Direct response to selection for postweaning gain in the rat

Area of Science:

• Animal Genetics
• Quantitative Genetics
• Animal Breeding

Background:

• Previous selection for high 3-9 week gain in rats.
• Understanding the genetic basis of growth traits is crucial for animal breeding programs.

Purpose of the Study:

• To evaluate the effectiveness of selection for 3-9 week gain in rats.
• To assess the impact of environmental trends and natural selection on growth traits.

Main Methods:

• Selection for high (U line) and low (D line) 3-9 week gain over 13 generations.
• Use of randomly selected control lines (R and C lines) to estimate environmental trends.
• Relaxation of selection for six generations to detect natural selection effects.
• Estimation of genetic variances and bias in realized heritability using established statistical methods.

Main Results:

• A consistent negative environmental trend for 3-9 week gain was observed.
• Realized heritability estimates were not significantly different between U and D lines.
• Relaxation of selection showed no evidence of natural selection influencing the selected lines.
• Estimates of realized heritability variance were biased when using standard regression techniques compared to HILL'S formulae.

Conclusions:

• Selection for growth in rats is influenced by significant environmental trends.
• The effectiveness of selection for growth may be limited by genetic architecture and environmental factors.
• Accurate estimation of heritability requires accounting for potential biases in variance estimation.