Disease-induced variability of genetic correlations: ascites in broilers as a case study

Area of Science:

• Animal genetics and breeding
• Avian pathology and physiology
• Quantitative genetics

Background:

• Ascites syndrome in broiler chickens is a significant production disease with complex genetic underpinnings.
• Understanding the interplay between productivity, disease susceptibility, and environmental factors is crucial for effective breeding strategies.
• The etiology of ascites involves a physiological cascade resulting from an inadequate oxygen supply relative to metabolic demand.

Observation:

• A study involving 2,788 chickens in an ascites-challenging environment analyzed mortality, pathology, performance, and physiological traits.
• Genetic analysis revealed opportunities for selection against ascites expression, with mortality and pathology traits representing a common characteristic.
• An unexpected negative genetic correlation (-0.26) was observed between productivity and ascites incidence in the overall population.

Findings:

• Direct selection against ascites pathology proved more effective than selection based on growth or blood gas traits.
• Reanalysis of the undiseased subpopulation revealed a positive genetic correlation (0.29) between productivity and ascites, contrasting the overall population.
• The discrepancy was attributed to the environmental sensitivity and complex interactions between productivity, disease susceptibility, and disease occurrence.

Implications:

• The lability of genetic correlations between productivity and disease traits necessitates careful consideration of environmental factors in breeding programs.
• The findings suggest that genetic correlations for production-related diseases are inherently sensitive to environmental conditions, complicating index selection.
• The demonstrated mechanism is generalizable to other production diseases, highlighting the need for integrated approaches in genetic improvement.