Heritability of scrotal circumference unadjusted and adjusted in Hereford bulls

The aim of this study was to estimate the heritabilities of scrotal circumference unadjusted
(SC), adjusted for age (SCa) and adjusted for age and weight (SCaw), simultaneously, in
Hereford cattle. The data file was composed by 7,679 males, sons of 394 sires and 5,221
dams belonging to the “Conexão DeltaG” beef cattle breeding program, granted by
Gensys Ltda. The models considered as fixed the effect of contemporary group
(composed by: farm of birth, weaning and yearling, birth season, management group at
weaning and yearling, and date of weaning and yearling) and as covariates, the linear and
quadratic effects of age (AY) and weight at yearling (WY) when the scrotal circumference
was not adjusted, and the linear and quadratic effects of WY when the scrotal
circumference was adjusted for age (470 days). However, when the scrotal circumference
was adjusted for age (470 days) and weight (350 kg), only the fixed effect was considered.
The preliminary statistical analysis and adjustment factors for age and for age and weight
were estimates using GLM and regression analysis procedures (SAS/STAT 9.3, 2011).
The genetic parameters were estimates using the software WOMBAT (Meyer, 2007). The
mean and standard deviation of SC, SCa and SCaw were, respectively, 32.32 ± 3.09 cm,
32.46 ± 2.92 cm and 32.35 ± 3.05 cm. In addition, the adjustment factors for SCa ranged
from 0.9489 to 1.2108, and for SCaw ranged from 0.9986 to 1.0129. The genetic additive
variances for SC, SCa and SCaw were, respectively, 1.15, 1.22 and 1.57. The heritability
coefficients for SC, SCa and SCaw were 0.298 ± 0.043, 0.305 ± 0.043 and 0.328 ± 0.044,
respectively. Both unadjusted and adjusted scrotal circumference could respond to direct
selection. Probably the scrotal circumference adjusted by age could be better selection
criteria for growth precocity and the scrotal circumference adjusted for age and the weight
could be better selection criteria for sexual precocity. Therefore, the genetic correlation
among these traits with age at first calving in Hereford heifers must be studied.