Fixed or Random Contemporary Groups in Genetic Evaluations

Computer simulation was used to analyze the effect of considering contemporary groups as fixed (Model [1]) or random (Model [2]) on genetic value predictions. Eighty-eight types of populations were generated from four different ratios of error to contemporary group variances, two types of association (random and nonrandom) among sires' breeding value and contemporary groups, and 11 contemporary group sizes. Nonrandom association among sires and contemporary groups resulted in a positive correlation (.6) between them. Both sires' additive value and contemporary groups were considered as random variables in the simulation process. Prediction error variance, mean squared error, correlation between predicted and real breeding values, and rank: correlation were measured.