explained 25% of the genetic variance. These results indicate a significant genomic component associated with PRRSV antibody response and NSB in this data set. Also, the high heritability and genetic correlation estimates for S/P ratio during the PRRS phase suggest that S/P ratio could be used as an indicator of the impact of PRRS on reproductive traits.

Host genetics of response to porcine reproductive and respiratory syndrome in nursery pigs

“…This proposition is further strengthened by results from an outbreak in a reproductive sow herd reported by Serão et al (2014), which found high favorable genetic correlations of S:P ratio measured by ELISA ∼46 days after the outbreak with reproductive performance (litter size, number stillborn, number mummies) during the outbreak. Indeed, further studies indicated moderate genomic prediction accuracies for PRRS S:P ratio using SNPs located within two genomic regions on SSC7 that had large effects on S:P ratio, while the rest of the genome showed limited predictive ability (Serão et al, 2016).…”

A major gene for host response to porcine reproductive and respiratory syndrome is not unfavorably associated with overall performance under nonchallenging conditions in commercial pig lines

“…Prior to this study, information regarding the effect of WUR under nonchallenging conditions was limited to the effect of WUR on reproductive performance in gestating sows (Serão et al, 2014) and growth rate in finishing pigs (Abella et al, 2016). In general, results from the current study are consistent with those reported by Serão et al (2014), who showed that prior to a natural PRRS outbreak, the effect of WUR on reproductive performance of commercial gestating females was nonsignificant for all traits analyzed, except number weaned. For this trait, an unfavorable association of WUR with reproductive performance was detected, where the B allele was associated with significantly fewer piglets weaned (Serão et al, 2014).…”

Genome-wide association study of growth and body composition traits in Brangus beef cattle

“…The GV% explained by each lead SNP was assessed by fitting it separately from the candidate window in the GWAS models (e.g. Serão et al, 2014). Significance of every lead SNP was evaluated in an animal model with ASReml v3.0 (Gilmour et al, 2009), by fitting the single SNP genotype (0/1/2 or AA/AB/BB) as a fixed class effect (e.g.…”