Therapeutic equivalence of ivermectin 1% and two novel formulations combined of ivermectin 1% + fluazuron 12.5% for the control of Rhipicephalus (Boophilus) microplus in beef cattle from Uruguay

Background: Novel combinations of ivermectin and fluazuron are presented as an alternative for control of tick in cattle. Applying combination of drugs with the aim to affect different stages of the parasite´s life cycle is established as a potential measure to achieve control of ticks in cattle. Aim: To determine therapeutic equivalence between two novel formulations of ivermectin 1% combined with fluazuron 12.5% tested on bovines naturally infested with Rhipicephalus (Boophilus) microplus. Methods: Forty adult beef cattle were randomized into four groups (n = 10): IVM [ivermectin 1% (0.2 mg/kg)] and combinations groups A and B [ivermectin 1% (0.2 mg/kg) + fluazuron 12.5% (2.5 mg/kg), each] and Control [untreated]). On days 14, 27 and 49 after administration, the presence of ticks was ranked as null, low, medium and high; a cumulative link model was adjusted to evaluate treatment response. Results: Although all groups had some animals with presence of ticks until day 27, on day 14 IVM (OR 0.013, CI95%: 0.001 to 0.014, p<0.01), A (OR 0.01, CI95%: 0.00 to 0.07, p < 0.01) and B (OR 0.01, CI95%: 0.00 to 0.148, p < 0.01) groups were different when compared to the Control group, unlike on day 27 where only groups A (OR 0.02, CI95%: 0.00 to 0.17, p<0.01) and B (OR 0.06, CI95%: 0.00 to 0.46, p<0.01) remained different from the Control group. On day 49 post-administration IVM and B did not differ from Control group, with 0.95 probability (CI95% 0.92-1.02) of high parasite burden. At day 49 post-administration, Group A was the only group free of ticks (OR 0.01, CI95%: 0.00 to 0.13, p