You have the tools in hand to stop this virus from spreading. Small changes in your management practices hold the key to success.

BLV is spread by infected blood, and from dam to calf during gestation. Once an animal contracts the virus, it opens the door for cancer to develop. Clinical signs the signs you can see by looking at an animal generally occur in mature cows in their third lactation and beyond. But just because you don't see BLV doesn't mean it's not in your herd.

If you ignore this disease, more animals will become infected. Once enough animals become infected about 30 you"ll start to experience financial losses. For example, a cull cow will no longer breed back because of cancer in her reproductive tract.

These aren't the only types of losses, however. The other monetary losses come from the lost sale of breeding stock, semen and embryos from BLV-infected livestock, especially in countries where BLV-Eradication programs are already in place.

Once you receive the results from the lab, separate the animals into pens according to which test positive and which test negative, says Shirley, who designed the BLV eradication program for the Kansas State University dairy. If separation is not practical for all of the cows, milk the BLV-positive ones last.

With heifers, it is best to segregate the BLV-positive animals from the BlV-negative animals. Doing so helps you raise disease-free replacement heifers, says Mike Brunner, Cornell University extension dairy veterinarian who works with the New York State BLV Eradication Program.

• Use sterile, single-use disposable needles for all injections.
• After each animal, rinse and disinfect instruments used for tagging, castrating, tattooing, removing extra teats and dehorning. Use water to spray off any excess debris and then soak the tool in household bleach. It works best to have two taggers, for example, and to have one soaking while the other one is in use. After one instrument has been used, switch to the one that's been soaking, suggest Brunner.
• Consider using bloodless dehorning options, such as an electric hot iron or caustic paste.
• Remove extra teats, insert ear tags and dehorn calves while they are housed individually.
• After dehorning animals, keep water and feed sources free of blood.
• Do not allow calves from dams that test positive to have contact with other animals until they have been tested. (You can draw blood for a test before a calf nurses, or you feed colostrum to get immediate results, or wait until it reaches seven months of age.)
• Do not feed colostrum or milk from BLV-positive cows to calves, says Shirley. If you only feed colostrum from BLV-negative cows, calves can be tested right away.
• At the 500-cow Carnation Farm in Carnation, Wash., Erich Studer, the director of veterinary medicine, has employees pasteurize all milk fed to calves. The pasteurization kills the leukosis virus in lymphocytes and prevents the transfer of the virus to the calves, he explains. Studies have shown that pasteurization becomes cost-effective when you feed 300 or more calves each year. (For more on pasteurization, see the story "Pasteurization calf milk pays," in the October 1996 issue of Dairy Herd Management.)
  

Management practices can make or break disease control in the dairy industry today, say Studer. For example, at Carnation Farm, the first four years of testing and management control practices resulted in a decline in herd prevalence from 23 percent to 11.8 percent. However, the introductions of 99 purchased cows (which were not tested for BLV prior to purchase) increased herd prevalence up to 24 percent again. Now, Studer tests all animals for BLV before purchase.

In addition to milking BLV-positive cows last, you also need to:

• Use a separate obstetric sleeve for each animal. At a minimum, use a separate sleeve for each animal, which tests negative for BLV.
• Cold sterilize calf delivery equipment by pouring rubbing alcohol or nolvasan on it before each use.
• Use artificial insemination for all breedings.
• Use sterile, single-use disposable needles for all injections.
• Use a separate calving pen for each cow. Clean and disinfect between cows.
  

• Perform all veterinary procedures on BLV-positive animals last.
• Store intravenous tubing or needles in a disinfectant solution such as chlorhexidine.
• During the first year of your eradication program, test at least twice, preferably three times. After that, test all negative animals annually. The blood test will cost $3 to $5 pretest, depending on where you have it done, so you don't want to waste money retesting, positive animals their status won't change. Animal testing will tell you if your control measures are working.
• Control biting insects
• Test all herd additions for BLV before they enter the herd.
• In all animal-handling procedures, such as hauling to pasture or working through a chute, BLV-negative should be processed first.
• When possible, use BLV-positive as a factor in culling animals. However, Brunner acknowledges that most producers are not in a position to cull all positive animals at once.
• Use ear tags to mark all positive animals. That way, if an animal gets out of its pen, it won't accidentally get put in with BLV-negative animals simply because it was near that pen.

The rate of progress made eradicating this disease varies from farm to farm. Granted, you'll make faster progress if you adopt all of these changes, but for some of you that may not be feasible. Your first goal is to stop the spread with in your herd. Once you do that, then you can focus on eliminating BLV from your herd. How fast you do it is up to you and your veterinarian.

2. Blood transmission.
Research has shown that small amounts of blood as little as 1/10 of a drop of blood on a needle can lead to BLV infection. Management practices such as dehorning, vaccinating, and ear tagging also can transfer BLV from animal to animal. So can biting insects.