How to ‘insure’ your bull this breeding season

Farm Forum

One of the most important insurance policies a cow-calf producer can have is not underwritten by State Farm or De Smet Farm Mutual. It’s available through a veterinarian. I have “written” many of these policies over the years and saw firsthand how many times producers have “cashed in” on them.

The policy I’m talking about is a bull breeding soundness examination (BSE). I can’t overestimate the importance of bull fertility to the productivity of a cow herd. For bull-bred herds, it’s beyond critical. It’s almost comparable to the importance of rain to crop farmers. But in the case of dry cornfields, there’s usually at least something to chop for silage. If bulls aren’t able to successfully breed cows, there is no crop – period.

Granted, it’s rare for a bull to be completely sterile. A good BSE will identify bulls that are sub-fertile as well. Sub-fertile bulls are drains on the cow-calf enterprise, too. The investments in bulls by today’s producers are as high as ever, so each animal needs to back that up by efficiently breeding their fair share of cows.

Each bull needs this insurance policy because we can’t pick out infertile or sub-fertile bulls just by looking at them. Moreover, it’s dangerous to “roll the dice” and assume a bull is good. Studies show that we can expect 15% of bulls to be “unsatisfactory” breeders in any given year.

A proper BSE requires three components – two of which involve direct examination of a semen sample.

First off, the veterinarian measures the bull’s scrotal circumference. This directly measures the bull’s serving capacity – how many cows he is able to handle. On the BSE scoresheet, this is a “pass-fail” test. The bull has to exceed a minimum circumference — 30 centimeters for a young bull up to 34 centimeters for two-year-olds and up. These are rock-bottom minimums; most bulls will measure much larger. A recent report from Canada showed that average bull scrotal circumference has increased over the years. Thus, we may see new minimums established in the future.

Next, a semen sample is examined under the microscope. The veterinarian will judge the sample’s motility – how well the sperm cells move individually and as a group. The pass-fail threshold here is 30% motile sperm in the sample.

The next part of the BSE is important – assessing the morphology of the sperm cells. The individual cells are stained and examined for abnormalities under the microscope. To pass, a bull needs at least 70% normal sperm cells. Hot conditions, stresses due to injury or illness, or bull immaturity can cause defective sperm cells that won’t be able to fertilize an egg. Morphology analysis is technically difficult so it is sometimes skipped by lay examiners. Not examining morphology during a BSE is unfortunate and unacceptable: poor morphology is the reason for as many as 50% of BSE bull failures.

A good BSE will also include a thorough evaluation of the whole animal: the feet, legs, eyes, and internal and external reproductive organs.

The best time for a BSE is not too early (what if something changes between the test and breeding cows?) and not too late (where can one find a replacement bull if one “flunks”?). Veterinarians will sometimes classify a bull as “decision deferred”, meaning that the bull doesn’t pass today, but may pass later, given time. This extends the testing period for these bulls. Yearling bulls often fall into this category. Studies show that only about 35% of 12-month-old bulls produce BSE-satisfactory semen. Most of these bulls will improve over time. This improvement is not assured though, so a full retest is necessary at least 3 to 4 weeks later.

And it’s worth remembering that the BSE only measures the bull on the day he’s tested. It doesn’t assure that a passing-grade bull won’t encounter problems like injuries or pinkeye after he’s turned out to pasture. Producers should build in time to observe bulls once they’re on the job, and quickly respond to problems when identified.

Cow-calf herds simply have too much at stake to not test every bull that goes out to pasture. Breeding soundness exams involve extra effort and cost, but they are insurance policies one shouldn’t live without.

Russ Daly, DVM, is the Extension Veterinarian at South Dakota State University. He can be reached via e-mail at or at 605-688-5171.