Impact on beef cattle productivity of infection with anthelmintic-resistant nematodes

CANTON, C; CEBALLOS, L; DOMÍNGUEZ, MP; FIEL, C; LIRÓN, JP; MORENO, L; CANTON, L; BERNAT, G; LANUSSE, C; ALVAREZ, LI

NEW ZEALAND VETERINARY JOURNAL

NEW ZEALAND VETERINARY ASSOC INC

Lugar: Londres; Año: 2019 vol. 68 p. 187 - 192

0048-0169

AIMS: The main goal of the current study was to evaluate, on a commercial beef cattle farm, theimpact of infection with gastrointestinal nematodes resistant to both ivermectin (IVM) andmoxidectin (MXD) on the productivity of calves.METHODS: Male Aberdeen Angus calves, aged 9?11 months, with faecal nematode egg counts(FEC) ≥200 epg and body weight ≥190 kg, were allocated to two herds. Herd A (n=90) grazed awinter forage crop rotation of maize and Herd B (n=90) grazed a 2-year-old Agropyrum pasture. OnDay 0 in each herd, calves were randomly allocated into five groups (n=18), which were treatedwith 0.2 mg/kg IVM; 0.2 mg/kg MXD; 3.75 mg/kg ricobendazole (RBZ), both IVM and RBZ, orremained untreated. Faecal samples collected on Days −1 and 19 were used to determine thepercentage reduction in FEC, and genera of the nematodes were determined by the identification ofthe third-stage larvae recovered from faecal cultures. Total weight gain was determined from bodyweights recorded on Days −1 and 91.RESULTS: Overall mean reduction in FEC was 42% for IVM, 67% for MXD, 97% for RBZ and99% for IVM + RBZ. The reduction in FEC for Cooperia spp. was ≤78% for IVM and MXD, andfor Haemonchus spp. was 0 and 36% for IVM and MXD, respectively, confirming the presence ofparasites resistant to both anthelmintics. Only IVM + RBZ treatment resulted in 100% efficacyagainst Haemonchus spp. The overall estimated mean total weight gain for calves treated with IVMwas 15.7 (95% CI=11.9?19.7) kg and for calves treated with IVM + RBZ was 28.8 (95% CI= 25?32.5) kg (p