Ask the Vet

Evaluate Bulls for Breeding Soundness

Even if your bull has been getting cows bred, he should be semen-checked each year. (Jennifer Carrico)

READER: Do I need to semen-check my bull every year even though he is in good shape and seems healthy?

DR. McMILLAN: I firmly believe every bull should have a Breeding Soundness Exam (BSE) done before every breeding season. A BSE is much more than a "semen check." It is done by a veterinarian and includes a physical assessment of the bull. That assessment includes a measurement and examination of the testicles, and an evaluation of the penis and all accessory sex organs, as well as an evaluation of semen motility and morphology (normal versus abnormal shape).

I have addressed this in past columns and noted that in my career, I've identified several completely sterile bulls. Unfortunately, in one case, we identified the infertile bull after we found more than 30 open cows at the end of the breeding season. He had passed a "semen check" but was unable to extend his penis.

The more common scenario is the subfertile bull. These bulls will get some cows pregnant but not as many as a bull that has passed a BSE. How much are just two or three more calves worth at weaning? The other silent thief is that many of these calves will be born later in the calving season. This can impact weaning weights from just a few pounds to over 100 pounds in a 60-day calving season.

I also tell my clients when I "pass" a bull, it's not the end of the BSE. A bull can "go bad" at any time from disease or injury.

The second phase of the BSE falls to the producer. Watch the bull closely to make sure he can and will breed cows. Libido is not assessed in a BSE, and penile deviations also are not always noted. Lots of cows returning to heat 18 to 24 days after a heat is also a red flag that must be addressed immediately.

Putting a bull in without a BSE is like playing Russian roulette. Please don't take that chance.

READER: What timeline should I have for giving heifers prebreeding shots before artificial inseminating or turning them in with a bull?

DR. McMILLAN: I recommend at least two rounds of vaccines ideally prior to weaning. I like to use modified live virus (MLV) vaccines for infectious bovine rhinotracheitis (IBR), bovine viral diarrhea (BVD), parainfluenza type 3 (PI3) and bovine respiratory syncytial virus (BRSV) since they are less expensive than "killed" products and usually produce the highest levels of immunity. I recommend using a vaccine that also includes a five-way leptospirosis component in most cases. A seven-way clostridial vaccine is essential.

At about 12 months, I like to repeat all these vaccines, including a clostridial vaccine, but they should be given at least a month prior to artificial insemination (AI) or turning them in with a bull. MLV IBR vaccine can affect the viability of the developing egg and decrease fertility. This is not a concern with "killed" products, and there are several very effective killed products if your timeline does not allow for use of MLV vaccines. In all cases, these vaccines should include five-way leptospirosis.

In some herds, other vaccines for Mannheimia haemolytica, Pasteurella multocida and Mycoplasma bovis may be helpful in reducing these often severe respiratory diseases. Some herds will benefit from vaccination for Campylobacter fetus (vibrio). This is often combined with the IBR, BVD and PI3 BRSV vaccines, or as a stand-alone product (Vibrin).

While we are on this subject, I do not generally recommend giving clostridial boosters to adult cows in our area. Because of the timeline in getting adult cows calved out and vaccinated prior to AI or turning out the bull, I often recommend using killed vaccines in this group. If heifers have received three rounds of MLV vaccines, the best of the killed vaccines are very effective in boosting immunity.


-- Please contact your veterinarian with questions pertaining to the health of your herd. Every operation is unique, and the information in this column does not pertain to all situations. This is not intended as medical advice but is purely for informational purposes.

-- These are only my thoughts and general guidelines. Please get with your veterinarian and together develop the best program for your herd.

-- Email Dr. Ken McMillan at


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