As many producers may be aware, cattle deworming can offer numerous benefits in terms of herd health and operational costs. But accompanying any parasite-control strategy is the complicated issue of resistance, which occurs when a parasite population begins to survive treatment from a drug that at one time was effective. Due to the number of internal and external parasite species found in cattle, resistance is nearly impossible to stop completely. But by learning how resistance affects herd health, producers can treat their cattle and make the most of their deworming efforts.
When an animal is treated with any dewormer, there are two opportunities of selection for resistance: at the head and at the tail.
Head selection can happen when parasites survive the drug’s initial peak. According to Dr. Tony Moravec, DVM, Merial Large Animal Veterinary Services, a common cause can be treating to the average weight of the herd, which could mean under-dosing a significant portion of the cattle. Inaccurate weight estimates can also cause head selection for resistance, he says, which is why using a scale is so important.
Tail selection occurs primarily when the drug drops below therapeutic levels before it exits an animal's body. If small amounts of the drug linger for a long period of time, various parasites are exposed to the drug. The susceptible exposed worms die at this sub-therapeutic level, eliminating those susceptible genes from the gene pool.
With each successive treatment, a growing percentage of parasites may survive, passing on their resistant genes to the next generation as they breed and multiply, Moravec says. As treatments continue, the newly resistant parasites begin to outnumber those still vulnerable to the dewormer, rendering the treatments ineffective.
Because resistance occurs over time and through multiple treatments, some question the efficacy of extended-release dewormers in combatting resistant parasites. But there’s another side to that story.
LONGRANGE® (eprinomectin) is the first extended-release dewormer that provides up to 100 to 150 days of parasite control in a single treatment. The extended duration of activity is provided by the unique THERAPHASE™ formulation, which allows for a gradual release of eprinomectin with two peaks.
“LONGRANGE may be a major product breakthrough in helping to battle resistance,” Moravec says. “The reason is the THERAPHASE formulation, which systematically delivers the active ingredient into the animal’s system, as opposed to using the animal’s fat cells as a reservoir.”
Long-acting deworming products have shown to be effective against stubborn parasites, including Cooperia spp., because they provide either a high initial peak or a large area under the curve, or drug exposure time. LONGRANGE is proven to provide both the high initial peak and a large area under the curve, helping it fight parasites that might otherwise survive at lower-dose exposures of conventional pour-ons and injections.
As a comparison, the initial peak achieved by LONGRANGE is roughly two and a half times that of EPRINEX (eprinomectin), the conventional pour-on dewormer that provides the broadest-spectrum of parasite control available. This high initial peak can help combat head selection for resistance. In addition, the unique THERAPHASE formulation found in LONGRANGE delivers a second peak of eprinomectin 90 to 100 days after the initial injection. This creates an area under the curve that is about five times greater than that of EPRINEX.
While the second peak dosage runs its course, the THERAPHASE formulation allows LONGRANGE to exit the animal’s system quickly. The short amount of time at sub-therapeutic concentrations, or the tail, helps ensure that there is minimal selection for resistance.
“What people tend to worry about with extended-release products is the lingering residual effect,” Moravec says. “But that’s where the THERAPHASE formulation comes into play. Since eprinomectin is delivered with the THERAPHASE matrix and is not bound by fat in the tissues, it can spend more time battling the parasites and then get out of the animal’s system.”
Without THERAPHASE, most conventional pour-ons and injections only last for a few days to a few weeks before pasture reinfection begins. Multiple treatments could be needed to curb the reinfestation. But because LONGRANGE offers up to 100 to 150 days of parasite control with just one subcutaneous injection, multiple treatment frequencies are not an issue. One treatment per fall and spring season means there will be minimal selection for resistance, decreasing the opportunity for parasites to resist the drug.
While long-acting dewormers’ association with parasite resistance may be a subject of question among producers, LONGRANGE is no more likely to drive resistance than a single dose of conventional dewormers. LONGRANGE is available through a prescription from a veterinarian.
For more information, visit theLONGRANGElook.com.