Higher minimum acceptable scrotal size based on age, breed

The Western Canadian Association of Bovine Practitioners has slightly changed the accepted minimal scrotal circumference for different breeds at different ages. 


The association also publishes the standard breeding soundness exam forms used in Western Canada and perhaps most of Canada. I have also seen forms from the Society for 
Theriogenology in the United States, as well as one used in Australia. They all have similarities. 


I would say average scrotal circumference for all breeds has increased since the standard was last updated in 2000, and it makes sense to try and select for it because scrotal circumference is moderately to highly heritable. 


These changes were based on the compilation of thousands of scrotal circumference submissions made from veterinarians in Western Canada from 2001-06, so the measurements were current, covered a large geographic area and were age and breed specific. 


Most of the veterinarians would have graduated from the Western College of Veterinary Medicine in Saskatoon and trained by Dr. Albert Barth, the key researcher in the project.


Barth is also the inventor of the Reliabull Scrotal Tape, which is the only one I am aware of that operates on a spring type mechanism for greater consistency between practitioners. 


The tape even has a plunger on it, which shows red when it is time to stop and take the measurement. 


Other younger researchers also helped on the project, including Dr. Steve Hendrick, so the research information and subsequent recommendations were derived locally from western Canadian purebred cattle. 


Producers have done a great job selecting for increased scrotal size, which is reflected in what the numbers showed. 


Few changes were made, but the values are minimum acceptable standards based on age. The WCABP put in a new category specifically for 15 months because it is generally the end of the rapid growth spurt in testicle size. 


Veterinarians generally would not start testing until a bull calf is at least a full year of age, which is why minimum requirements are shown for each breed in month intervals up to 15 months of age. 


Veterinarians and producers need to keep this in mind when buying purebred bulls. 


A 15-month bull and a 12-month bull that are evaluated on the same day may have differences in scrotal size and morphology of sperm, even though they may end up being equivalent bulls in the end.


Producers should always be cognizant of birth dates when bulls are evaluated at a younger age. The time of year also plays into this with increased riding and sexual activity in the spring. 


Doing a May born calf in May the next year will usually be better than doing February born calves in February the next year, simply because of the lack of activity in a cold winter and a shortage of cycling females. 


Other changes saw the Charolais and Angus breeds move up one centimetre to where the Simmental and Gelbvieh breeds were. 


This makes sense to those of us who semen test large groups of purebred bulls because these breeds are all similar in average size. Veterinarians know that most failures in semen quality occur once the measurement gets close to or on the minimum standard. 


Hereford and Shorthorn bulls also move up one cm in all their categories. 


Some breeds appear to have a smaller lower scrotal size and yet their mature size is up there with the other breeds. 


All breeds do not need the same scrotal size, which means we can’t compare Limousin with Gelbvieh because scrotal size will be different, and Limousin will need less scrotal size than other breeds to do the job.


Watch the semen forms when buying bulls, and remember that the U.S. has a different system. As well, keep the WCABP’s minimum standards in mind. 


I commend the association for taking this approach to improving the quality of all cattle breeds, and I am sure purebred producers do as well. 


Roy Lewis works part-time as a technical services veterinarian with Merck Animal Health in Alberta.