Relationships of Sire Scrotal Circumference to Offspring Reproduction and Growth

Abstract

Reproductive and growth data were obtained on 779 and 564 yearling beef heifers and bulls, respectively, that had sires with yearling scrotal circumference data at the San Juan Basin Research Center, Hesperus, CO. Partial regression coefficients of reproductive and growth traits on inbreeding (FXC) and age of the individual and adjusted scrotal circumference of sire (SCSI) were obtained. Growth and reproductive traits of heifers and growth and breeding soundness traits of bulls were analyzed. Separate analyses for each sex were performed, but least squares models were similar. Models included fixed effects of breed, birth year (BY), age of dam (AOD) and the covariates FXC, age (day of birth in heifer analyses) and SCSI. Scrotal circumference of sire was adjusted for age, FXC, AOD and BY using values obtained in a separate analysis. Seminal traits improved as age increased, and there was a seasonal effect present for age of puberty. Inbreeding had a detrimental effect on reproductive traits. Partial regression coefficients for the reproductive traits on SCSI were: age of puberty, -.796 d/cm; age of first calving, -.826 d/cm; julian day of first calving, -.667 d/cm; julian day of second calving, .597 d/cm; most probable producing ability, .132 %/cm; percent sperm motility, -.74 %/cm; percent primary sperm abnormalities, .08 %/cm; percent secondary sperm abnormalities, .92 %/cm; percent normal sperm, -1.28 %/cm; total breeding soundness examination score, .28 units/cm and scrotal circumference, .306 cm/cm. A heritability of .39 was obtained for scrotal circumference.

Genetic relationships between scrotal circumference and female reproductive traits1

“…Similar estimates were found by Smith et al (1989) for a population that included Hereford and Angus cattle and by Morris et al (1993) for an Angus population (0.10 ± 0.17 and 0.15 ± 0.09, respectively). In contrast, several studies have reported higher estimates of heritability (from 0.27 ± 0.04 to 0.61 ± 0.17) for AP (e.g., MacNeil et al, 1984;Gregory et al, 1995;Morris et al, 2000).…”

“…Similar estimates of heritability (0.01 ± 0.12 and 0.07 ± 0.09) were reported by Bourdon and Brinks (1982) and Smith et al (1989), respectively. Several authors, however, have found higher estimates of direct heritability for AFC.…”

“…In agreement with those results, Moser et al (1996) concluded that Limousin bulls with high yearling SC EPD could be expected to produce daughters reaching puberty at significantly earlier ages. In contrast, Smith et al (1989) and Perry et al (1990) reported nonsignificant relationships (P > 0.05) between age at puberty in heifers and SC of yearling males.…”

“…Scrotal circumference is easy and inexpensive to measure, has moderate heritability, and is reported to be favorably associated with female fertility (Brinks et al, 1978;Morris et al, 1992;Vargas et al, 1998). Positive genetic correlations between SC and growth traits (Bourdon and Brinks, 1986;Smith et al, 1989;Keeton et al, 1996) and between SC and semen quality traits (Neely et al, 1982;Knights et al, 1984;Smith et al, 1989) have been reported.…”

Genetic relationship between growth and reproductive traits in Nellore cattle

“…Thus, 9500 samples were effectively used to estimate the parameters and highest posterior density (HPD) intervals. The Bayesian Output Analysis package (Smith, 2005) was used to calculate the mean, mode, median, s.d. and 95% HPD interval.…”