Odonnell tyler
Associate Extension Educator / University of Idaho Extension

As temperatures start to warm here across the West, calves are hitting the ground, and producers are getting their first look at how their mating choices are paying off and are likely starting to get ready for the next breeding season. Obviously, we want to pair cows with the bull that is going to make the best progeny for our operation's goals, but how do you know if that bull will perform? I am sure we all wish we had a crystal ball that could tell us, but we must use the tools that we have available, and that starts with a breeding soundness exam.

Breeding soundness exams give us an idea of a bull’s conformation, their scrotal circumference as well as their sperm motility and morphology. These three indicators predict the bull’s ability to perform in the pasture. There are three categories of breeding soundness scores: pass, fail or defer, the latter referring to a bull that did not pass the first exam; however, they have the potential to pass later in life or after recovering from an injury or other environmental factor.

The first step in a breeding soundness exam is the overall conformation of the animal and determining if they are physically able to breed. Factors such as structure, condition, soundness and external signs of disease all play into this evaluation. Injury in bulls throughout the breeding season can be a concern and should be monitored.

Once we are satisfied that our bull’s external appearance is appropriate to put on the pasture, a scrotal circumference measurement should be taken. This is traditionally performed by a veterinarian when they do a breeding soundness exam but is a relatively simple measurement to be taken with a scrotal tape. Using the tape, find the widest portion of the scrotum, and wrap the tape around and measure where the notch or bar runs across the tape. This measurement is in centimeters and correlates with a bull’s age. A bull should be 30 centimeters at 15 months old or less, 31 centimeters at 15 to 18 months old, 32 centimeters for 18 to 21 months, 33 centimeters for 21 to 24 months, and all bulls over 24 months should have at least 34 centimeters. This is one way a bull can be deferred; if they do not meet the scrotal circumference the first time, they can be remeasured at a later date.


The last part of the breeding soundness exam is sperm motility and morphology, which is performed by your veterinarian. They will look for the percentage of live sperm that are physically normal under a microscope. It is important to remember that environmental factors have a large effect on sperm, and changes to the environment can affect both sperm production and morphology throughout the breeding season.