First evaluation of the efficacy and operational cost of acaricidal bath combining different droplet sizes, pressures and spray patterns in dairy cows naturally infested with Rhipicephalus microplus.

Rhipicephalus microplus poses a significant challenge to animal health. This study evaluated efficacy and the effective operational cost (EOC) of different acaricidal treatments varying droplet size, pressure and spray pattern using a power sprayer. Three experiments were conducted on dairy cows, with each experiment involving three groups of 10 animals: two treated groups and one untreated control group. In the first experiment, acaricide treatments with the same droplet size (medium) were compared at different pressures (50 and 100 psi) using a full cone spray pattern: E1-M50 and E1-M100. In the second experiment, different droplet sizes (fine and medium) were compared at the same pressure (100 psi) using a full cone spray pattern: E2-F100 and E2-M100. The third experiment compared droplet sizes and spray patterns (fine at full cone and ultra coarse at flat fan) at the same pressure (100 psi): E3-F100 and E3-UC100. All animals received acaricide treatment on day 0 with a product based on organophosphate and pyrethroid. Tick counts were performed on days + 7, + 14, and + 21 to determine treatment effectiveness. Data on bath time were collected to determine the EOC, besides cost with acaricide, labor, water and electricity. No statistical differences (p > 0.05) regarding the mean tick count were observed between treated groups in all experiments. However, the highest efficacy values were found in treatments with larger droplets (medium and ultra coarse) and higher pressure (100 psi). In experiment 1, the efficacy varied from 70.6 to 88.9% and 75.2 to 93.7% for the treated groups E1-M50 and E1-M100, respectively. In experiment 2, efficacy varied from 48.7 to 86.2% for E2-F100 and from 68 to 94.7% for E2-M100. In experiment 3, efficacy ranged from 62.9 to 76.9% for E3-F100 and from 73.4 to 86.5% for E3-UC100. The EOC of the acaricide bath varied between 0.42 and 0.46 USD per animal. The findings show that treatment efficacy and EOC vary depending on the spray parameters used for the control of R. microplus, but further studies should be conducted to determine better combinations of pressure, droplet size and spray pattern.