Genetic Variance Estimation over Time in Broiler Breeding Programmes for Growth and Reproductive Traits

Area of Science:

• Animal Genetics
• Quantitative Genetics
• Breeding Programs

Background:

• Directional selection in breeding programs can deplete genetic variation, threatening long-term sustainability.
• Previous studies relied on small experimental populations, limiting insights into real-world commercial breeding lines.
• Understanding genetic variance dynamics is vital for maintaining genetic progress in livestock.

Purpose of the Study:

• To monitor changes in genetic variance for body weight (BWT) and hen-housed egg production (HHP) in a large commercial broiler line over 23 years.
• To compare different statistical methods (REML, Gibbs sampling) for estimating variance components.
• To assess the impact of selection and drift on genetic variation over time.

Main Methods:

• Analysis of a large dataset (2,059,869 records, 2,062,112 animals) from a commercial broiler line.
• Estimation of variance components using sliding overlapping windows with frequentist (REML) and Bayesian (Gibbs sampling) methods.
• Application of "double trait covariances" analysis to confirm variance stability.

Main Results:

• Genetic variance for BWT and HHP showed marginal fluctuations but a slight overall increasing trend from 1999-2001 to 2020-2022.
• Heritability estimates followed a similar pattern, with slight increases observed for both traits.
• Double trait covariance analysis confirmed the maintenance of genetic variances, with high genetic correlations (>0.86 for BWT, >0.82 for HHP) between consecutive periods.

Conclusions:

• Genetic parameters in this commercial broiler line tended to increase slightly over time, suggesting resilience to selection-induced loss of variation.
• The findings indicate that factors like novel mutations might compensate for selection pressure, maintaining genetic variance.
• Continuous monitoring of genetic variance is essential for the long-term success of breeding programs.