Changes in connectedness over time in alternative sheep sire referencing schemes

Area of Science:

• Animal Breeding and Genetics
• Quantitative Genetics
• Livestock Production Systems

Background:

• Comparing estimated breeding values (EBVs) across different flocks is crucial for genetic improvement but can be biased.
• A reliable statistic is needed to quantify the genetic connectedness between flocks, assessing the risk of bias.
• Sire referencing schemes (SRS) are used to establish connections between flocks.

Purpose of the Study:

• To evaluate changes over time in selected connectedness measures.
• To determine the effectiveness of these measures in quantifying bias risk for EBV comparisons across production units.

Main Methods:

• Simulated sheep populations with varying flock sizes and sire referencing schemes (SRS).
• Data simulated for a single trait with known heritability.
• Connectedness measured using average prediction error correlation (r(ij)) and prediction error variance of differences (PEVD) for flock genetic means and lamb EBVs.

Main Results:

• Flock r(ij) increased linearly with SRS implementation and plateaued upon discontinuation.
• Lamb r(ij) showed rapid increases with SRS but substantial decreases if SRS was stopped.
• Flock r(ij) demonstrated a consistent, albeit nonlinear, relationship with bias across simulation scenarios.

Conclusions:

• Average prediction error correlation (flock r(ij)) is a reliable measure of genetic connectedness.
• Benchmark levels of flock r(ij) (0.05 and 0.10) are suggested to minimize bias in EBV comparisons.
• These benchmarks help producers assess and manage the risk of comparing animals across different flocks.