Longitudinal analysis of weight showed little relationship with age at puberty in gilts

Abstract

Continued selection for increased gilt body weight could negatively impact selection for age at puberty (AP) in gilts. The purpose of this study was to compare the genetic potential for growth to that for reducing age of puberty in swine. Females utilized (n = 1,079) were produced over a 6-yr period from a population developed to determine the impact of energy restrictions and genetic influences on sow development and longevity. From 120 to 235 d of age, BW was collected every 14 d and attainment of puberty tested. Age at puberty was defined as the first observed standing estrus in the presence of a mature boar. All females were genotyped with the Porcine SNP60K BeadChip and genotypes were used to construct a genomic relationship matrix. Univariate (AP), repeatability (BW), and random regression (BW; RR) models were fitted. Univariate analysis included the fixed effects of contemporary group (CG) and age at first boar exposure, and random direct additive and common litter effects. Repeatability analysis included the fixed effects of CG and random effects of direct additive, common litter, and permanent environmental (PE) effects. Random regression analysis included fixed effects of CG, and random direct additive, common litter, and PE effects. Proportion of phenotypic variation due to direct additive and common litter variance for AP were 0.33 and 0.06, respectively. Proportion of phenotypic variation due to direct additive, common litter, and PE variance estimated from the repeatability model for BW were 0.26, 0.11, and 0.40, respectively. Proportion of phenotypic variation due to direct additive, common litter, and PE variance estimated from the RR for BW ranged from (mean) 0.19 to 0.30 (0.27), 0.08 to 0.31 (0.19), and 0.42 to 0.62 (0.50), respectively. Direct additive correlations between test days for BW from RR ranged from 0.30 to 0.99. Rank correlations between estimated breeding values (EBV) for AP and BW from the RR were near zero across all age points ranging from -0.03 to 0.09. Rank correlations were higher (0.63) when BW was considered at the age at which puberty was reached. Correlations between AP and BW EBV from the repeatability model were low (-0.11). Growth appears to be less related to AP than previously reported, suggesting the need to either directly measure AP or investigate alternative indicator traits. Selecting gilts with most desirable BW EBV alone would not result in improvement in AP, at least in the current population.