Too many dairy farmers have a false sense of security when it comes to BVD. They may “think” their vaccination regimen is protecting their herd, when, in fact, it’s not.
In this article, Ron Schultz, a specialist in veterinary infectious diseases at the UW-Madison vet school, continues an examination of bovine viral diarrhea (BVD).
Off the bat, Schultz wants to clear up some misconceptions about BVD, two of which surfaced in an earlier article in this series with Don Sockett, a vet at the state animal health lab in Madison.
First, Schultz clarifies, passively acquired BVD antibody present in colostrum and provided to the calf at birth does interfere with BVD vcaccines. He says the BVD antibody the calf receives from its dam in colostrum prevents BVD vaccines from immunizing for up to six months after birth in some calves.
Maternal antibody interferes in approximately 50% of Wisconsin dairy calves for up to three months. Prior to one month of age, it would interfere in 100% of calves. Thus, notes Schultz, “vaccination at less than a month is a waste of time and money in a majority of dairy calves that remain on the farm and are raised as replacement animals.”
Sockett, in the earlier article, also said that calves 2 to 5 weeks, don’t respond well to the BVD vaccines. Schultz says that leaves the impression that those less than two weeks and more than five weeks do respond well.
“This is not the case just described. Most calves less than two months of age (less than 50%) that receive colostrum won’t respond, because the passive antibody from colostrum interferes with vaccination,” says Schultz.
“Importantly, the BVD antibody from colostrum should protect the calf from infection with BVD. Thus you don’t need to vaccinate. That is one of the reasons it is so important that the calf receives as much colostrum and as early in life - less than two days old and preferably at birth - as possible,” he adds.
Therefore, Schultz says the recommendation for BVD vaccination should be: “The earliest to vaccinate is 2 to 3 months of age.
“When you use a modified live vaccine, one dose at this age is enough. If you use a killed vaccine, two doses are required, and the interval between doses should be 2 to 4 weeks.
“But you can’t stop there because most animals will not be immunized. You must give the vaccine again at 5 to 7 months - six months preferred - since at these ages, all calves will have lost any BVD antibody they received from the colostrum, and the vaccine should immunize,” he says. “If you use a modified live vaccine, one dose is enough at this age. If it is a killed vaccine, you need two doses with a 2 to 4-week interval between doses. Follow this program whether you vaccinated earlier or not, because the earlier vaccinations may not have worked due to interference by the BVD antibody from the colostrum.”
“I then recommend a revaccination be given again around one year of age. If you have given a vaccination (one dose of modified life vaccine or two doses of killed) at approximately six months, then you need only one dose of modified live or one dose of killed,” he states.
“If you have only vaccinated earlier than six months (for example, at three months) or haven’t vaccinated at all prior to one year, you need one dose of modified live vaccine or two doses of killed at one year.”
Schultz says that after the vaccination at one year, you really shouldn’t have to revaccinate more often than yearly, and then you need only give one dose of vaccine - regardless of type.
However, if you buy an animal over a year of age and don’t know the vaccination status, one dose of modified live is fine, but two doses of killed should be given with that 2 to 4-week interval between the doses.
“Never vaccinate pregnant animals with a modified live BVD vaccine!” Schultz warns.
This BVD expert says his “ideal” vaccination regimen for BVD is to vaccinate at 6 and 12 months with a modified live vaccine. “I like modified live. There’s nothing more effective,” he notes.
“A single dose at those two times provides the kind of immunity that if everyone would do it, they’d have a well-vaccinated herd,” he states. “They can be sure there won’t be interference from maternal antibodies (at that first vaccination at six months),” he notes. In contrast, if a farmer vaccinates calves at three months, he’s probably only effectively vaccinating half of the calves or less.
He recommends annual revaccination, for convenience, with a killed product. You can do the whole herd at one time that way. “You can go modified live, but not on the pregnant animals, so in that case, you end up vaccinating all the time.” He doesn’t recommend anything more than annual vaccination for BVD, because it’s hard on the cows, and can decrease production and put them off their feed.
