DOSE TITRATION OF MOXIDECTIN ORAL GEL AGAINST MIGRATING STRONGYLUS-VULGARIS AND PARASCARIS-EQUORUM LARVAE IN PONY FOALS

Moxidectin was tested for efficacy in ponies against experimental infe ctions of 56 day Strongylus vulgaris larvae and 11 day Parascaris equo rum larvae. Three dosages of moxidectin were tested: 300 mu g per kg l ive body weight, 400 mu g per kg, and 500 mu g per kg, and the vehicle served as control. Ponies were first infected with 600 S. vulgaris th ird-stage larvae (L(3)) on Experiment Day 0 and then with 3000 embryon ated P. equorum eggs on Day 45. Moxidectin treatments were administere d on Day 56 and necropsy examinations were performed on Day 91. Strong ylus vulgaris fourth-stage (L(4)) and fifth-stage (L(5)) larvae were r ecovered at necropsy from the control ponies, in dissections of the cr anial mesenteric artery and its branches (L(4) and L(5)), and recovere d from nodules in the wall of the cecum and ventral colon (L(5)). Para scaris equorum larvae were recovered from the small intestine of contr ol ponies, Moxidectin was highly efficacious against S. vulgaris L(4) and L(5) at all three doses tested (99.6-100%), and appeared to be equ ally efficacious against P. equorum larvae (100%); however, control po nies had low levels of P. equorum infections compared to previous expe rimental infections performed using identical methods, This suggests t hat the prior S. vulgaris infection on Day 0 may have influenced the s ubsequent experimental P. equorum infection on Day 45 and contributed to the lower recovery.