Results
A total of 52 horses fulfilled the initial inclusion criteria. Four were excluded due to incomplete FEC data, leaving 48 horses that completed the study. These 48 horses were kept at 17 different premises, including 9 horses at private yards, 35 at livery yards and 4 at racing yards. Age was recorded in 46 horses (mean age 11.8 years; range 1 – 26 years). Breeds were recorded in 44 horses (15 ponies, 8 Thoroughbreds, 8 warmbloods, 8 sports horses, 4 cobs and 1 draught horse). There were 17 mares and 31 geldings. The mean number of horses grazing on the same pasture as the faecal sampled horses was 3 (range 1 – 11) (stocking rate was not recorded). Pasture hygiene (retrieval of faeces from the pasture, “poo-picking”) was routinely performed on 29 of the premises (including 15 where the owners reported “regularly doing this daily”, 8 where this was done “2-3 times a week”, one where this was done “weekly”, and 7 where this was done “irregularly in combination with harrowing”). The horses grazed, on average, 15 hours per day (range 2 – 24 hours) during the study period (August 2017-March 2018).
The mean FEC prior to treatment was 1047 EPG (range 375 – 2137). The numbers of horses with positive FECs and numbers of horses with FEC reduction <90% compared to the pre-moxidectin treatment FEC at the different time poits are shown in Figure 1. Two horses had a positive FEC 2 weeks after dosing with moxidectin; both had a FEC of 12.5 EPG, which represented reductions of 97.8% and 98.3% compared to the mean pre-treatment FEC. All other horses had a 0 FEC at 2 weeks. At 4 weeks post-treatment, 6 horses had positive FECs representing percentage reductions compared to the pre-treatment FEC (i.e., faecal egg count reduction (FECR)) of between 96.6% and 99.2%. At 6 weeks post-treatment, 11 horses had positive FECs; one of these had a FECR of 83.8%, whilst the others were all >90%. At 8 weeks, 21 horses had positive FECs; 2 of these had a FECR of <90% (73.2% and 83.8%), whilst the others were all >90%. At 10 weeks, 27 horses had positive FECs; 6 of these had a FECR of <90% (50.0% to 89.6%), whilst the others demonstrated FECRs >90%. At 12 weeks, 31 horses had positive FECs; 11 of these had a FECR of <90% (range 55.7% to 89.6%), whilst the others were all >90%. At 14 weeks, 34 horses had positive FECs; 13 of these horses had a FECR of <90% (range 50.0% to 89.6%), whilst the others were all >90%. At 16 weeks, 38 horses had positive FECs; 17 of these horses had a FECR of <90% (range 50.0% to 89.6%), whilst the others were all >90%.