Genetic parameters for age at puberty and associated traits in swine

The objective of this study was to estimate variance components for age at puberty and associated traits in swine. Multigenerational records were compiled from composite Landrace × Large White animals (n=4,994) reared at the North Carolina Department of Agriculture Tidewater Research Station. Animals were part of a four generation selection experiment for age at puberty. Females (n=2,428) were reared in a curtain-sided building with fully slatted floors and natural ventilation. Sprinklers activated when temperatures reached 27^oC. Gilts were placed in pens of 15 (0.84 m² per pig). At 130 d of age, gilts were exposed to mature boars for 7 min daily and estrous behavior recorded. Estrous detection continued for 90 d. Puberty was defined as first observed standing reflex in the presence of a boar. Female reproductive traits included: age at puberty (AP), length of estrus at puberty (LEN1), estrous length at second estrus (LEN2), puberty weight (PUBWT), vulva width at puberty (VW1) and vulva width at second estrus (VW2). Production traits included: piglet birth weight (BWT), piglet weaning weight (WWT), loin eye area (LEA), backfat depth (BF) and weight at 178 d of age (WT). Variance components were averaged over all animal models where the trait appeared in ASReml. Models included generation and sex as fixed effects, and random effects of maternal environment and animal. Covariates were fit for reproductive traits (age at boar exposure), LEA and BF (WT), and WT (age). Heritability estimates for AP, LEN1, LEN2, PUBWT, VW1, VW2, BWT, WWT, LEA, BF and WT were 0.31, 0.18, 0.15, 0.29, 0.28, 0.41, 0.21, 0.12, 0.42, 0.43 and 0.39, respectively. Common litter effects for AP, PUBWT, VW1, BWT, WWT, LEA, BF, and WT were 0.08, 0.04, 0.05, 0.03, 0.29, 0.02, 0.10 and 0.11, respectively. Genetic and phenotypic correlations between AP with LEN1, LEN2, PUBWT, VW1, VW2, BWT, WWT, LEA, BF and WT were -0.15, -0.38, 0.84, 0.12, 0.13, -0.11, -0.16, 0.26, -0.30 and -0.46, and -0.03, -0.11, 0.81, 0.30, 0.18, 0.01, 0.02, 0.14, -0.20, and -0.18, respectively. Results indicate maternal effects exist for weaning weight, age at puberty, backfat and growth rate. Selection for reduced age at puberty in swine would generate gilts that: have a longer length of estrus and are lighter at puberty yet faster growing.