A good parasite-control program can provide some of the highest economic returns of any management practice available to beef producers, but timing and product selection are critical, and most producers do not consult their veterinarians in their decisions. During the Cattle Industry Convention in Tampa, we visited with Merial technical-services veterinarian Joe Dedrickson, and while the discussion centered around the company’s new “Longrange” extended-release product, much of the focus was on the value of involving a veterinarian in planning your parasite-control program.

Iowa State University research has shown that parasite control can return as much as $201 per head due to better health, improved weight gains and reproductive efficiency. Dedrickson says a good deworming program typically can improve calf weaning weights by 25 pounds – worth close to $50 in today’s market – for a treatment cost of about a penny per pound or $5 for a 500-pound calf.

Longrange (eprinomectrin )is a broad-spectrum injectable dewormer that provides 100 to 150 days of control with a single dose, depending on the parasite species. It also is a prescription product, meaning producers interested in using it will need to involve their veterinarians. Regardless of which products a producer ends up using, that relationship should help ensure proper timing and targeted treatment, resulting in better parasite control, better cattle performance and less risk of parasites developing resistance to dewormers.

Resistance among worm species affecting cattle has not become a widespread problem, but veterinarians and parasitologists have become concerned as some resistant populations have turned up, particularly in the case of Cooperia species of intestinal worms. Resistance to dewormers can occur when a small number of worms survive the treatment and go on to reproduce, passing their genetic ability to resist the product on to their offspring. Over time, a population of resistant worms could develop. Insufficient dosage of a product, resulting in lower efficacy and survival of more worms, could contribute to the development of resistance.

Dedrickson says the Longrange product provides an initial peak of activity at treatment, with some of the dewormer reserved in a gel matrix for later release into the animal’s bloodstream. Levels of the product in the animal’s bloodstream decline somewhat over 100 days following treatment, but remain well above the minimum level for efficacy. A second peak occurs at about 100 days as the gel matrix dissolves and releases more of the active ingredient into the bloodstream. At the end of the treatment period, levels of the product in the animals drops to near zero quickly, within two to eight days, meaning just a short period when dosage levels are below that needed to kill the majority of worms.

Timing is an important consideration in spring deworming. Dedrickson says that in most cases, about 10 percent of the worms on a ranch are in the animals while 90 percent are on the pastures. Worms that overwintered on pastures move up from the ground onto forage plants during March and April in the South — later further north — when temperatures average higher than 50 degrees. Treating too early, before worms become active in pastures, can mean cattle become re-infected soon after treatment, unless the deworming product has residual activity to extend through the infective period. With that in mind, strategic-deworming recommendations typically involve treating in late spring, after cattle have harvested the worms.

Treatment reduces the number of eggs cattle shed onto pastures in their manure, but multiple treatments can be needed to keep cattle from becoming re-infected by worms already present in the pasture. An extended-release product, Dedrickson says, can eliminate the need for multiple treatments and should help break the lifecycle of worms, resulting in cleaner pastures.

In any case, a conversation with your veterinarian can help you plan and implement a program that provides the most cost-effective parasite control over the long term.