Scrotal circumference for yearling bulls is collected between 320 and 440 days of age. Scrotal circumference is measured using a scrotal tape around the widest part of the scrotum when the testicles are fully extended. The tape should be pulled firmly around the scrotum. It is recommended to record the measure a few times to ensure accurate results. The circumference of the scrotum is recorded in centimeters.
The Beef Improvement Federation recommends age adjustment factors specific to breed for bulls less than 12 months old. The recommendations are presented in the table below. The age adjustment factor should be used in the following equation:
365-day Srotal Circumference = actual Scrotal Circumference + [(365 - age in days) x breed specific age adjustment factor]
|Age Adjustment Factors for Scrotal Circumference|
Most breed associations record scrotal circumference and therefore have developed their own age adjustment factors for scrotal circumference. Certain associations also have an age of dam adjustment factor for yearling scrotal circumference. It is recommended to use the breed association adjustments when possible in order to increase the accuracy of the adjusted measure.
Scrotal circumference is generally measured with other yearling bull measurements including weight and height, so use of the same contemporary grouping strategies as those for yearling bulls would apply.
Scrotal circumference should be run in a multiple-trait model with a regularly recorded trait such as yearling weight.
Scrotal circumference is measured due to its positive relationship with the potential number of sperm cells that the bull can produce. It has been shown bulls with larger scrotal circumference reached puberty and produced higher quality sperm at a younger age and that their daughters also reached puberty at a younger age. Furthermore, larger scrotal circumference has been associated with an increased percentage of progressively motile sperm and less abnormal sperm production .
Yearling bulls offered for sale would usually have a Breeding Soundness Exam that would include scrotal circumference. Scrotal circumference can provide a more accurate predictor of onset of puberty when compared to other measurements such as height or weight. Due to the relationship between scrotal circumference and measures of reproductive performance, producers may wish to utilize scrotal circumference as a culling factor and place selection emphasis on scrotal circumference EPD.
- Geske, J. M., R. R. Schalles, and K. O. Zoellner. 1995. Yearling scrotal circumference prediction equation and age adjustment factors for various breeds of beef bulls. Ag. Exp. Sta., Kansas State Univ. Rep. of Progress 727:99.
- Christmas R. A., D.W. Moser, M.F. Spire, J.M. Sargeant, and S.K. Tucker. Genetic relationships among breeding soundness traits in yearling bulls. In: Cattlemen’s Day. 2001. Manhattan, KS. Pp. 1-3.
- Garmyn, A.J., D. W. Moser, R.A Christmas, J.M. Bormann. 2011. Estimate of genetic parameters and effects of cytoplasmic line on scrotal circumference and semen quality traits in Angus bulls. J. Anim. Sci. 89: 693-698.
- Carson, R.L. and J.G. Wenzel. 1997. Observations using the new bull-breeding soundness evaluation forms in adult and young bulls. Vet Clinics of North America: Food Animal Practice. 13:305-311.