Subfertile bulls negatively influence the cow herd and the producer’s income. Occasionally, producers hire veterinarians to pass subfertile bulls after being failed by a previous veterinarian. Learn why experts discourage this practice.

Freelance Writer
Gilda V. Bryant is a freelance writer based in Texas.

Erika L. Lundy, beef specialist at Iowa State University, says second to feed cost, reproductive success has a substantial economic impact. If a bull fails the BSE, reproduction slides in the cow herd, causing a loss of income.

Cows may not breed as early, leaving the producer with late calves that are lighter at weaning, earning less when sold. Poor bull performance extends the breeding season, and open cows might be culled unnecessarily. Different ages and weights of calves are more difficult to market and manage due to an uncontrolled breeding season. While most seedstock producers sell their best performing bulls, those who don’t risk their reputations and future sales.

Veterinarians should check bulls 45 to 60 days before turnout. If a bull fails the BSE, the producer has time to buy another animal. Lundy recommends avoiding BSEs in February or March in colder climates because bulls might experience frostbite that could lower fertility.

“It’s not uncommon for 25 percent of yearling bulls to fail the BSE,” Lundy reveals. “We can do everything right with that animal in the developing process; however, one out of five bulls fail the BSE. The BSE ensures we have good breeders.”


Lee Jones, DVM at the University of Georgia College of Veterinary Medicine, says his job is to find bad bulls. When he prevents a significant failure, his clients benefit. Bulls passing the BSE breed more cows and produce 50 pounds more calf per cow when cows are bred during the first service. This adds value to the operation.

“I help farmers prevent reproduction disease and develop good nutrition and health programs to ensure their cows are ready to be bred,” Jones reports. “If they use a bull that isn’t capable, it’s not the cow’s fault. One infertile cow only affects her. One infertile bull can affect 20 to 30 cows, breeding late or not getting bred at all.”

It is a misconception that bulls passing the BSE are guaranteed breeders. They may fail to breed cows due to an internal nerve malfunction, poor social adaptability or lack of libido. When Jones investigates herd fertility problems, he tests bulls first to confirm or eliminate them as a possibility. This logical approach saves the producer time and money.

“One bull should be able to service 25 cows,” Jones shares. “In this case, the BSE is a two-dollar-and-50-cent per-cow investment. Operators spend more on vaccinations for cows than they would a BSE. When you look at a per-cow basis, BSEs are very cheap.

“Have a BSE performed on a yearling bull and every year after that because bulls go bad,” Jones advises. “Seedstock producers need to know they’re selling fertile bulls. Commercial operators should ask the seller if a prospective bull had a BSE performed by someone trained to execute a complete BSE outlined by the Society for Theriogenology (Theriogenology). Their guidelines establish the best standard for BSEs. We don’t fail the bull; the bull fails the test.”

Chance Armstrong, DVM, Louisiana State University Veterinary Clinical Sciences, states that emotions can often ride high when a bull fails to pass a BSE. Most owners have a lot invested in their bulls; it is always difficult to hear they must spend more money to replace one. When a veterinarian diagnoses a bull as an unsatisfactory potential breeder, it is with the owner’s best economic interest in mind.

The BSE is designed to find bulls that can effectively and efficiently breed 25 or more females in a 60- to 70-day breeding season. Based on test results, a bull receives one of three classifications:

  • Satisfactory potential breeder (fertile)
  • Unsatisfactory potential breeder (subfertile or sterile)
  • Deferred (postponed for further testing)

“The bull plays an important role in the profitability of cow-calf and seedstock operations,” Armstrong argues. “You have to know how he is performing prior to each breeding season. A BSE is the cheapest insurance policy producers can purchase.”

During BSEs, the veterinarian examines the animal’s physical condition. He checks vision, hoof and leg health, looking for lameness, deformities or conformation issues that interfere with a bull locating cows in heat and completing the breeding act. The veterinarian also evaluates testicles and scrotal circumference for normal health and size.

“There’s an inverse relationship between the increased scrotal circumference and when the heifers he sires reach puberty and come into estrus,” Armstrong notes. “Coming earlier into production brings a return to the operation sooner compared to heifers sired from bulls with a smaller scrotal circumference.”

The BSE assesses semen quality by checking sperm motility and morphology. There must be a minimum of 30% progressively motile sperm and 70% morphologically normal sperm cells to pass this section of the exam.

“Studies indicate that abnormal sperm morphology has been the most common reason bulls were classified in the unsatisfactory or deferred categories,” Armstrong warns. “If you’re not assessing sperm morphology, you’re missing something because most bulls don’t fail on the motility assessment alone. Usually, if he fails the motility assessment, he fails the morphology assessment. You’re doing yourself and the industry a disservice if you look under the microscope, see something moving and call that a satisfactory bull. That’s not good enough. That’s below the expectations of what every producer should expect.”

Armstrong recommends bulls have a body condition score (BCS) of 6 to 7 because they will drop two BCSs during breeding. They should be athletic but not overconditioned, which can lead to joint problems. Make sure he has energy reserves he can draw on to generate quality sperm.

Yearling bulls are the most commonly deferred group. Producers can repeat the BSE in 60 days. Those that are peripubertal will likely pass with more time to mature. Subfertile bulls or those with heritable defects should be marketed for beef.

“Nutrition is critical for developing young bulls,” Armstrong advocates. “Having a great relationship with your veterinarian is important to provide preventative care. The period from birth to weaning is nutritionally critical for setting up potential herd sires for success. The testicles are developing during that time and can be heavily influenced by nutrition. Young bulls require more protein on a dry matter basis than older bulls. A moderate rate of gain keeps them from being overconditioned. Tailor your nutritional development for bulls to gain 2 pounds a day with a target of 75 percent of their mature weight by 2 years old. Carrying fat has a negative impact on joints and long-term health. We want to prepare them to spend many years in the cow herd, not marketed for beef prematurely because of lameness issues.”

The BSE is a core procedure that should be performed on every bull. It is not perfect; it is a snapshot in time. It is simply the best way to ensure that bulls reach their full breeding potential every year.

And that’s no bull. end mark

PHOTO: Emotions can run high when a bull doesn’t pass a breeding soundness exam, but it is always with the owner’s best economic interest in mind. Photo by David Cooper.

Gilda V. Bryant is a freelancer based in Amarillo, Texas.