The study determined the resistance of ivermectin in cattle tick Rhipicephalus microplus from selected slaughterhouses in Nueva Vizcaya by larval packet test. The study included 4 Treatment concentrations. Treatment 1 (negative control), Treatment 2 (0.5% ivermectin concentration), Treatment 3 (0.746% ivermectin concentration) and Treatment 4 (0.898% ivermectin concentration) Based on the result of the study, larvae in the treatment 4 exposed at 0898% ivermectin concentration showed susceptibility with restriction to ivermectin It is significantly different from the rest of the treatments. The larvae in the Treatment 3 with 0.746% ivermectin concentration predominantly showed emerging resistance to ivermectin, three of the municipalities (Aritao, Bambang. Bayombong) resulted emerging resistance to ivermectin while one municipality (Kasıbu) showed susceptibility with restriction to ivermectin Three of the municipalities in treatment 2 with the larvae exposed at 05% ivermectin concentration showed resistance (Aritao, Bambang, Bayombong) and one municipality (Kasibu) showed emerging resistance to ivermectin. Treatment I with 0% ivermectin concentration (negative control) indicated absence of deaths from the larvae due to the absence of ivermectin concentration impregnated in the paper packets. As the concentration of ivermectin increases, the percentage mortality is also increased In Kasibu, resistance was not seen in any level of the ivermectin concentrations, thus ivermectin is still highly effectively, and can still be used as an effective means in controlling the larvae of Rhipicephalus microplus. While, in the municipalities of Aritao, Bambang and Bayombong showed resistance to ivermectin at low concentration and susceptibility to ivermectin at higher concentrations. Therefore, new means of eradicating larvae of Rhipicephalus microphus is recommended.

Thesis (Doctor of Veterinary Medicine)

includes appendices and bibliographical references.