By JORDAN STRICKLER

Kentucky Correspondent

MANHATTAN, Kan. — Kansas State University has been awarded two $250,000 grants by the U.S. Food and Drug Administration (FDA) to help target and define durations of use for certain medically important antimicrobial drugs approved for use in the feed of food-producing animals.

Defining targeted durations of use is one component of the FDA’s five-year plan, Supporting Antimicrobial Stewardship in Veterinary Settings, published in September 2018, that outlines key goals and objectives for fiscal years 2019-23.

This plan applies a risk-based approach to antimicrobial resistance and supports the FDA's ongoing efforts to slow its development by fostering the judicious use of medically important antimicrobial drugs (those important in human medicine) in animals.

In 2017, the FDA completed the implementation of Guidance for Industry #213, a process begun in 2013 to transition medically important antimicrobials that are used in the feed or drinking water of food-producing animals to veterinary oversight, and eliminate the use of these products in animals for production (e.g., growth promotion) purposes.

According to the FDA, there are approximately 11 individual products and in excess of 30 pioneer combinations of medicated feed which have no current “duration of use” definition. So in April, the FDA announced it would offer proposals to help target and define the duration of use for antimicrobials that are approved for use in livestock feed.

The two projects approved for KSU involve an evaluation of the timing and duration of use for chlortetracycline treatment of bovine anaplasmosis in adult cattle, and defining the targeted durations for use of tylosin phosphate to prevent liver abscess formation in feedlot cattle.

Anaplasmosis is a tick-borne infectious blood disease in cattle also known as yellow bag or yellow fever. Tetracycline is the most common drug used for the illness. The incubation time for the disease to develop generally varies from two weeks to more than three months, with an average of 3-4 weeks.

“The first part of the anaplasmosis study that we are going to do is treat for a defined period of time,” said Dr. Kathryn Reif, assistant professor in KSU’s Department of Diagnostic Medicine/Pathobiology in the College of Veterinary Medicine. “We are then going to stagger that treatment around the point of inoculation; a couple of timelines before infection and a couple of timelines after infection.

“We are looking for that window relative to the point of infection where we need to get treatment on board to prevent an animal from coming down with clinical anaplasmosis.”

Animals will typically display symptoms of anaplasmosis within 30-40 days after infection. Reif explained if researchers can find when that “sweet spot” is, then they can begin to look for an ideal pulsing regimen.

“Obviously, the producer doesn’t know when their animal is going to become infected, so one thing we want to see if they can strategically pulse-treat in order to effectively control anaplasmosis, or is treating that full duration really necessary.”

Reif is also hoping the study will allow them to re-confirm that the current FDA-approved dosages of chloretetracycline are still effective. “That will be a big deal because producers now have to follow the stated directions for the drug with regard to the in-feed antimicrobials,” she said.

“So, it’s really important to verify that what is legal to do is still effective. Also, has the effectiveness changed because the strains have changed? For our study we will be using a strain of the pathogen we isolated from an infected cow in 2018.”

Since the 1960s liver abscesses have been identified as a problem associated with feeding high-concentrate finishing rations to feedlot cattle. The second study will be aiming to find the best targeted durations for use of tylosin phosphate to prevent liver abscess formation in these cattle.

These abscesses, caused by Fusobacterium necrophorum and Arcanobacterium (Actinomyces) pyogenes, can lead to decreased feedlot performance and carcass value. The FDA’s Center for Veterinary Medicine currently recommends 8-10 grams per ton of tylosin phosphate as treatment to significantly reduce the number of liver abscesses and increase feed efficiency.

Depending on available funding and satisfactory progress by the awardees, the FDA may grant an additional year of support of up to $250,000 each for the researchers to continue their studies in FY 2020.