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Assessing risks for venereal disease in cattle

There are several sexually transmitted diseases in cattle that can be costly if they sneak into your herd, resulting in reproductive losses, says Dr. Cheryl Waldner, professor of epidemiology at the Western College of Veterinary Medicine in Saskatoon. “Diseases we’ve seen in the last few years that are having an important impact on reproductive performance — and the ones producers should never forget — are BVD and IBR. The other two are trichomoniasis and vibrio, which can present a serious problem, depending on how ranchers manage their animals,” she says. Vibrio is also known as bovine genital campylobacteriosis. If your cattle come into contact with other herds this will increase the risk.

Cattle grazed on community pastures, or that have fenceline contact with neighbours’ cattle may be at risk. Even people who have a closed herd may occasionally have a neighbour’s bull come through the fence, or a cow go visiting. All it takes is a broken fence to end up with a problem.

“For trich and vibrio there must be direct sexual contact. BVD is more communicable and can be passed across fencelines with nose-to-nose contact, or via common water sources as well as through sexual contact. If you buy an infected bull he may spread BVD to your cows in several ways,” says Waldner.

“The good news for BVD is that there’s a fairly good vaccine. One of the things we’ve learned from data analysis is that we can see a difference with vaccination, especially on community pastures. We have direct evidence that it does pay to vaccinate for BVD and IBR,” she says.

“There is a difference in pregnancy rates in community pastures for cows that are vaccinated compared to ones that are not. The vaccine gives sufficient protection, so their pregnancy rates should be the same as the cows kept at home. If their vaccines are up to date there shouldn’t be any problem. The only cows that showed up with lower pregnancy rates were the ones that were not vaccinated,” Waldner says.

Dr. Cheryl Waldner

Dr. Cheryl Waldner

“Some diseases are very frustrating because there is not always an easy fix, but with BVD vaccination does help. The picture becomes more clouded when dealing with trich and vibrio. We don’t have a good vaccine for trich. We do have vaccine products for vibrio but we don’t know as much about how well they work; they haven’t been studied as much as the BVD vaccines. Even though we don’t know as much about them, I would recommend the use of vibrio vaccines if a person is using community pastures. It will provide some insurance,” she says.

Biosecurity and testing

“We have good tests for trich. If there is any suspicion that there is risk for exposure, you need three tests — even with the newer PCR tests — to make sure a bull is not carrying this disease. The PCR test can be more sensitive than the old culture tests but still not perfect. It might not pick up a positive bull because an infected bull might not be shedding large numbers of organisms at the time of the test. The level of trich shed by the bull can fluctuate.” You have more chance of finding the organism if you test more than once.

“You need three tests before you can safely call a bull negative for trich. Every additional negative test gives you more confidence. You know a lot more about a bull by testing once than if you don’t test at all, and you know even more if you test twice. But to be sure the bull is negative, particularly from a herd with a history of reproductive problems, it’s best to test three times,” she explains.

“The same applies to the new vibrio tests. To be absolutely sure that a bull is negative, we suggest having three tests,” Waldner says.

Both the trich and the vibrio tests are done in the same manner, taking samples of material inside the bull’s sheath. “The veterinarian uses an AI pipette attached to a syringe and takes a certain amount of sample. Depending on where the sample is going (which lab), there are different options. Most of the trich tests are still done using incubation pouches for shipping the samples (the pouches we used to use when we were doing cultures) but we can also put the sample into phosphate-buffered saline — a special salt solution. The nice thing about that method is that it is cheaper, which helps when you are doing a large group of bulls,” she explains.

“The good thing about collecting samples into the PBS solution is that you can collect a single sample and test for both organisms (trich and vibrio). This saves money because you only have to collect one sample, it goes into the cheaper phosphate-buffered saline and you don’t have to keep the samples warm like we did with the old culture pouches. With the old cultures there could be problems if you tested early in the year and the sample froze on the way to the lab. With the new tests you can just put the samples on ice packs to keep cool and can send them any time of year and they will be fine,” says Waldner.

“The only caution with vibrio testing is that the amount of organism the bull is shedding seems to fluctuate. Testing bulls in really cold weather doesn’t seem to be as effective or accurate as testing them when weather is warmer. The test for trich is not as fussy; those organisms do not seem as sensitive to cold. We have noticed that the vibrio test is less sensitive in cold weather, especially as temperatures drop below 0 C. When the temperature is 5 C or warmer the test is more accurate,” she explains.

“If you decide to test just once for vibrio, make sure the weather is warm. If you are testing only once and it’s -20 C, there’s a good chance you could miss this organism. We have found positives when it’s cold, but you are less likely to find all the positive bulls in cold weather. If you have a bull you want to keep over for next year, you should either check him in the early fall before it gets cold, or be prepared to wait until spring when it warms up,” she says.

Pooled samples

If you have 15 bulls, for example, you would collect the 15 samples and the veterinarian would send those samples to the lab, but you can request that they be pooled. “The evidence we have right now suggests that we could probably group them in larger batches, but pools of five can still save significant expense. If the test comes back negative you are OK, but if it’s positive you’d have to go back and check each one again individually. This is why you don’t want your pool size too large, or it becomes more expensive having to do those bulls all over again to find out which one(s) were positive,” explains Waldner.

Pooling samples can be beneficial, however, if you need your bulls tested before they go to community pasture and you don’t have any reason to believe your herd is currently infected (pregnancy rate is high). It can also be beneficial if you have large numbers of bulls to do, saving money on the individual testing if there’s a likelihood that you won’t have to go back and recheck very many of them.

Best to test

Some grazing associations are requiring tests for trich, and request that the cows be vaccinated against BVD or have a calf at foot (evidence they didn’t abort from reproductive disease). “I don’t know if any grazing leases require vibrio vaccination of cows, but some may strongly recommend it,” says Waldner.

“We have to realize that whether it’s vibrio, IBR or BVD, no vaccine is perfect; not all cows mount adequate immunity. It’s safest to use a combination of approaches and not rely entirely on vaccine. If you have a high-risk situation you should consider vaccinating and also do your best to make sure that bulls going into the herd are clean and not carrying diseases. They can be tested for BVD with ear notch samples. This test is inexpensive and can be beneficial when bringing in new bulls — to make sure none have BVD. If you are bringing in virgin yearling bulls the chances that they would be positive for trich or vibrio are very low, but they could be carrying BVD. These are the bulls that should definitely have the BVD test.”

It may seem like a costly inconvenience to test bulls, but it may save a much greater cost by preventing reproductive losses. “Trich and vibrio are devastating. Some of the pregnancy rates that we’ve seen in affected herds (a 30 to 50 per cent calf crop) can wipe out a producer. There are very few ranchers who can deal with one year of that kind of loss, let alone several.”

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