either the culture or the PCR test, so it takes more than 1 test,” he says. The tests need to be run a mini-
mum of twice, and preferably 3 times, at least a week apart to know if the bull is actually negative be- fore he is put with cows. With 3 negative tests, a person can be 99
know that 1 test is not always suf- fi cient. The number of organisms a bull may have in his sheath goes up and down. If you can do multiple tests and they are all negative, you have much more confi dence that the bull is indeed negative,” says Hairgrove.
not been tested, or you don’t know if he’s been tested, I would recom- mend having him tested before he’s brought into the herd,” says Gill. Having a bull turn up BVD-PI
is not common, but it can happen. “BVD is easy to test for, and if your veterinarian is going through a bat-
BVD is easy to test for.
percent sure the bull does not have trich. “Very few ranchers are doing multiple tests, however, so now we are fi nding more and more bulls introducing trich to the cow herds they are coming into,” Gill says. “You should always test a new
bull for trich, but you also need to know the history of that bull,” says Hairgrove. “We’re currently work- ing on a research project, bringing some infected bulls to the college to study — to look at some of the vari- ables when testing bulls for trich. “One test is not always suffi cient
to know if the bull is actually nega- tive. Is the bull harboring a suffi - cient number of organisms to detect at that point in time? Was shipment of the sample to the lab delayed or subjected to temperature extremes that may invalidate the sample? The tests do not always pick up every positive bull,” he says. If there are insuffi cient numbers
of organisms in the sample or some contamination, even the most so- phisticated molecular diagnostics (PCR test) will not pick up the infec- tion. Careful handling of samples and meticulous attention to detail enhance chances for a good test. “It’s amazing how the infect-
ed bulls will vary from week to week. We are not fi nished yet with our study project, but we’ve done enough testing around the state to
100 The Cattleman October 2013 “If a producer tests a purchased
bull and the bull tests positive, that bull is defi nitely infected. But if the bull tests negative, that’s no guaran- tee that he’s actually negative. Bulls entering semen collecting stations are required to have 6 negative tests before collection,” says Hairgrove. “So should we test a bull again
if his fi rst test was negative? What level of risk is a producer willing to accept? If the producer does not know the bull’s background, I rec- ommend doing more than 1 test. It is an expensive test, but not nearly as expensive as dealing with trich in your herd.” Vibrio is another concern. “Of-
ten bulls have not been vaccinated for vibrio, particularly if they are virgin bulls,” says Gill. It is possible to bring any sexually transmitted disease into your herd, even when purchasing bulls assumed to be virgins.
BVD Some of the viral respiratory/
reproductive diseases like IBR and BVD can be brought into a herd by an infected bull. “It’s important to see whether a bull is persistently infected (PI) with BVD. We’ve seen some bulls come into a producer’s herd that looked good and showed no signs of BVD, but then found out they were carriers. If the bull has
tery of tests for the bulls this is something you should add. This can be done with an ear notch, but we’ve also found some bulls that carry the BVD virus in their se- men,” he says. Hairgrove says a person needs to
make sure that a new bull is not per- sistently infected, but should also check the bull’s vaccination history. “If a bull is exposed to the BVD virus before puberty (with certain live-virus vaccines), the virus can replicate in the testicles and the bull will shed virus in his semen, some- times for an extremely long time. There have been instances in which producers used a modifi ed-live non- cytopathic vaccine in young bulls (pre-puberty), producing prolonged testicular infection,” he says. “The testicles are somewhat iso-
lated from the rest of the body and the immune system, and this helps prevent a bull from developing a reaction to his own sperm cells. But this also makes it to where if a bull is infected with BVD prior to puberty and the virus gets into the testicles, once he reaches puberty the virus doesn’t get back into the general circulation and is therefore not exposed to the immune system. He won’t sero-convert or test posi- tive, but when he breeds a cow he could pass the virus to her. “This infection in the testicles
thecattlemanmagazine.com
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