Based on early results across 200,000 head of cattle, a new approach to bovine viral diarrhea virus (BVDV) vaccination is halving the treatments and re-pulls in feedlots. Thoughts are that stocker operators can also benefit.
In a nutshell, Scott Crain, DVM, who owns Cattle Health Management Network (CHMN) – a veterinary consulting service for feedyards – was as frustrated with late-day pulls as his clients were. He discovered BVDV 1b present in many of those situations.
"We know that we have BVDV 1b making cattle sick at all stages of the cattle-feeding period," Crain says. "We know we have that happening with cattle vaccinated multiple times for the BVDV 1a and 2a available in commercial vaccines."
This particular strain of BVDV is nothing new. By last year, 1b was the predominant BVDV strain isolated in cattle persistently infected (PI) with BVDV entering two feedlots in Kansas (78.3%) and Oklahoma (64.8%). That’s according to a multi-year study conducted by the Agricultural Research Service (ARS). But commercial vaccines don’t currently contain the 1b strain.
Fast forward, CHMN and a group of other like-minded veterinarians formed Professional Veterinary Associates (PVA) – representing about 5 million head of fed cattle – to utilize a diagnostic process called antigenic cartography.
This process involves mapping the genes of the virus strains then comparing them to strains in the vaccines available. Specifically scientists look at differences between antigens, which induce antibody production that can produce an immune response to the virus. That tells researchers whether a current vaccine protects against other strains and subtypes, or how much of the new pathogen can escape the immune response generated by viral antigens contained in the current vaccine.
In the simplest terms, PVA developed a protocol that begins with participating veterinarians collecting and submitting BVDV samples to a national virus data bank.
The veterinarians map the genes of submitted samples and compare them to strains of the BVDV virus in vaccines they’re using. If they encounter a strain or subtype that's escaping immune response, such as 1b, they build an autogenous (custom-made) vaccine containing the specific strains or subtypes they’re isolating.
Though commonplace in the swine industry, autogenous vaccines have a shadowy past in the cattle business where they’ve often been equated to bathtub mixes or outright snake oil.
"You must have the right antigens in the autogenous product to be effective," explains Nate McDonald, CHMN managing director. "The key to getting the right antigens in an autogenous product is the antigenic cartography process, coupled with a surveillance program that continuously identifies the pathogens currently causing disease in the field."
Crain emphasizes, this approach is intended to supplement commercial BVDV vaccines, not to replace them. One reason 1b is currently the predominant subtype found in cattle infected with BVDV is because commercial vaccines contain the known BVDV genotypes 1a and 2a.
By law, autogenous vaccines can only contain killed strains of a virus. According to McDonald, modified-live vaccines prompt a faster immune response.
See more details in the September issue of BEEF magazine.