Tuesday, October 1, 2013

Levamisole and Moxidectin Effective

Last year was the first year that sheep were grazed at the test site. The purpose of sheep grazing is to help manage surplus forage, as well as contaminate the pastures with infective worm larvae. The sheep (usually mature ewes) are grazed in the spring prior to the test and in the fall after the test.

In 2014, untreated sheep will be brought in to graze the cool season paddocks prior to the start of the test in June. Since the test goats are triple-dewormed at the start of the test, the worm eggs deposited by the sheep serve as the primary source of infection for the test goats. For this reason, it is important to know which dewormers are effective in the sheep that are grazing and contaminating the test pastures.

Untreated sheep are used to contaminate the paddocks.

A DrenchRite® test was conducted to determine the efficacy of the different dewormers. On October 4, a pooled fecal sample was collected from the farm that provides sheep for grazing. The sample contained 2,050 epg. It was composed of 96 percent Haemonchus contortus, 3 percent Trichostrongylus /Teladorsagia mix, and 1 percent Oesophagostumum. There were also several strongyloides present in both the fecal and larvae.

According to the results of the DrenchRite® test, the benzimidazoles and ivermectins are not effective on the worms from this farm. Benzimidazoles include Fenbendazole (SafeGuard®) and Albendazole (Valbazen®). The ivermectins include Ivomec®, Eprinex®, and Dectomax®.

The worms are susceptible to levamisole (Prohibit®) and moxidectin (Cydectin®).  The DrenchRite test does not determine Cydectin resistance directly; it is estimated based on the results for ivermectin. Moxidectin and ivermectin are in the same drug class (Macrocylic Lactones), but are in different sub-groups, acting on a different neurological chemical.

This is good news for the goat test. It means that levamisole and Cydectin will continue to be effective treatments for parasitized goats. The results of this single DrenchRite® test (for a farm in Maryland) are fairly typical of the industry as a whole. While resistance can vary from farm to farm, the dewormers with the most resistance tend to be benzimidazoles and ivermectins. Levamisole and moxidectin tend to be more effective on most farms. 

To determine drug efficacy on your farm, you need to do fecal egg count reduction tests or have a DrenchRite® test done. Without this knowledge, you can't effectively manage parasites on your farm. Dr. Ray Kaplan's lab at the University of Georgia is the only lab (in the U.S.) that performs the DrenchRite® test. For information contact the lab at (706) 542-0742, jscb@uga.edu, or bstorey@uga.edu. You can perform your own fecal egg count reduction tests.

Read more about the DrenchRite® Assay
Learn how to do your own fecal egg counts