Buying animals into the herd may be required to enhance genetics or for recipient purposes. There are risks associated with adding animals of unknown health status to your herd. Biosecurity is a buzzword that refers to management practices that protect the herd from new diseases, and reduce the spread and adverse effects of those diseases in the herd.
ALL herds are susceptible to infectious disease. Remaining a closed herd, in which no new cattle are brought onto the premises, reduces risk. There are very few truly closed herds. Show attendance, wildlife, vehicle and people traffic, and the potential necessity for buying replacements all contribute to the exposure of your herd to disease.
The goal, of course, is to keep the herd secure against all disease. Protection is safer, simpler and much more economical than treatment or elimination. Clinical mastitis is an obvious disease. But hidden diseases, diseases not apparent when replacements arrive, can also be expensive if unleashed in an unexposed herd. These include subclinical mastitis, infectious bovine tracheitis (IBR), bovine virus diarrhea (BVD), Johne’s disease, bovine leukosis virus (BLV or EBL), and Neospora.
Vaccination status – Most herds on herd health programs are on regular vaccination schedules. Vaccinating develops and maintains herd immunity to viruses such as IBR, BVD, BRSV (bovine respiratory syncytial virus), and PI3 (parainfluenza-3), and to the bacteria Leptospira sp. and Hemophilus sp. Make sure your herd immunity levels are high before adding cattle. Adding cows that carry an IBR virus or a BVD virus into closed herds with low immunity levels to these diseases has been disastrous. ASK about the status of new additions, and ENSURE that you adequately protect your herd with a complete vaccination program.
Bovine leukosis virus infects the immune system in cattle of all ages. The BLV virus can cause clinical disease. It is a persistent infection, meaning that once cattle are infected, they are permanent carriers. There is no vaccine or treatment for BLV. Effects on overall production are difficult to assess, but there is increasing evidence that leukosis positive animals have less competent immune systems. A negative serum test for incoming cattle is the only sure method of preventing infected new additions. Test animals before purchasing or on arrival.
Both vertical and horizontal transmission occurs with BLV. Knowledge and application of control measures such as single-use needles, equipment disinfection, and colostrum management should be standard for your farm.
Neospora is a single cell parasite and a cause of abortions in the Fraser Valley. Research continues but unknowns remain about this disease. There is no evidence of horizontal transmission from cow to herdmate; however, there is a 90+% vertical transmission rate from dam to calf. Research also shows that we cull Neospora seropositive cows at a much higher rate than negative cows whether they abort or not. Specify seronegative animals when purchasing.
Johne’s disease is a chronic intestinal infection caused by the bacteria Mycobacterium paratuberculosis. The disease is spread through the ingestion of feces. Infection usually occurs before six months of age, but the disease rarely becomes apparent before three years of age. Infected animals that are clinically ill have persistent diarrhea, weight loss, and decreased milk production. Subclinically infected animals have lower milk production, lower reproductive efficiency, and increased susceptibility to mastitis. Researchers estimate that 10 subclinical or hidden animals exist for every clinically ill animal in any given herd. The potential economic losses of Johne’s can be very large.
While these economic losses alone justify concerted efforts at control, there are other incentives as well. Researchers have found that the bacteria causing Johne’s disease are similar to the bacteria causing Crohn’s disease in humans. No direct link is known. Herd health status concerns are similar to BLV for cattle and embryo exports. Addressing potential human health concerns should motivate all to prioritize Johne’s control.
Diagnosis of Johne’s involves using laboratory tests that are half as accurate and twice as costly as most other serum tests. Sensitivity uncertainties with single serum tests and inconclusive results in animals less than one year old are additional problems. Purchased animals should have a negative test or be from a negative herd. Retesting is advised.
Summary
Biosecurity goes beyond obvious animal health. Keeping diseases off the farm results in healthier cows, more profit and fewer headaches. Although home-grown replacements are the safest source for maintaining or increasing herd size, this is not always possible or practical. Biosecurity is equally important for adding two cows or for a major 100-cow expansion. When bringing in new animals, the key control points are:
Buy safely. Proven udder health and negative tests for BLV, Neospora, and Johne’s are all reasonable requests.
Isolate and observe new entries. This is perhaps not practical for milking cows, but certainly possible for heifers and springers. Recipient management includes attention to biosecurity. All animals should be entered in the herd’s vaccination program. Animals with unknown status for the above diseases should be tested.
Set up management and sanitation practices that promote biosecurity within your herd. This protects all animals from diseases shed by newcomers and any unknown positives already in the herd.
