Does fluralaner (Exzolt® 5%) affect the enzootic stability of tick fever in beef calves subjected to strategic tick control in a tropical region?

Abstract

Background Little is known about the impact of fluralaner on herd enzootic stability regarding tick fever pathogens (TFPs). This study aimed to assess whether implementing strategic control of Rhipicephalus microplus using fluralaner could influence the enzootic stability of beef herds regarding TFPs on a farm where this compound had never been previously used.

Methods One hundred Bos taurus indicus calves were divided into two groups of 50 animals each. One group underwent strategic tick control with pour-on fluralaner at 2.5 mg/kg (FLU), while the control group received a pour-on combination of fipronil 1.25 mg/kg + fluazuron 2.5 mg/kg (FIFLUA), a protocol used on the farm for 12 years. Calves were monitored from 25 to 241 days of age (weaning). During this period, in addition to acaricide treatments, tick counts and TFP diagnosis via indirect enzyme-linked immunosorbent assay (iELISA), quantitative polymerase chain reaction (qPCR), and blood smears were conducted in both groups.

Results FIFLUA animals received four acaricide treatments at 25, 60, 135, and 188 days of age, with intervals of 35, 75, and 53 days. FLU animals received three acaricide treatments, at 25, 135, and 188 days of age, with intervals of 110 and 53 days. The average tick count in the FLU group was significantly lower than in the FIFLUA group at 60 days (Kruskal–Wallis, H = 97.85, df = 1, P < 0.0001) and 241 days (H = 18.12, df = 1, P < 0.0001). Anaplasma marginale bacteremia was lower in the FLU group at 60 days (H = 3.98, df = 1, P = 0.0459). Serologically, enzootic stability for Babesia bovis was achieved at 135 and 188 days in the FLU and FIFLUA groups, respectively. For B. bigemina, over 75% of calves in both groups showed antibodies at 60 and 188 days, respectively. For A. marginale, enzootic stability was reached at 188 days (FLU) and 241 days (FIFLUA).

Conclusions Strategic tick control with fluralaner did not compromise the development of enzootic stability to B. bovis, B. bigemina, and A. marginale. Over 75% of FLU-treated calves showed seroconversion at 133, 60, and 188 days, respectively.