HERITABILITY OF SCROTAL CIRCUMFERENCE IN ONE- AND TWO-YEAR-OLD BULLS OF DIFFERENT BEEF BREEDS

Over an 8-yr interval, (1975–1982) scrotal circumference (SC) was measured on 4557 1-yr-old beef bulls from 1796 sires and eight breeds. Measurements were taken upon completion of a 140-d growth performance test. During the period 1977–1983, SC was measured on 7835 2-yr-old beef bulls from 2570 sires and six breeds. Two-year-old bulls were measured during reproductive examinations at spring bull sales. All SC measurements were adjusted for fixed effects of location-year and age, and heritability estimates were calculated within-breed using a paternal half-sib analysis. Heritability estimates for the SC trait in Angus, Charolais, horned Hereford, polled Hereford, Shorthorn, Simmental, Limousin and Maine-Anjou breeds in 1-yr-old bulls were 0.22 ± 0.20, 0.46 ± 0.14, 0.89 ± 0.17, 0.83 ± 0.26, 1.01 ± 0.31, 0.63 ± 0.19, 0.94 ± 0.29 and 0.59 ± 0.22. Heritability estimates for SC in 2-yr-old bulls of the first six breeds were 0.00 ± 0.21, 0.60 ± 0.25, 0.57 ± 0.07, 0.65 ± 0.10, 0.69 ± 0.34 and 0.20 ± 0.24. Owing to the small number of sires or sons within sires for some breed-age groups and the exclusion of some sources of variation in the statistical model, the estimates of heritability may not be precise and should be used to indicate approximate levels of heritability for a particular breed. Key words: Heritability, testicular size, scrotal circumference, beef bulls