The Veterinary Feed Directive (VFD) was implemented by the Food and Drug Administration (FDA) as one way for the agency to increase its regulatory oversight of the administration of feed-grade antimicrobials, says Harry Snelson, DVM, director of communications for the American Association of Swine Veterinarians (AASV).

The VFD was implemented in 2001 as a result of the enactment of the Animal Drug Availability Act, stemming from a request to approve Elanco’s Pulmotil (tilmicosin) as an aid in the control of respiratory disease.

“We needed something in between a prescription and an over-the-counter category, but still having veterinarian oversight. VFD provided an opportunity for drug companies to continue to get feed-grade antimicrobials approved,” says Tom Burkgren, DVM, executive director of the AASV. The other product approved was Nuflor (florfenicol) from Intervet/Schering-Plough Animal Health.

In its comments to the FDA, the AASV explains that the VFD “serves as a third option for regulating the distribution of animal drugs along with over-the-counter and prescription. The intent was to define a process by which feed-grade drugs can be administered in animal feeds under a veterinarian’s order and professional supervision,” Snelson relates.

The FDA closed the comment period on its proposed rule.
Snelson says the VFD process has worked fairly well, but the process has been somewhat cumbersome.

“AASV supports the judicious use of antimicrobials and believes veterinarians should be involved in the decision-making process for antimicrobial use in animals,” he says.
The AASV addressed a number of issues that could be altered in the VFD process:
• Allowing for electronic submission of forms;
• Providing changes in antimicrobial use calculations;
• Standardizing the VFD form; and
• Shortening document retention requirements to one year.

Regarding changes in calculations for feed additives, Burkgren says the VFD process should provide for “treating the pig rather than treating the feed — calculating milligrams per pound of bodyweight of pigs, not so many grams per ton of feed.” That way, the proper amount of medicated feed can be provided as the pig grows.

Followup Information on Porcine Circovirus Vaccine Efficacy

The article, “Circovirus Presents Environmental Challenge” in the July 15, 2010 issue of National Hog Farmer, discussed research at Kansas State University (KSU) that investigated the role of environmental contaminants in maintaining porcine circovirus in a Kansas hog operation.

The article also pointed out in the affected production system that pigs were being vaccinated with the two-dose porcine circovirus type 2 (PCV2) vaccine (Circumvent PCV, Intervet/Schering-Plough Animal Health), in accordance with label directions for first-dose-administration timing. In the farm described in the environmental PCV2 detection research, this first PCV2 vaccine dose was being administered after pigs had been placed in and exposed to the nursery environment.

In addition to the environmental work, a team of researchers from Intervet/Schering-Plough determined that pigs were viremic (infection of the bloodstream) prior to vaccination, and that by altering the timing of vaccination, the clinical disease problem was eliminated.

“The problem was early exposure to virulent virus prior to vaccination that was subsequently overcome by methodological adjustments to vaccination timing,” explains Charles Francisco, DVM, director of Swine Technical Service, Intervet/Schering-Plough Animal Health.

As the article mentioned, placing pigs in facilities with environmental contamination of porcine circovirus type 2 (PCV2) virus, which have yet to be immunized against PCV2, may affect the efficacy of vaccine if the virus present in the environment is infectious, says KSU swine researcher Megan Potter, DVM.

Applying information obtained from investigative efforts by the affected producers and farm employees, herd veterinarians, and Intervet/Schering-Plough technical services with the environmental PCV2 monitoring data gathered by KSU researchers, it was determined that two-dose vaccination with Circumvent PCV at the proper intervals resulted in an excellent response, minimizing viremia and essentially eliminating circovirus mortality.