COMPARISON OF MOXIDECTIN ORAL GEL AND IVERMECTIN ORAL PASTE AGAINST ASPECTRUM OF INTERNAL PARASITES OF PONIES WITH SPECIAL ATTENTION TO ENCYSTED CYATHOSTOME LARVAE

Two dosages of moxidectin oral gel were evaluated and compared to a th erapeutic dose of ivermectin oral paste in the control of a spectrum o f gastrointestinal parasites of ponies naturally infected in southern Louisiana or Mississippi. Thirty-two mixed-breed ponies ranging in age from one to 21 years were used in this controlled test. Eight weeks p rior to the experiment, ponies grazing on contaminated pasture were mo ved to a paddock and fed a pelleted ration, thus reducing or eliminati ng the potential for additional infection and ensuring the existence o f a population of encysted larvae. Ponies were then allocated to repli cates of four animals based on values of fecal strongyle egg counts an d percent strongyle larvae composition determined from Baermann sedime ntations of fecal cultures. Members of replicates were allocated to on e of four treatment groups: moxidectin oral gel administered at 300 mu g kg(-1) body weight, moxidectin oral gel at 400 mu g kg(-1), the ora l gel vehicle as negative control, and ivermectin oral paste at 200 mu g kg(-1). Prior to treatment, ponies were confined in pairs to covere d concrete runs by treatment group. Two weeks following treatment, nec ropsy examinations of all animals were performed. Parasites were recov ered from the lumen of the stomach, the intestinal tract, the cranial mesenteric artery and its major branches, the peritoneal body wall and from pepsin digests of mucosal scrapings taken from the cecum and lar ge colon. Encysted cyathostome larval burdens were also compared using mural transillumination of segments of the large colon for visualizat ion of the encysted forms. Control ponies were not uniformly infected with the spectrum of parasites; however, moxidectin, at either dosage, compared favorably with ivermectin in the control of the adults of St rongylus vulgaris, Stronpylus edentatus, Triodontophorus spp., Oesopha godontus robustus, Trichostrongylus axei, Oxyuris equi, Parascaris equ orum, Habronema muscae, as well as both the adult and larval Cyathosto minae recovered from the lumen. Moxidectin also appears as efficacious as ivermectin against migrating large strongyle larvae at the two wee ks post-treatment evaluation. Moxidectin demonstrated a trend towards greater efficacy against encysted cyathostome larvae than a therapeuti c dosage of ivermectin, but this difference was not statistically sign ificant. Moxidectin was less effective than ivermectin against Gastero philus intestinalis and was equally ineffective as ivermectin against Anoplocephala perfoliata.