by: Heather Smith Thomas

Maintaining optimum herd 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 that new diseases come into a herd is with new animals. Biosecurity measures are an important part of disease prevention.

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 your herd has not encountered.

Dr. Ron Gill (Associate Department Head, Extension, Texas A&M) says the things you'd need to worry about will depend partly upon the age of the bull and what he has been exposed to, and whether he's been exposed to cows or not. “Many people make the assumption that young bulls are virgin bulls, and that's usually a mistake. Most young bulls have had opportunity to be with cows,” he says.

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 – Trichomoniasis is an issue in some herds, and this is something you certainly don't want to bring into your herd via an infected bull. “Bulls are required to be tested before they change ownership or possession, unless they are under a certain age. If a person is buying bulls of any age that have been exposed to cows, some state regulations require multiple tests while others require only one test, but one test is not adequate. 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 one test,” says Gill.

The tests need to be run a minimum of twice (and preferably three tests), at least a week apart, to know if the bull is actually negative before he is put with the cows. With three negative tests, a person can be 99 percent sure that the bull does not have trich. “The multiple tests are something that nobody is doing, however, so now we are finding more and more bulls introducing trich to the cow herds they are coming into,” he says.

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 and IBR – 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 PI (persistently infected) with BVD or not. We've seen some bulls come into a producer's herd that looked really good, showing no signs of BVD, but then we find out they are 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 PI is not common, but it can happen. BVD is certainly a disease you don't want to bring into your herd. “This is easy to test for, and if your veterinarian is going through a battery of tests for the bulls this is something you ought to 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.

IBR is another issue of concern. “This is more difficult to test for, looking at blood titers. 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.”

Anaplasmosis - “Some of the problems we've seen in bulls brought into Texas or moved from one region of Texas to another is anaplasmosis. If bulls were raised in an area where this disease is endemic, those bulls 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,” says Gill.

The reverse is also true. “If a naïve yearling or two-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, one way or the other,” 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 three or four years with bulls that have been moved from areas where anaplasmosis is an issue.”

Johne's Disease – This is a serious disease that generally infects cattle at a young 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. It's almost impossible to test for this in young animals, such as a yearling or two-year-old bull. They generally aren't shedding the pathogen yet, until they are four or five 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 Brought This Disease To Your Herd,” Says Gill.

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. 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,” says Gill.

Quarantine – We often talk about keeping animals (new bulls, new cattle of any age coming onto the ranch) quarantined for a certain period of time. “For most new bulls, however, the ‘quarantine' period is simply the ride home,” says Gill. A three-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, PI BVD, Johnes, etc. this won't help. You could quarantine bulls for their whole life and it might not show up.

The quarantine time is important, however. It gives you a chance to know if the bull is coming down with a contagious disease, and also gives you time to vaccinate him. It's wise to vaccinate incoming bulls for all major diseases, including clostridial vaccines. “A lot of people don't vaccinate their bulls, and end up with bulls getting a clostridial infection and losing the bull. This is a cheap vaccine. When you bring bulls home, the quarantine period is when you can get all your vaccines into them 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 follow-up testing. A bull might pass the initial test, but I recommend re-testing at least twice for trich,” he says.

There is a big advantage to buying bulls well ahead of when you plan to turn them out with the cows. Sometimes a bull becomes injured and you have to replace him quickly, but in most cases you want your bulls home for awhile before you need to use them. “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. If he's been on a concentrate feed this gives his rumen a chance to adapt and get back on a complete forage diet,” says Gill.

“We see a lot of young bulls fall apart after they are brought home and turned out. They've been fed well and then get turned out and don't eat much while they are chasing cows, and lose weight and health.”

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