Selection for feed efficiency using the social effects animal model in growing Duroc pigs: evaluation by simulation

Area of Science:

• Animal breeding and genetics
• Quantitative genetics
• Livestock production

Background:

• Traits in group-housed animals can be analyzed using the social effects animal model (SAM), offering more complete genetic correlation structures than the traditional animal model (AM).
• Previous studies reported unfavorable genetic correlations between average daily gain (ADG) and backfat thickness (BF) in Duroc pigs.

Purpose of the Study:

• To evaluate the effectiveness of the SAM in genetic evaluations for ADG and BF to indirectly improve feed conversion ratio (FCR).
• To assess if the SAM could mitigate unfavorable genetic correlations between ADG and BF.

Main Methods:

• Estimated genetic and non-genetic correlations between BF, ADG, and FCR in 1144 pigs using Bayesian methods and the SAM.
• Utilized stochastic simulation to analyze responses to selection indexes combining direct genetic effects (DGE) and indirect genetic effects (IGE) for ADG and BF.

Main Results:

• Genetic parameters for ADG, BF, and FCR were estimated, with total genetic variance ratios to phenotypic variance ranging from 0.63 to 0.93.
• Using SAM for genetic evaluations resulted in a worse average economic response compared to AM predictions.
• Observed economic response was primarily due to a reduction in BF, not an improvement in FCR.

Conclusions:

• Social genetic effects are significant in the studied traits, but their effective use in pig breeding programs for indirect FCR improvement remains challenging.
• Correlations between IGE and DGE were insufficient to overcome unfavorable DGE correlations, and SAM genetic parameter estimates had large errors.
• These limitations penalized the average response achieved with SAM compared to AM.