Scrotal Circumference in Yearling Hereford Bulls: Adjustment Factors, Heritabilities and Genetic, Environmental and Phenotypic Relationships with Growth Traits

Abstract

Field data on 4,233 yearling Hereford bulls were analyzed using fixed and mixed model least-squares procedures to examine factors affecting scrotal circumference; determine appropriate adjustment factors; and study genetic, environmental and phenotypic relationships among scrotal circumference and growth traits. Scrotal circumference was affected by postweaning feed level; contemporary group/feed level; age of dam; and covariates age, weight and height. Of the three covariates, weight had the greatest effect, and any factor which caused an increase in weight tended to increase scrotal circumference. Quadratic effects of age, weight, height and age X age of dam interaction effects were significant or approached significance, but were of minor importance. Large contemporary group effects suggested the need for expressing scrotal circumferences as trait ratios or as deviations from contemporary group means. Scrotal circumference adjustment factors recommended for yearling Hereford bulls were .026 cm X d-1 of age and .8, .2 and .1 for sons of 2-, 3- and 4-yr old dams, respectively. Heritability of weight-adjusted scrotal circumference was .46 +/- .06 compared with .49 +/- .06 for age-adjusted scrotal circumference, indicating considerable additive genetic variation for relative scrotal size. Correlations between scrotal circumference and growth traits were moderate to high. The genetic correlation between scrotal circumference and yearling weight was the highest of these at .44 +/- .16. Potential implications of this relationship are discussed.

Factors Affecting Body Weight, Scrotal Circumference Hip Height and their Relationships with Birth Weighl Preweaning and Postweaning Gains in Young Bulls

“…Among the independent variables, BW had the lowest associations with final WT, SC and HHT and, therefore, was least useful in predicting the dependent variables. The low correlation between SC and BW in young beef bulls is in agreement with the genetic correlation estimate of 0.18 as reported by Bourdon and Brinks (1986). Brinks (1994) reported that growth of bulls from birth to yearling was positively correlated with SC, but BW had low association with SC.…”

“…The equations explained 92 and 67 per cent of variation in final feedlot weight and scrotal circumference, respectively. These results confirmed the evidence that growth of bulls from birth to yearling age and testicular development were highly correlated, at least in beef bulls which had undergone postweaning performance testing (Bourdon and Brinks, 1986). Farid and Makarechian (1983) estimated that 60-75 percent of variation in SC (R2) could be accounted for changes in body weight during preweaning and 145-d feedlot test periods in beef bulls.…”

“…by.x = regression coefficient, r = correlation coefficient. Bourdon and Brinks (1986) reported genetic, phenotypic and enviornmental correlation coefficients of 0.77, 0.73 and 0.67, respectively, between yearling weight and POG in Hereford bulls. They also found that the corresponding relationships between yearling HHT and weaning weight were 0.61, 0.53 and 0.45, respectively.…”

“…Makarechian et al (1985) reported that linear regression coefficients of SC on PWG in yearling Herefrod, Beef Synthetic and Pee Wee breed gmups were not significantly different. On the other hand, Bourdon and Brinks (1986) reported that under more favourable postweaning test environment compared to preweaning, younger bulls that spent a greater proportion of their lives in the postweaning test, had advantage over older bulls in SC per day of age. In general, relationship between SC and growth traits were favourable (Brinks, 1994).…”

“…In general, there are positive associations between the growth parameters and scrotal circumference in young beef bulls (Makarechian et al, 1985;Pratt et al, 1991;Brinks, 1994). Growth parameters are also associated with final body weight and hip height at the end of feedlot test (Bourdon and Brinks, 1986;Schramm et aZ.) 1989;El-Barbary et al, 1995).…”