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Biosecurity: Tips on Bring Home a New Bull

By Heather Smith Thomas

For most new bulls, the quarantine period is simply the ride home. Three weeks is better.

One of the most common ways new diseases come into a herd is with new animals. Biosecurity measures are an important part of disease prevention, along with good nutrition and vaccination.

Dr. Ron Gill, Texas A&M AgriLife Extension associate department head, says the things you'd need to worry about will depend partly on the age of the bull and what he has been exposed to, and whether he's been with cows. A vital partner in evaluating a new bull purchase is your veterinarian.

"Always work with your veterinarian on this and in getting your new bulls in synch with your herd health program," says Gill.

Breeding-related diseases

Dr. Tom Hairgrove, Texas A&M AgriLife Extension veterinarian, says producers need to be careful when buying bulls to make sure they don't bring home reproductive diseases. The risks are lower when buying young bulls from a reputable breeder or source, but this does not guarantee that there won't be problems.

Trichomoniasis is a costly disease that you don't want to bring into your herd via an infected bull. "Bulls in Texas are required to be tested before they change ownership or possession, unless they are under a certain age," says Gill. "Many people assume young bulls are virgin bulls, and that's usually a mistake. Most young bulls have had opportunity to be with cows," he says.

Hairgrove points out that it's hard to know for sure a bull is virgin.

"We've had many cases where so-called virgin bulls were infected with trich — and they are not virgin bulls if they are infected. Some young bulls are mounting cows out in the pasture or on the range 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 a herd," says Hairgrove.

"If a person is buying bulls of any age that have been exposed to cows, Texas regulations require 1 test, but 1 test is not adequate," says Gill.

"The Texas Animal Health Commission (TAHC) is managing a control program and not an eradication program. As a ranch, you need to manage for prevention or eradication of this disease. There are some false negatives that show up with either the culture or the PCR test, so it takes more than 1 test," he says.

The tests need to be run a minimum of twice, and preferably 3 times, at least a week apart to know if the bull is actually negative before he is put with cows. With 3 negative tests, a person can be 99 percent sure the bull does not have trich. "Very few ranchers are doing multiple tests, however, so now we are finding 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 working on a research project, bringing some infected bulls to the college to study — to look at some of the variables when testing bulls for trich.

"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 do not always pick up every positive bull," he says.

If there are insufficient numbers of organisms in the sample or some contamination, even the most sophisticated molecular diagnostics (PCR test) will not pick up the infection. Careful handling of samples and meticulous attention to detail enhance chances for a good test.

"It's amazing how the infected bulls will vary from week to week. We are not finished yet with our study project, but we've done enough testing around the state to know that 1 test is not always sufficient. 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 the bull tests positive, that bull is definitely infected. But if the bull tests negative, that's no guarantee 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 first test was negative? What level of risk is a producer willing to accept? If the producer does not know the bull's background, I recommend 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. "Often 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 not been tested, or you don't know if he's been tested, I would recommend 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 battery 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 semen," he says.

Hairgrove says a person needs to make sure that a new bull is not persistently 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, sometimes for an extremely long time. There have been instances in which producers 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 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 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. "There are some research papers that support this warning. It's a good idea to work with your veterinarian to know which vaccines you can safely use on bull calves," Hairgrove says.

When buying a bull, you need to know the history of the bull. "If you don't know much about him, you might want to do some tests. When I consult with producers 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

This virus is another concern. "IBR is more difficult to test for if you are looking at blood titers," says Gill. "The animal may have a titer just from vaccination. You are trying to build titers (antibody protection) against the disease. Unless the titer is really high, you don't know whether it's from natural exposure they've recovered from or from vaccination," he explains.

"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," says Hairgrove.

"There is valuable information to be gleaned from a blood test, but different labs use different numbers and your veterinarian, it is hoped, will 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

"Some of the problems we've seen in bulls brought into Texas or moved from one region of Texas to another is anaplasmosis," says Gill. If bulls were raised in an area where this disease is endemic, they may be carriers even if they don't express any signs of disease. If they are introduced into a cow herd that is naïve to anaplasmosis, there is risk that anaplasmosis will spread through the cows.

The reverse is also true. "If a naïve yearling or 2-year-old bull is put with a herd of cows that carry anaplasmosis, you could lose the bull. Either of these situations can be a serious issue, so you need to know the herd status," he says.

Gill recommends that bulls coming into a herd be tested to see if they do have anaplasmosis. "Most people don't test the bulls, but we've seen more issues these past 3 or 4 years with bulls that have been moved from areas where anaplasmosis is an issue."

Hairgrove points out that a bull has more contact with your herd than does 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 current anaplasmosis study.

"On one ranch we have a 25 percent prevalence of carrier state in the cows, but 90 percent carrier state in the bulls. I'm thinking it may be because they have more contact with all the cows, but at this point we don't really know.

"I looked at the incidence of carrier status on another ranch, out of curiosity, and about 80 percent of the bulls were sero-positive compared to only about 30 to 40 percent of the cows. Again, there was higher prevalence in the bulls and we're not sure why. Maybe the bulls were in a pasture with more ticks during the off-season," he says.

"If I am buying a bull, depending on whether I'm in an area where anaplasmosis is prevalent or not, the bull's status is something I'd want to know. If I brought an infected bull into a non-infected herd, this disease might be spread pretty fast — especially if there are vectors such as ticks or biting flies," says Hairgrove.

