Relationships of scrotal circumference (SC) with body weight (BW) and backfat thickness (FT) as measured from scanograms were studied. A total of 935 observations on growing multibreed synthetic beef bulls on a postweaning performance test were available from a commercial herd for this study. Significant breed group, period and group × period interaction effects were noted on SC, BW and FT. BW and SC increased significantly during the test in all breed groups, while FT showed no change in three breed groups. Repeatability pooled across groups for SC was estimated as 0.72; 0.66 after adjusting for BW. Significant correlations were noticed between SC and BW within each breed group. Partial correlations between SC and BW at constant FT were not different from gross correlations. Linear regression coefficients of SC on BW were significant in all groups and showed heterogeneity among groups but not between periods within groups. Adjustments of SC for BW should, therefore, be breed group specific. BW alone accounted for considerable variation in SC, from 38 to 76%. Simple correlation coefficients between SC and FT were low and significant in only two groups. A significant but low positive relationship was noted between SC and FT at constant BW in a group fed a high-concentrate diet during the postweaning gain period, but there was no relationship in four other groups. Results indicated that the method of adjusting SC for FT as an indirect way of adjusting for scrotal fat was not satisfactory. Key words: Bulls, scrotal circumference, growth
