Degree of connectedness among groups of centrally tested beef bulls
The degree of connectedness among test groups (TG) of bulls tested in central evaluation stations from 1988 to 2000 in Ontario, Canada, was evaluated using the following methods: average prediction error variance of the difference between estimated breeding values (PEVD), variance of estimated differences between test group effects (VED), connectedness rating (CR), and total number of direct genetic links between test groups (GLT). The model used in the analysis included the effects of breed and TG (fixed) and animal (random). PEVD was assumed the most adequate measure of connectedness and results from the alternative methods VED, CR, and GLT were compared against it. Models to predict the average PEVD of pairs of TG and the average PEVD of each TG with all other TG on the basis of VED, CR, and GLT were developed. Results from all measures of connectedness indicated an unfavorable trend in the degree of connectedness after 1994. The average PEVD of pairs of TG can be better predicted on the basis of the model that includes GLT. The average PEVD of each TG with all other TG can be better predicted on the basis of models that include either CR or GLT. Connectedness among TG of centrally tested beef bulls can be adequately assessed for specific pairs of TG or overall for each TG with all other TG using GLT. Key words: Accuracy, central test, genetic evaluation, harmonic mean