Thanks to Bill Elkins for this helpful article!
In the summer of 2009 we had a wreck in our Angus cow-calf program (Buck Run Farm) in Southeast PA. Yearlings did not grow, heifers did not breed. It was hot alright, and we have plenty of toxic Tall Fescue. Summer slump was not new to us, but this was something else again. We were looking at 4-500 pound yearling weights and 200 pound weaning weights; about 100% below normal. Preg checks in early fall showed mostly open cows and confirmed imminent disaster. Our vet, Dr. Billy Smith, of the University of Pennsylvania Veterinary School, called for ear punch biopsies for the entire herd. He suspected Bovine Viral Diarrhea was the problem in spite of the fact that we had a rigorous vaccination program in place for many years.
Well, he was spot on. Biopsies from 3 spring calves were loaded with BVD virus. As is not uncommon, these 3 appeared no worse-off than their contemporaries. But they were apparently sending viral challenges to the rest of the herd so that they spent the summer fighting off these challenges rather than growing and breeding.
Once the 3 offenders were dispatched, the herd bloomed. We continued testing all newborns in the following three calving seasons and found one more with a positive BVD test. Of course his time in the herd was much shorter than the first three, so he could do little harm – that is unless he encountered a female about 100 days pregnant and infected her fetus. Calves infected in utero at about 100 days gestation are rendered persistent infected (PI) to BVD. Their immature immune system is just learning to distinguish “self” from “not-self” at this time, and so it “thinks” that BVD is a normal constituent of “self,” and cannot get rid of the virus in later life. PI calves may appear normal but are the source of infection to others.
Our herd had been closed for 6 years except that I allowed a young man, who wanted to start his own herd, to bring 5 head on the place in 2008. These were vaccinated (but not biopsied) and were quarantined for several months with no apparent health issues before being allowed in with our own herd. This was about a year before the wreck started. They all left before we knew what was going on, so it was not possible to get them biopsied. Thus, we don’t know for sure whether they were the source of our problem. Coincidence raises suspicion but does not establish cause. It’s also possible that we had been unknowingly raising PI calves in earlier times. They were sold without our knowledge of their PI status before they could cause a wreck, but NOT before passing the virus to a susceptible fetus, thereby setting the stage for on-going trouble.
It’s not uncommon for cow-calf operators to skimp on vaccination, and I was often tempted to save dollars that way. I knew that BVD and the like were out-there, but I was not aware of a case in any of my neighbors’ herds, and the threat seemed remote. Luckily, my vet persuaded me to stay with it. If I had not, I doubt that I would still have a breeding herd.
You might wonder then how our religiously vaccinated herd got in trouble. If BVD is brought to the herd from any unknown outside source such as wildlife, it may cause transient infection in some animals, especially those in which prior vaccination gave less than optimal immunity. If there are 100 day pregnancies in the herd at the same time, PT calves may result. A vaccinated herd might suffer temporarily, even severely as in our case, but the havoc in an unvaccinated herd would likely be much worse. Nothing’s perfect, but I believe that vaccination tips the odds big time in your favor and is well worth the cost.
Editors Note: An article in the May 18, 2013 edition of the Veterinary Record reports that BVDV was successfully eradicated from Norwegian herds. The Norwegian project was a collaborative effort of the Norwegian Animal Health Authorities (NAH), the National Veterinary Institute, the cattle owners and three farmers’ associations. They tested and culled herds from 1992 to 2004. The last four PI cattle were found in the same herd in 2005 and were culled. Since then they have continued surveillance but have not found any more infected animals. Until the program eradicated the disease from their herds, producers were suffering direct losses of about $8 million per year. That makes the $8.7 million total cost of the 10 year project well worth it! So, what are the chances that we could learn from the Norwegians to implement our own BVDV program?