We evaluated the efficacy and residual load of an antiparasitic oral in gel (doraQuestl.a. ?) based on doramectina composition is 1.75% (w/w) in riding horses, for the control of gastrointestinal nematodiasis, for a period of 70 days post- treatment. The study was conducted at the Army Equitation School of La Molina, Lima, Peru, between the months of January to March 2007. Twenty horses were selected, whose ages were an average of 5 years, naturally infected with gastrointestinal parasites and parasitic load egg type Strongylus older than 200 HPG. The horses were distributed equally according to their parasite load, into two groups, control (untreated), and another group treated with doraQuest l.a. ?, by oral. Dosage used was 200 mcg / kg. All animals remained together during the period of the experiment. The results showed that(doraQuest L.a.?) by the oral route showed a high efficiency 100%, against strongylus eggs, from 7 up to 63 days after treatment and was effective until the day 70, time that lasted for the evaluation against gastrointestinal nematodes. With the proof of the found results in horses, doraQuest l.a. ?, prevents the re-infection of nematodes, for a periodof approximately 60 days, because from the 70 days the presence of type strongylus eggs was observed. There were no adverse reactions when accomplishing the dosification in horses.