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Well-timed updates on bull scrotal circumference

The third edition of the Bull Breeding Soundness outlines a few changes

Well-timed updates on bull scrotal circumference

The Western Canadian Association of Bovine Practitioners (WCABP) has published a third edition of the Bull Breeding Soundness manual written by Dr. Albert D. Barth, which contains some changes to the accepted minimal scrotal circumference for the different breeds at different ages. The old standard was a few years old so this new version is a well-timed update. The WCABP also puts out the standard Breeding Soundness Evaluation (BSE) forms used across Western Canada and perhaps most of Canada.

I have also seen forms from the society of theriogenology in the U.S. as well as one used in Australia and they all have some similarities.

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

These changes were made based on the compilation of thousands of scrotal circumference submissions made from veterinarians across Western Canada from 2001 to 2006 so the measurements were current, covered a large geographic area and were age and breed specific.

Most of the veterinarians would have been graduates from Western College of Veterinary Medicine (WCVM) in Saskatoon and would have been trained by the key researcher on this project, Dr. Barth. He is also the inventor of the ReliaBull scrotal tape that is the only one I am aware of which operates on a spring type mechanism so measurements between practitioners have the greatest consistency. The tape even has a plunger on it that shows red when it is time to “stop” and take the measurement. A couple of other younger researchers helped on this project including Dr. Steve Hendrick so the information from this research and subsequent recommendations were derived locally from Western Canadian purebred cattle.

In my opinion, producers have done a great job of selecting for increased scrotal size and this has been reflected in what the numbers show. You may be glad to hear there were very few changes but keep in mind the values are minimum acceptable standards based on age.

Semen production and early maturity correlate to larger testicles at an earlier age in both bulls and their female offspring.

The WCABP added a new category specifically for 15 months, as this 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 monthly intervals up to 15 months of age.

We as veterinarians and you as producers need to keep this in mind when purchasing purebred bulls. Comparing a 15-month bull to a 12-month bull evaluated on the same day may have differences in scrotal size and morphology of sperm even though they may end up being equivalent bulls when mature. Always be cognizant of birth dates when bulls are evaluated at a younger age.

Time of year also plays into this with increased riding and sexual activity in the spring. I have always said testing a May-born calf in May the next year on average will be better than doing February-born calves in February the next year simply because of the lack of activity during a cold winter and the fact cycling females are nowhere to be had that early in the year.

Other changes saw the Charolais and Angus breeds move up one cm to where the Simmental and Gelbvieh breeds were. This makes sense to those of us that semen test large groups of purebred bulls, as these breeds are all very similar in average size. The Here­ford and Shorthorn bulls also move up one cm in all their categories.

As veterinarians we know once the scrotal measurement is getting close to or on the minimum standard, this is when the majority of failures in semen quality occur.

Some breeds appear to have a bit lower scrotal size and yet mature size is up there with the other breeds. Remember: all breeds do not need the same scrotal size so for instance, we can’t compare Limousin with Gelbvieh as scrotal size will be different and Limousin will need less scrotal size than many other breeds to do the job. Watch those semen forms when purchasing bulls and remember the U.S. has a different system. With their system, scrotal sizes appear larger than with bulls done on our system. It is simply the way they measure and it can make anywhere from a two to five cm difference.

Keep the new minimum standards the WCABP have put forward in mind at the bull sales this year.

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

Purebred producers want to sell a quality, well examined, fertility-tested product. It is in their best interest to do so and even though we as veterinarians cannot identify all the problem bulls that are turned out to breeding pasture, we do go a long way toward identifying the vast majority that have or will have sperm fertility problems. A scrotal circumference evaluation is still a large part of that equation.

About the author


Roy Lewis is an Alberta-based veterinarian specializing in large-animal practice. He is also a part-time technical services vet for Merck Animal Health.



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