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 does not get back into the general circulation and is therefore not exposed to the immune system. He will not test positive, but when he breeds a cow he could pass the virus to her. This infection in the testicles will not show up on an ear notch test when you are checking for persistent infection,” explains Hairgrove.
Anyone who keeps bulls for breeding should be aware of the possible problem that might be caused by vaccination (with modified-live, non-cytopathic BVD vaccine) before puberty.
“It is a good
idea to work with your veterinarian to know which vaccines you can safely use on bull calves.”
When buying a bull, the history of the bull is extremely important.
“If you do
not know much about him, you might want to look at some alternate tests. When I consult with ranchers, I tell them that they need to talk with their own veterinarians about this. It might pay to do a PCR test on the bull’s semen, for instance, if there are any questions,” says Hairgrove.
IBR
IBR, Infectious Bovine Rhinotracheitis, is another issue of concern that should not be introduced into a herd. This disease is difficult to diagnose by looking at blood titers. The animal may have a titer just from vaccination. The purpose of vaccination is to try to build titers (antibody protection) against the disease.
“In order to interpret a test for IBR, you need to know when the bull was vaccinated and with what product, and which lab did the test. There is valuable information to be gleaned from a blood
test, but different labs will use different numbers. Your veterinarian will hopefully know how to interpret these. IBR always has a potential for future problems; this is a herpes virus that can go dormant and become active again later during a time of stress, similar to shingles cropping up in humans who had chicken pox years earlier,” says Hairgrove.
ANAPLASMOSIS
A bull has more contact with a herd than any other individual animal, so there is more opportunity for him to spread disease if he has some type of infection. “He will have more contact - cow to cow to cow. This is what we are seeing with our anaplasmosis study. On one ranch, we have a 25 percent prevalence of carrier state in the cows, but we have 90 percent carrier state in the bulls. It may be because they have more contact with all the cows. We are wondering if it has to do with their social structure. I looked at the incidence of carrier status on another ranch, just out of curiosity, and sure enough, about 80 percent of the bulls were sero-positive compared to only about 30 to 40 percent of the cows,” he says.
“If I am buying a bull, depending on whether I am in an area where anaplasmosis is prevalent or not, this is something I would want to know. If I brought an infected bull into a non- infected herd, this disease might spread quickly - especially if there are vectors such as ticks or biting flies,” says Hairgrove.
“If anaplasmosis is uncommon in your area, and bring in a bull from an area where this disease is common, he may be a carrier and expose your herd. You do not want to inadvertently add to this risk when working cattle; if the bull is part of the group when you are vaccinating and you do not change needles, or fly-tagging without disinfecting the
26 TEXAS LONGHORN JOURNAL i MARCH 2017
instrument between animals, you may spread the disease.”
JOHNE’S DISEASE
Some diseases are very difficult to detect in early stages, and a carrier animal that appears healthy might be brought in. Johne’s disease is probably the most extreme example. Again, herd health history is important to know when purchasing a bull. “With Johne’s disease, the bull becomes infected when he is a calf, but it probably will not show up until he is 5 years old or older,” says Hairgrove.
Although infected, the young bull will likely test negative at purchasing time, and will not test positive until years later. A breeder might sell him before the bull shows any clinical signs of Johne’s. In the meantime, he may have infected a herd and the breeder will have no idea of the source of infection.
“If the bull has Johne’s and is stressed during breeding season, he may start shedding the pathogen.” It is important to know as much as possible about the background and have faith in the breeder who raised them.
The typical quarantine routine for biosecurity will not help in this type of situation. “I could keep a bull quarantined the rest of his life, and he is not going to show any signs of vibrio or Trich, and may not show any signs of Johne’s until he is many years older. So, for some diseases, we need to test as well as quarantine.” It is wise to discuss all of these possibilities with your veterinarian before turning a bull out with the cows after a simple three-week quarantine.
“Some people figure they can just test the bull for all these diseases, but for Johne’s this may not be adequate. Tests for Johne’s are not reliable in the early
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