"Also, you don't want to inadvertently add to this risk when working cattle. If the bull is part of the group when you are vaccinating and you don't change needles, or if you are fly-tagging without disinfecting the instrument between animals, you may spread the disease," Hairgrove says.

Johne's disease

This is a serious disease that generally infects cattle at an early age if they are exposed to the pathogens shed in manure from carrier cows. It takes years, however, before signs of the disease show up — with weight loss and diarrhea. A bull might be infected and you'd never know it, but he could introduce this devastating disease to your herd.

"If you can buy bulls from herds that are certified Johne's free, this is best," says Gill. "It's almost impossible to test for this in young animals, such as a yearling or 2-year-old bull. They generally aren't shedding the pathogen yet, until they are 4 or 5 years old. A bull might be brought in with Johne's and be sold (replaced with a younger bull) before he ever shows clinical signs of this disease. You might never know that he was the animal that brought this disease to your herd," says Gill.

If the bull has Johne's and is stressed during the breeding season he may start shedding the pathogen. If you are buying any cattle, it's important to know as much as possible about their background and have some faith in the breeder who raised them. People buy bulls from various sources and don't always know much about the history of the herd of origin.

The typical quarantine routine for biosecurity won't help in this situation.

"When I ask producers what's the most important biosecurity factor, they usually mention quarantine," says Hairgrove. "I could keep a bull quarantined the rest of his life and he's not going to show any signs of vibrio or trich, and may not show any signs of Johne's either, until he is many years older. So for some diseases we need to test as well as quarantine." It's wise to discuss this with your veterinarian before turning the bull out with the cows after a 3-week quarantine.

"Some people figure they can just test the bull for diseases, but for Johne's this may not be adequate. Tests for Johne's are not very reliable in the early stages of the disease — before clinical signs like weight loss (in spite of good appetite) and diarrhea appear. As the animal gets closer to the end stage, the test is also not very reliable. We can't assume the test will tell us whether or not the animal has Johne's."

Bovine leukosis, leukemia, bluetongue

"If a producer has a closed herd, it's worth the effort to try to keep out some of the diseases they don't already have, and this might include bovine leukosis," says Hairgrove.

"Commercial producers might not be too worried about this one, especially if they don't know the status of their herds. Bovine leukosis is fairly common, but it's something you don't want if you don't already have it. When I brought bulls here to the vet school for the research project on trich, bovine leukosis was one of the things they had to be tested for to come here."

You could talk with your veterinarian to discuss things like leukosis, to see if this might be a risk. The diseases you might worry about or not worry about will often depend on your own herd situation, where you are located, etc.

There are some trade issues in which other countries won't let you import cattle unless they are tested for various diseases including bluetongue. "If you are in an area where this disease does not occur, and you buy a bull that might have bluetongue, he should be tested. These are questions you could discuss with your veterinarian because these issues will vary in different parts of the country," he says.

Parasites

"Make sure a bull is not carrying any internal or external parasites before he goes out on your pastures or mingles with your cattle," says Gill. "You should get him in sync with your own deworming and delousing program. We've seen some instances where people brought in bulls that were loaded with parasites and they didn't know it, and undermined their deworming programs."

A new bull may bring parasites that are resistant to commonly used deworming drugs. "We know there are some serious resistance issues in sheep and goats, and now we are concerned about resistance problems developing in cattle," says Hairgrove. "If I am bringing in any new cattle, this could be a concern, but especially when buying a bull because he will cover more country and have more potential for spreading parasites."

"It pays to take a fecal sample while you still have him quarantined (before he goes out with the cows), deworm the bull, and then check a fecal sample 3 weeks later," Hairgrove says. "Then you will know whether or not your product is doing a good job on those parasites. If the bull is still wormy 3 weeks after you treat him, this means your product didn't work very well and you need to find something that will deworm him adequately before you turn him out on your pastures. Otherwise you'll be increasing the risk for parasite resistance in your herd."

Depending on the time of year you buy the bull, you may also want to check him for lice or mange mites. "Most of these external parasites are seasonal and fairly self-limiting, but there's no need to add them to your herd if your cattle don't have them."

It's always a good idea to know the history of new animals and/or do some testing and checking before they are put into your own herd. All too often when a herd ends up with a problem it was because of a new animal that was brought in. "By the time we get to the wreck we may not know where we got it," says Hairgrove.

Quarantine

We often talk about keeping new animals quarantined for a certain period of time. "For most new bulls, however, the 'quarantine' period is simply the ride home," says Gill. A 3-week quarantine may be adequate to know if the bull was exposed to some types of diseases in which he might show symptoms soon, but for diseases like trich, BVD-PI, Johnes, etc. this won't help.

The quarantine time is important, however. It gives you a chance to know if the bull is coming down with some types of contagious disease and gives you time to vaccinate him. It's wise to vaccinate incoming bulls for all major diseases, including clostridial diseases.

"A lot of people don't vaccinate their bulls and end up losing a bull. The quarantine period is when you can get all your vaccines into those bulls and make sure they are on your health program. Trich tests should have already been done, but if not, you can make sure it gets done, and do any followup testing," Gill says.

There is a big advantage to buying bulls well ahead of when you plan to turn them out with the cows. "Many people buy young bulls at a sale in March and turn them out in April and haven't had time to do anything with those bulls. I personally like to buy a bull in October and have him ready for the next spring. This not only gets him on the same herd health program as the cows, but gets him toughened up and ready to go to work," says Gill.

 

 
 

"Bull Biosecurity" is from the October 2013 issue of The Cattleman magazine.