Bringing new cattle into the herd: Avoiding persistent but preventable diseases
Purchasing new herd replacements such as bulls, heifers, or bred cows creates the opportunity to improve a cow-calf operation’s genetic base. As we discussed in the previous column, however, these purchases also create the opportunity to bring in new infectious diseases.
I’ve previously emphasized the importance of a 30-day isolation period for incoming cattle, giving them time to recover from any move-related stress and to stop shedding germs they may have brought in. This doesn’t work for every disease, however. Unfortunately, there are several important cattle diseases that animals can carry and spread for life. These animals are termed “persistently infected.” For their diseases, there’s no isolation period that will ever be long enough.
These persistent infections can wreak havoc on a herd’s performance in ways that aren’t blatantly obvious until later. A prime example is Bovine Viral Diarrhea (BVD). This virus causes infertility, abortions, and birth defects. It also suppresses animals’ immune systems, increasing their risk for other illnesses. Should persistently-infected BVD animals enter a herd, they will expose their herdmates to enormous amounts of virus. If this happens during breeding and gestation, reproduction takes a huge hit – and more cows give birth to persistently infected calves, greatly amplifying a herd’s problems over time.
Neospora is an interesting infection that can also persist in cows and heifers. Heifers persistently infected with Neospora are more likely to suffer reproductive failure, while infected cows are more likely to keep their pregnancies. Calves that are carried to term are likely to be persistently infected as well, perpetuating the problem.
While neither are common in the northern plains, Lepto hardjo-bovis and anaplasmosis are persistent infections to also consider. Cattle brought in from southern states are more at risk for these diseases, both of which can spread through a herd and cause problems for years to come.
Trichomoniasis, a persistent venereal infection that can enter a herd through non-virgin bulls or temporarily infected open cows, should be mentioned too. State regulations take care of most of this risk for cattle producers, requiring non-virgin bulls to be trich tested on change of ownership, and prohibiting open cows from being sold into breeding herds.
If the risk of these diseases cannot be eliminated by isolating new animals, what can be done? A 30-day isolation is still a good idea, for the reasons discussed earlier. For these persistent diseases, the isolation period also gives us time to test or treat these new animals.
All incoming cattle should be tested for BVD persistent infection. This is as easy as taking an ear notch from each animal for lab testing. A quirk of BVD testing applies to bred heifers or cows. The dam herself can test negative, even when the calf she’s carrying is persistently infected. For that reason, bred animals should be isolated from the rest of the herd until they have their calves, which should be BVD ear-notched before turned out.
Blood samples can tell us an animal’s exposure status for Neospora and anaplasmosis. Because of their risk of reproductive failure, heifers are the target animals for Neospora testing. All replacements coming from anaplasmosis-endemic areas should be bled on arrival as well. Lepto hardjo-bovis is hard to test for, but can be cleared from the animal with treatments such as long-acting tetracycline. Anaplasmosis-positive animals can be treated in a similar manner.
Testing protocols should spark an important question to answer before the first sample is even taken: What are you going to do if the animals are positive? There’s no cure for BVD, trich, or Neospora. Are you willing to dump or separately manage those new animals? If the honest answer is no, then why test at all? This makes a case for asking seedstock suppliers to test their sale animals before they’re even offered.
Testing for these persistent diseases might seem like overkill to producers who have never had these problems in their herds. But considering all the things we can’t control in our herds (weather, a bull going bad, etc.), why not address these things we can control? Consider isolation and testing as part of the cost of bringing in your replacements this year, and have a talk with your veterinarian about the best way to do this for your own operation.
Russ Daly, DVM, is the Extension veterinarian at South Dakota State University. He can be reached via e-mail at email@example.com or at 605-688-5171.