Three studies were conducted to confirm the efficacy of the Exzolt dosage regime found effective in previous dose-determination studies (0.5 mg fluralaner/kg BW in drinking water twice at a 7-day interval). The 3 studies, conducted under a common protocol at commercial laying farms of different sizes in Germany, France and Spain, evaluated Exzolt dose efficacy for treating natural infestations of poultry red mites (D. gallinae) (Table 5-1)1.
Unlike the previous dose-determination studies that directly evaluated efficacy by killing mites feeding on treated animals, these dose-confirmation studies assessed the effect of treatment on the reduction of the mite population in the house.
- Three controlled single-site dose-confirmation studies. Each study involved a qualifying commercial laying hen farm (in Germany, France or Spain) with 2 comparable houses naturally infested with poultry red mites (no recent acaricide treatment).
- The 2 houses at each of the 3 enrolled farms were as similar as possible with regard to size, breed, and age of chickens; feed/water distribution systems; and housing system (Table 5-1).
- Mite infestation levels of each house were assessed using mite traps, with farm eligibility confirmed if mite counts averaged > 100 in each house. Field isolates of study mites were confirmed to be susceptible to fluralaner using a contact in vitro test (LC90 < 15.63 ppm).
- On day 0 at each farm, birds in 1 house were treated with Exzolt (0.5 mg/kg BW/day twice 7 days apart) and the remaining house was left untreated (controls). Houses with the highest mite infestations were selected for Exzolt treatment, for animal welfare reasons. Treatment was administered either using a medication tank or a dosing pump.
- Additional mite traps were placed at the same locations on day -1 (baseline infestation level) and at multiple time-points thereafter. Traps were removed after 24 hours for mite differentiation and counting.
- Data were also collected regarding adverse events and the number of dead chickens, laid eggs, and downgraded eggs (study B) per house.
- Personnel involved in the assessment of efficacy and safety criteria were blinded to treatment group assignments.
Efficacy assessment was based on the percentage reduction of mites (mobile stages, i.e., larvae, nymphs, adults) in the treated house at each post treatment time-point compared to the control house. Production parameters were descriptively analysed.
Study A was concluded after 4 months because mite counts decreased spontaneously in the control group. Study B was concluded at the end of the scheduled production cycle of the hens, after about 3 months. Study C extended about 6 months, until regrowth of the mite population in the treated house reached 50% of the baseline count. However, the birds in the control house received treatment with another product at week 11 (day 77) to ensure appropriate animal welfare. Analyses of water samples from all 3 studies confirmed that actual fluralaner concentrations were generally close to target levels.
The efficacy of Exzolt against all mite stages compared to controls is summarized in Figure 5-2. For all studies, efficacy resulting from the complete 2-dose regime exceeded 99% from day 6 onwards, achieving 100% at several time-points. Efficacy remained high through the end of the production cycle in study B (3 months) and for 17 and 19 weeks in studies A and C, respectively.
As expected, Exzolt efficacy against larval non-blood-feeding stages of mites (Figure 5-3) increased more slowly than efficacy against nymphs and/or adults. However, as larval stages progressed to later blood-feeding forms, Exzolt efficacy was more consistently detected, with more than 95% efficacy confirmed by day 6 (before the second administration). Thereafter, mite counts for larvae, nymphs, and adults were similar.
Favourable impacts of effective mite control were also observed for several production parameters (Figure 5-4). For each parameter, the difference between the Exzolt group and controls was calculated pre-treatment (week -1) and post treatment (from first treatment through study conclusion). Mortality remained very low in both houses of each study. Overall, birds treated with Exzolt experienced an increase in the laying rate (0.9-1.9%) and a decrease in the percentage of downgraded eggs in study B (3.4% more normal eggs). These productivity benefits reflect the successful and prolonged relief of ectoparasite burdens by Exzolt, which thus allowed for better productivity in these field studies.
No adverse events related to the use of Exzolt were reported during the studies.
Dose-confirmation studies demonstrated that Exzolt consistently provided high efficacy against poultry red mites when administered at 0.5 mg fluralaner/kg BW given twice 7 days apart via drinking water. Treated birds also demonstrated excellent tolerance of Exzolt, with no treatment-related adverse effects observed. Under commercial production conditions in these studies, the 2-dose Exzolt regime successfully controlled mite infestations for extended periods far exceeding the 2 weeks of effective blood concentrations. This extended period of efficacy was due to the ability of Exzolt to interrupt mite life cycles and, thus, massively decrease mite populations of the houses.
- Data on file. MSD Animal Health.