439 - Effect of Anti-acaricide Treatment on Tick Species Present and Performance of Growing Beef Heifers

The Edwards Plateau region of Texas is largely used for grazing cattle and small ruminants. Tick parasitism in range livestock can occur year-round with direct production losses manifested as body weight or condition. The objective was to assess two acaricide treatments on the active tick burden on livestock within two forage growing seasons (winter through summer). At the Sonora AgriLife Station, 22 Bos taurus crossbred heifers (248 ± 47 kg) were maintained on 97 hectares of rangeland. Tick burden was assessed by individual animal inspection every two weeks from 18-Dec-2019 to 11-May-2020 (Season 1) and from 8-Jun-2020 to 3-Aug-2020 (Season 2). Acaricide treatment was applied each date to heifers chosen randomly to serve in the non-treated control (control: 11 heifers) or acaricide-treated (treatment: 11 heifers) groups. Season 1 acaricide treatment was a pour-on synthetic pyrethroid (11 dates) and Season 2 was a diluted synthetic pyrethroid whole-body spray (5 dates). Tick species observed included Amblyomma americanum and Dermacentor albipictus. Tick burden (total counts) and body condition score differences were determined by analysis of variance procedures. For tick burden, there were significant differences (P < 0.0012) between treatment (0.528 ± 0.06) and control (0.819 ± 0.06) heifers in Season 1 (0.673 ± 10.44), and no differences (P > 0.11) between treatment (0.642 ± 0.07) and control (0.799 ± 0.07) heifers in Season 2 (0.721 ± 2.64). For body condition score, there were no differences (P > 0.72) between treatment (5.61 ± 0.04) and control (5.59 ± 0.04) heifers in Season 1 nor Season 2 (5.51 ± 0.005 and 5.80 ± 0.47, respectively). Season 1 acaricide treatment was effective in controlling tick burden (efficacy = 3–4 weeks) as compared to Season 2 (efficacy = 1–2 weeks). Tick burdens observed under the conditions of this study had no effect on body condition.