Abstract
Semi-isolated populations of two regions with varying amounts of semen exchange between them, both one-directional and reciprocal, were simulated from a basic mixed model that included fixed effects of herd and region of stud and random effects of sires within region of stud. The population consisted of 1,364 first-lactation daughters of 50 sires in 184 herds. Increasing the amount of semen exchange more accurately estimated the genetic difference between regions, and reciprocal exchange was more desirable than one-directional exchange. When genetic difference between region of stud was ignored, biases in prediction of sire effects increased while error variances of prediction remained relatively constant as semen exchange between regions intensified. Ignoring genetic relationships among sires increased error variances of prediction of sire proofs by 8.7 to 11.9% depending upon amount of semen exchanged.
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