Determining the Soundness of a Breeding Bull

Wednesday, March 4, 2020

If you're in the market for a bull this spring, you've got a lot to think about. There are many production considerations including calving ease, calf growth potential and the improving genetic traits in the herd. You want to get the most for your money on this big investment.

As a veterinarian, I'm also concerned about some other major bull characteristics: reproductive soundness, musculoskeletal soundness and the potential to introduce disease into the herd. Reproductive and musculoskeletal soundness help ensure that he can do his job long-term. Screening a bull for diseases that can negatively impact the herd helps ensure you don’t pay good money to bring in a problem.

A breeding satisfactoriness evaluation (BSE) should be performed by a veterinarian on any bull sold. Never accept delivery of a bull that does not have a signed breeding soundness examination form from a veterinarian. A thorough evaluation consists of a physical exam, a reproductive exam and semen evaluation for sperm motility/morphology. It may also include disease testing. You should also have another complete evaluation of the bull performed by your veterinarian upon receipt.

A complete physical examination should be performed on every bull. Bulls may pass the reproductive exam but not be physically able to breed the cows, compromising your calf crop. Any injury or structural deformity to the limbs, joints, or feet could impair breeding ability.

Energy expenditure of bulls during breeding season is very significant, and bulls should be in good body condition before being turned out with the cows. Both thin and overfat bulls may experience physical challenges over the course of the breeding season. It is unfortunately common for young bulls that have been aggressively developed on feed be overfat at sale time. These bulls will often fall apart when turned out on cows. Bulls pushed on feed in this way are also at greater risk of developmental joint diseases that can lead to significant lameness and a shortened productive life.

The target body condition score for bulls is 5-6/9. Bulls also need to be able to see well in order to detect females in heat. The bull’s eyes should be examined for the presence of scars from any previous pinkeye episodes or trauma.

A thorough reproductive examination should also be performed on each bull. Abnormalities such as enlargement, infection, and degeneration of any of the structures of the reproductive tract can decrease a bull’s fertility.

Once a sample has been acquired, the semen is evaluated for motility and morphology in an important part of the exam.

Morphology refers to the shape and structure of the sperm cells. Greater than 70 percent normal sperm are needed to pass a bull. Morphology is especially important to evaluate in young bulls; an abnormal morphology has serious impact on fertility. At the time of the morphology exam, signs of infection can also be recognized through the presence of white blood cells.

A variety of structural changes can inhibit the ability of sperm to fertilize the egg and, even though the sperm are alive and swimming on the motility exam, they must have structural integrity to perform their job. A common morphologic defect seen in sperm cells is the proximal droplet, seen in Figure 1 at the junction of the head and tail. This is the most common abnormality we see in young bulls. Sperm cells with proximal droplets do not bind properly to eggs and have reduced fertilization capacity.

While breeding satisfactoriness evaluations are not a guarantee of a bull’s breeding ability, they provide a vital snapshot of the physical state and semen quality of a bull at the time of the test. The economic impact of one bad bull makes these exams one of the best forms of reproductive insurance for the herd.

STORY BY: Meredyth Jones, DVM, MS, DACVIM, an associate professor in food animal medicine and surgery at the Oklahoma State University College of Veterinary Medicine. She is a diplomate of the American College of Veterinary Internal Medicine (Large Animal).