Relationships of genomic estimated breeding values for age at puberty, birth weight, and growth during development in normal cyclic and acyclic gilts.

ABSTRACT

Managing replacement gilts to reach optimal body weight and growth rate for boar stimulation and first breeding is a key component for sow reproductive longevity and producer profitability. Failure to display pubertal estrus remains a major reason that gilts are culled from the herd. Puberty is metabolically gated so evaluating phenotypic and genetic relationships between birth weight and growth traits with age at puberty and acyclicity can provide valuable insight for efficient gilt development. Data on a litter of origin of the gilt, average daily gain at different stages of development, and age at puberty were available for age-matched cyclic (n = 4,861) and acyclic gilts (prepubertal anestrus, n = 578; behavioral anestrus, n = 428). Genomic estimated breeding values were predicted for each trait using genomic best linear unbiased prediction. Primiparous sows produced more acyclic gilts than multiparous sows (P < 0.05). Accounting for effects of parity and litter size, prepubertal anestrus gilts were heavier at birth and behaviorally anestrus gilts grew faster during the finisher period compared to cyclic gilts (P < 0.05), reflecting possible prenatal programming that negatively affects optimal pubertal development and antagonistic effects between adolescent growth and expression of estrus of gilts from first parity sows. Regression of phenotypic age at puberty with lifetime growth rate (birth to selection) showed a negative linear relationship whereas genomic estimated breeding values showed a negative quadratic relationship indicating that gilts with the least and greatest growth are less optimal as replacements. The slopes of these relationships are small with low negative phenotypic (r = -0.06) and genetic correlations (r = -0.13). The addition of data from acyclic gilts did not substantially change the estimates for genetic relationships between growth and pubertal onset. Although this study identified differences in birth weight and growth rate between cyclic and acyclic gilts the genetic relationships are weak, suggesting that genetic selection for these traits can be achieved separately. Avoiding the smallest and largest gilts in a cohort born to first parity sows could result in gilts with optimal development and reduce the proportion of replacement gilts that are acyclic.

Failure to display pubertal estrus is major reason replacement gilts are culled from the herd. Two types of prebreeding estrus failure are delay in attaining puberty due to sexual immaturity known as prepubertal anestrus (PPA) and silent ovulation without signs of estrus known as behavioral anestrus (BA). For efficient gilt development, it is important to understand what contributes to these acyclic phenotypes. Comparison of birth weight and growth rate in age-matched cyclic, PPA, and BA gilts showed that PPA gilts were heavier at birth and BA gilts grew faster during the finisher period, reflecting negative effects of larger birth weight and faster growth on sexual maturity and behavioral estrus. The genetic relationship between growth and puberty onset indicated that gilts with the least and greatest growth rates are less optimal as replacements. A selection criterion to avoid the smallest and largest gilts in a cohort could result in gilts with optimal development for boar stimulation and reduce the proportion of acyclic gilts. This management strategy would be most effective if targeted to first parity sows.