Mitigating the effect of seasonality on sow reproductive performance using genetic selection

Abstract Text:

The objective of the study was to estimate variance components and inbreeding effect for sow reproductive performance considered as different traits according to the season of conception. Reproductive and pedigree data were obtained for 18,648 Landrace litters from nucleus farms in Texas (n=1) and North Carolina (n=2). Traits included number born alive (NBA), total number born (TNB), number born dead (BD) and fetal loss (FL) calculated as BD/TNB.  Season of conception was defined as Winter (December – February), Spring (March – May), Summer (June – August), and Fall (September – November). Variance components and genetic correlations were estimated with gibbs1f90 using a multiple-trait model with trait by season represented in the model. The model included fixed effects of contemporary group (herd by year) and parity and random additive genetic effect of sow. For the inbreeding estimates, level of inbreeding was also included in the model as a covariate. Heritability estimates were greatest for NBA, TNB and BD for conception in Summer months with estimates of 0.198, 0.208 and 0.165, respectively, and for FL for Spring conception with an estimate of 0.172. Heritability estimates were lowest for Spring conception for NBA (0.107) and TNB (.086), for Fall conception for BD (0.122) and for Summer conception for FL (0.138). Genetic correlations were greatest for NBA (0.946) and TNB (0.934) in Spring and Winter, and the relationship between Spring and Fall for BD (0.987) and PWM (0.935). Genetic correlations were lowest for NBA (0.794) and TNB (0.733) for Spring and Summer, for Spring and Winter for BD (0.817) and for Fall and Winter for FL (0.823). The estimates and standard error of inbreeding depression for each trait by season are shown in Table 1. The results suggest that NBA, TNB, BD and FL should be treated as different traits according to season of conception, and summer performance appears to be determined by a different genetic background compared to the other seasons. Selection for increased performance during the summer months may be a more effective method to mitigate seasonal infertility than selection for performance across the year. It is also suggested that increased inbreeding may be especially detrimental for sows conceiving during the Summer and Fall season.

Table 1. Estimates and standard error of inbreeding depression for each trait by season

Trait	Spring	Summer	Fall	Winter
NBA	-0.03 (0.02)	-0.05(0.02)	-0.06(0.02)	-0.02(0.02)
TNB	-0.04(0.03)	-0.04(0.02)	-0.06(0.02)	-0.02(0.02)
BD	-0.0037(.01)	0.01(0.0092)	-0.0019(0.0096)	-0.0066(0.0091)
FL	0.0002(0.0008)	0.0005(0.0007)	0.0005(0.0009)	-0.0001(0.0006)

Keywords: genetics, seasonality, sow