A bivariate quantitative genetic model for a threshold trait and a survival trait

Area of Science:

• Quantitative genetics
• Animal breeding
• Statistical genetics

Background:

• Functional traits in animal breeding, such as disease resistance, conformation, calving difficulty, and longevity, can be modeled as threshold or survival traits.
• Understanding genetic and environmental correlations between these traits is crucial for effective breeding programs.

Purpose of the Study:

• To develop and implement a bivariate quantitative genetic model for analyzing a threshold trait and a survival trait simultaneously.
• To estimate the genetic and environmental correlations between these traits.
• To assess the potential for correlated responses in breeding programs.

Main Methods:

• A bivariate quantitative genetic model was developed, incorporating a Weibull log-normal animal frailty model for the survival trait.
• A Bayesian approach using Gibbs sampling was employed, augmenting model parameters with unobserved liabilities for the threshold trait.
• Specific sampling methods including Metropolis-Hastings and adaptive rejection sampling were used for parameter updates.

Main Results:

• The simulation study confirmed the accuracy of the model, with estimated posterior distributions closely matching true values.
• Analysis of dairy cattle calving difficulty and longevity revealed significant genetic variation for both traits.
• A moderately favorable additive genetic correlation (mean = 0.37, 95% CI = 0.11–0.61) was found between calving difficulty and longevity.

Conclusions:

• The developed bivariate model effectively analyzes correlated threshold and survival traits in animal populations.
• Significant genetic variation exists for both calving difficulty and longevity in dairy cattle.
• Selection for improved calving difficulty or longevity is likely to yield beneficial correlated responses in the other trait, supporting integrated breeding strategies.