Anthelmintic resistance in cattle: A systematic review and meta-analysis

A systematic review and meta-analysis was conducted to identify, evaluate, and synthesize primary literature reporting the efficacy of anthelmintic drugs in cattle. Information on the bibliographic data, anthelmintic drugs, animals, reduction method, days after application, parasite genera, type of application, and dosage were collected. The final data base was composed of 70 articles published between 1986 and 2016 with a total of 8,976 animals. The mode of application interfered with the efficacy of anthelmintic drugs in cattle (P < 0.05); oral application was superior to injectable and pour-on drugs. The combined use of drugs was superior to single macrocyclic lactones including ivermectin (P < 0.05), in this way the combined use was more effective than the single use of drugs for the control of gastro-intestinal nematodes in cattle (P < 0.05). Nematode genera in the abomasum (Ostertagia spp., Haemonchus spp.) and intestine (Cooperia spp.) were evaluated. Levamisole had a greater efficacy for Cooperia spp. than Ostertagia spp. (P < 0.05); ivermectin had a greater efficacy for Ostertagia spp. than Haemonchus spp. (P < 0.05); doramectin had a greater efficacy for Ostertagia spp. than Cooperia spp. (P < 0.05). Dosing in larger quantities and according to the manufacturer's recommendation was most efficient, and the dose limiting species differed between substance classes. The test based on the count of eggs per gram of faeces indicated a reduced efficacy of the drug as days passed following treatment. The forest plot did not show a difference (P > 0.05) between interventions (resistance and efficacy). The results of this systematic review and meta-analysis suggest that anthelmintic resistance in cattle is present on several continents. Therefore, there is a need to replace the schemes based on the exclusive use of drugs in order to decrease the selection pressure.