Divergent selection for yolk cholesterol in laying hens

Area of Science:

• Animal Science
• Genetics
• Biochemistry

Background:

• Yolk cholesterol concentration is a trait of interest in poultry breeding for both nutritional and production purposes.
• Understanding the heritability and response to selection for yolk cholesterol is crucial for genetic improvement programs.
• Previous studies have explored genetic variation in yolk cholesterol, but response to long-term divergent selection requires further investigation.

Purpose of the Study:

• To investigate the response to divergent selection for yolk cholesterol concentration in two distinct chicken populations.
• To estimate the realized heritability of yolk cholesterol in Leghorn and Athens-Canadian (AC) populations.
• To determine the effectiveness of selection in both increasing and decreasing yolk cholesterol levels.

Main Methods:

• Divergent selection for yolk cholesterol was applied for three (Leghorn) and four (AC) generations using individual and family records.
• Yolk cholesterol was analyzed using a colorimetric assay (Zlatkis et al., 1953) on pooled yolks from two eggs per hen at 28 weeks of age.
• Realized heritability was calculated based on the cumulative selection differential and the observed differences between high and low lines.

Main Results:

• Significant differences in yolk cholesterol concentration were achieved between high and low lines, with the largest divergence in the final generation.
• The low selection lines showed limited response, indicating a potential plateau or asymmetry in selection response.
• Realized heritability estimates ranged from 0.11 to 0.25, suggesting moderate heritability for yolk cholesterol.
• Heritability estimates on a within-line basis indicated that selection was more effective in increasing than decreasing yolk cholesterol.

Conclusions:

• Divergent selection can effectively alter yolk cholesterol levels in chickens, particularly in increasing the concentration.
• The lack of response in low lines suggests genetic asymmetry or limitations in reducing yolk cholesterol through selection.
• Selection for yolk cholesterol is most effective in the upward direction, implying different genetic mechanisms for increasing versus decreasing this trait.