Post by simplynaturalfarm on Apr 4, 2014 18:03:42 GMT -5
If one chooses to purchase a cow based on a negative PCR for it, then they don't realize that Bovine leukosis can exist in the absence of viremia. We KNOW that cows can be positive while showing a negative PCR. BLV infects individual white blood cells and so although the PCR test is very accurate, it is the luck of the draw whether the sample you take is going to have an infected lymphocyte in it. The only way a PCR test will turn up positive on a blood sample is if you had virus there. So in theory a cow could have the virus in their system somewhere and not come up positive on the pcr test. So when it turns up positive on PCR you can be VERY sure it is positive, but you can't trust a negative. You can trust a negative antibody test (elisa) more than you can trust a negative PCR but it is not 100%.
When it comes to using an individual PCR test for purchase from a herd that doesn't test, it is not the most helpful in the world. Multiple negative Elisa tests will be beneficial OR a positive PCR. But really these tests were made for use every 6 months, along with management - you are supposed to confirm negatives with multiple tests, and test every animal over the age of 6 months every 6 months. A single test is not that beneficial, especially when you realize how very little it takes to spread it - one single lymphocyte! It is spread via flies (yes it is), it is spread via milking (as it is a lymphocyte and those are found in the milk and you can cause spread diseases by using same machine on cows), it is spread by use of same sleeves at palpation, horn removal, tatooing, vaccination and shared needles, contaminated vaccine bottles, calves can get it in utero, via colostrum that is not frozen or heated etc.
So when it comes to being sure you buy a BLV negative cow, it is way better to purchase from a place that does testing every 6 months and maintains excellent controls - no shared needles, proper hygeine for colostrum etc, because testing the herd once is not going to prove it does not exist. Especially depending on the tests you use.
PCR cost is $35 from the lab. Every vet charges for their time, the shipping and then profit on top. So you can count on $70ish for one test that if it is negative is not negative. THe elisa costs $6.00 and you can run repeats and lows for another $6.00. That is why vets do not simply tell everybody to do PCR - it is not that simple nor cut and dried.
When it comes to using an individual PCR test for purchase from a herd that doesn't test, it is not the most helpful in the world. Multiple negative Elisa tests will be beneficial OR a positive PCR. But really these tests were made for use every 6 months, along with management - you are supposed to confirm negatives with multiple tests, and test every animal over the age of 6 months every 6 months. A single test is not that beneficial, especially when you realize how very little it takes to spread it - one single lymphocyte! It is spread via flies (yes it is), it is spread via milking (as it is a lymphocyte and those are found in the milk and you can cause spread diseases by using same machine on cows), it is spread by use of same sleeves at palpation, horn removal, tatooing, vaccination and shared needles, contaminated vaccine bottles, calves can get it in utero, via colostrum that is not frozen or heated etc.
So when it comes to being sure you buy a BLV negative cow, it is way better to purchase from a place that does testing every 6 months and maintains excellent controls - no shared needles, proper hygeine for colostrum etc, because testing the herd once is not going to prove it does not exist. Especially depending on the tests you use.
PCR cost is $35 from the lab. Every vet charges for their time, the shipping and then profit on top. So you can count on $70ish for one test that if it is negative is not negative. THe elisa costs $6.00 and you can run repeats and lows for another $6.00. That is why vets do not simply tell everybody to do PCR - it is not that simple nor cut and dried.