To protect those young calves from IBR/PI3 , give an intranasal vaccine at 1 to 2 months of age if you want. Maternal antibodies from the colostrum don’t interfere with vaccines given intranasally. “You’re covered then,” says Schultz of 75% to 90% “immunization” intranasally. “The maternal antibodies can’t get up into the mucosal surfaces of the respiratory tract.”
Schultz reiterates the killed vaccine scenario - shots at 6 and 12 months, with two doses at six months old, given at 2 to 4 week interval, and one dose of killed vaccine at 12 months of age. “If you’ve given two doses at three months, you’ll still need two doses at six months,” he warns.
The problem with using killed vaccine - and where many farmers fall short of protecting their herds with it - is that if they either don’t give the second dose or don’t do so within that correct interval, they haven’t actually immunized their animals. “They’ve been vaccinated, but they’ve never been immunized,” he states.
The first dose of a killed vaccine “sensitizes” the animal for an immune response. It’s the second dose that actually induces the immune response.
He says there’s “less room for error with modified live.” “You’ll look awfully smart with modified live,” he quips.
Another plus for modified live BVD vaccine is that it protects against Type II BVD as well. “There is much broader and complete coverage. There’s cross reactivity between Types I and II,” he notes, comparing that to killed products that until recently, even when used correctly, weren’t providing protection against Type II BVD. There are a couple now that include Type II, he adds.
There’s also “more narrow” immunity offered by killed product. There’s less local immunity and less cellular immunity.
With BVD, there is the headache of the persistently infected (PI) animal, a virus factory threatening her herdmates. The PI is produced in the womb, when exposed to BVD virus in the first 120 days of pregnancy. PIs don’t recognize BVD virus as anything foreign. It’s part of their makeup.
Schultz says even if the perfectly-normal-looking PI is properly vaccinated (or so you think), you can still have reproductive problems in the herd. That’s why it’s important to try and pinpoint the PIs, and cull them - and their offspring.
Schultz says that of the infectious diseases for which dairymen should take biosecurity precautions, BVD can spread the fastest and cause the most problems in the shortest period of time
Ask that incoming cattle be tested for BVD virus (versus antibodies), He warns that a dairyman is “asking for problems if he doesn’t have his herd vaccinated” properly ahead of time, too.
It’s also recommended dairymen buy only animals from herds with a known effective vaccination program. Get specific information about the vaccination history, such as vaccine used. Make sure that primary series was given.
Schultz says he’d definitely reject PIs that turn up from the testing. But what about the others? Farmers need to ask themselves several questions about how risky those herdmates might be. Are the calves of the others going to be PIs? How far bred are they? How long have the non-PIs been with the PIs?
Speaking just to custom heifer rearers, he says the liability of bringing in a PI is “so great” that he thinks the farmers whose calves you’re raising should be required to pay for the virus test. A test for virus can be done at any age, but is must be an anticoagulated test for under three months, while a serum sample is acceptable for over that age.
Farmers selling bred heifers should test and then use it as a marketing tool that it’s non-PI animals they’re offering.
Testing is cheap insurance - $5 a head, with a lot of peace of mind.
Finally he says, “Regardless of the value of a PI animal, don’t sell it to your neighbor.” He knows of a famous PI animal, whose daughters and sons went all over the country.
Another place Schultz says farmers trip up in their vaccinations is not properly handling the vaccine itself, and thereby reducing its efficacy.
On a hot summer day, he recommends vaccines should be kept on ice and kept cold. Once you’re reconstituted a vaccine, you can’t refreeze it. And you shouldn’t refrigerate reconstituted vaccine for more than three days.
Dirty needles in and out of the vial of vaccine are another no-no. Even if the vaccine is only kept in the refrigerator for three days, there can be enough bacterial contamination during that time to destroy the virus.
Finally, he advises farmers to steer clear of “feed store vaccinations,” which he says generally aren’t as good as the vaccines vets carry. There is a difference between vaccines - a range in product quality.
As for farmers who don’t vaccinate for BVD at all and have no problems to date. That, says Schultz, “just means they’re lucky.”
Reprinted with permission from
AGRI-VIEW, March 19, 1998.
Written by Jane Fyksen