health depends on many things, including a good nutrition program, vaccination, and minimizing the possibilities for new diseases to enter the herd. One of the most common ways in which diseases come into a herd is with new animals, and these animals are often new bulls. Biosecurity measures are an important part of disease prevention.


M


Even if a producer has a “closed” herd, new bulls are purchased occasionally, to bring in new bloodlines. Thus, it is important to make sure those bulls are healthy, and not carrying a disease that a herd has not encountered.


Dr. Tom Hairgrove (Extension


Veterinarian, Animal Science, at Texas A&M) says producers need to be really careful when buying bulls to make sure they do not bring home reproductive diseases or some other disease. The risks are lower when buying young bulls from a reputable breeder or source, but this does not ensure that problems will not occur.


TRICHOMONIASIS


“Regarding Trich, virgin bulls under 12 months of age usually do not have to be tested, but you do not know for sure if it is a virgin bull. We have had many cases where so-called virgin bulls were infected, and they are not virgin bulls if they are infected. Some young bulls are mounting cows out in the pasture even before they are weaned. Those young bulls are supposedly not as likely to transmit Trich; they have about a 10 percent chance of transmitting the disease, compared with older bulls that have an 80 to 90 percent chance, but there is still a risk that a young bull could bring the disease into your herd,” says Hairgrove.


aintaining optimum herd


“You should test a new bull for Trich, but you also need to know about the history of that bull. One test is not always sufficient to know if the bull is actually negative. Is the bull harboring a sufficient 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 are not always going to pick up every positive bull,” he says. If there is an insufficient number of organisms in the sample or some contamination in the sample, even the most modern sophisticated molecular diagnostics (PCR test) will not pick up the infection. Careful handling of samples and meticulous attention to detail enhances chances for a good test.


“It’s amazing how infected bulls will vary from week to week in testing. 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 confidence that the bull is indeed negative,” says Hairgrove.


“If a producer tests a purchased bull and he is positive, that bull is definitely infected. But if the bull tests negative, that is no guarantee that he is actually negative. Bulls entering semen collecting stations are required to have six negative tests before collection,” says Hairgrove.


“What level of risk are you willing to accept? If you do not know the bull’s background, I recommend doing more than one test. It is an expensive test, but not nearly as expensive as dealing with Trich in your herd!”


Hairgrove has worked with several herds that have Trich and is trying hard to clean it up and get rid of it, but it


keeps showing up again. “Is it because of purchased cattle being infected? Is it because of mingling with infected neighboring cattle, or because a few cows carry it over into the next year even though they were able to carry a calf to term? The cows also play a role in the spread of this disease. So, we tell clients to test every new bull for Trich but also understand that a negative test is not 100 percent assurance that the bull is negative,” he says.


“If you buy bulls from a reputable breeder and you know his program and herd health history, one test would probably be adequate. But if you do not have good knowledge about that breeder’s operation, you might do multiple tests,” he says.


BVD


Another disease to be concerned about is BVD, Bovine Viral Diarrhea. You do not want to buy a bull from any herd that has BVD. “If there is enough virus circulating in that herd, especially in the young animals, you may end up with a bull that has a chronic testicular infection, or a persistent infection,” says Hairgrove.


“We want to know that a new bull is non- PI (persistently infected), but we also want to know his vaccination history. If a bull is exposed to the BVD virus before puberty, the virus can replicate in the testicles, and he will shed virus in his semen, sometimes for an extremely long period of time. There have been some issues in which breeders used a modified-live, non-cytopathic vaccine in young bulls (pre-puberty), producing prolonged testicular infection,” he says.


“The testicles are somewhat isolated from the rest of the body, and this


prevents a bull from developing a (cont’d)


2017 MARCH i TEXAS LONGHORN JOURNAL 25


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64