Ask The Vet

Dr. Ken McMillan, Contributing Columnist

Q: We live on flatlands with lots of trees, brush and swampy areas in Manitoba. Is there any research that shows whether it’s preferable to keep one bull with 30 cows per pasture, or have six bulls in with the 180-head cow herd.

A: This is a great question. I know of no research that specifically looks at the economics of these two different approaches. There are advantages to a multisire breeding program. First in my mind is the fact that any bull can “go bad” at any time. This may not be obvious when it happens, and he may still be breeding cows. Additionally, if several cows come into heat at one time, multiple bulls should be more effective at servicing and settling them. There is also less need for fencing and working facilities with the multisire approach. Larger pastures can be used, or you can rotate through several pastures as forage availability dictates. The multisire program is one of my favorite management practices.

Like every good thing, there are some possible drawbacks to consider, too. High on the list, injury to bulls and even cows, increases when there are multiple bulls in the herd. You also don’t know the sire of a calf without DNA testing. And, if the “boss” bull is infertile, he may beat back fertile bulls, preventing cows from getting pregnant.

I found one study that looked at multisire breeding programs in several large herds. Those researchers found, on average, bulls sired 15 to 20 calves per breeding season. However, some bulls sired more than 50 calves. And, 7.3% of bulls in the program sired no calves. In at least half of the breeding seasons, at least one bull was removed due to injury or poor condition.

All of this tells me that highly prolific bulls will have a disproportional impact on genetic trends in the herd. Are these bulls the genetically superior bulls? Do we want those prolific bulls to determine the direction of the herd? I would encourage readers to write or email if they have thoughts on this issue.

Q: Do you have a suggested program to make sure bulls are ready for breeding season?

A: Several months before your turnout date, you need to decide if any bulls should be replaced. Then consider whether you have enough bull power to get through the breeding season. Remember, your bulls contribute 50% of the genetics to each calf crop, so having enough quality bulls to do the job is extremely important. Never be in a last-minute rush to find a bull.

If you need to add a bull or bulls to the herd, virgin bulls help avoid introducing diseases. But, all new bulls should be quarantined three to four weeks. Ideally, nonvirgin bulls should be tested for vibrio, leptospirosis and trichomonas. This is especially important for bulls purchased from a sale barn or those with an unknown history.

I recommend having your veterinarian do a complete Breeding Soundness Exam (BSE) on every bull 30 to 60 days prior to breeding season. This gives you time to find additional bulls if there’s a problem. A BSE must include a physical exam to make sure the bull is sound and able to breed. Each bull must meet minimum requirements with regard to scrotal circumference, motility and normal sperm to be classified as a “satisfactory potential breeder.”

Bulls should also be vaccinated at this time if due. Your herd veterinarian is the best person to decide the preferred program, but, in my mind, core vaccinations should include IBR (infectious bovine rhinotracheitis), BVD (bovine viral diarrhea), PI3 (parainfluenza virus 3), BRSV (bovine respiratory syncytial virus) and leptospirosis. Other vaccines including vibrio (Campylobacter) and trichomonas may be needed in some herds. Most bulls should also be treated for internal and external parasites prior to breeding season.

I know this sounds like a lot, but the cost of a completely sterile bull (and I have found several in 37 years) can exceed $30,000 in losses. Even a subfertile bull can cost you thousands in lost conceptions. So, a BSE and a current health-care program are a small price to pay to make sure you’re getting full use of your resources.

Lastly, remember body condition is important on bulls. At turnout, I recommend they be at a body condition score (BCS) of around 6. Bulls that are too fat, especially if on full feed, “melt” when turned out with cows. Feeding a quality mineral year-round is essential in keeping bulls at their best.

If bulls are to be used in multisire groups, they should be introduced to each other prior to turnout. I’ve found this can help minimize fighting and injuries when they should be breeding cows.

Please contact your veterinarian for 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.

Write Dr. Ken McMillan at Ask The Vet, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email vet@progressivefarmer.com.

[PF_1218]

Copyright 2019 DTN/The Progressive Farmer. All rights reserved.