• Anthelmintic resistance among gastrointestinal nematodes of cattle on dairy calf to beef farms in Ireland

      Kelleher, Anne C; Good, Barbara; de Waal, Theo; Keane, Orla M; Teagasc Walsh Fellowship Programme (Biomed Central, 2020-07-01)
      Background The control of gastrointestinal nematodes (GIN) of cattle in pasture-based production systems such as Ireland is highly dependent on the availability of efficacious anthelmintics. There is very little information available on the efficacy of the broad-spectrum anthelmintics against GIN of cattle in Ireland and the aim of this study was to determine the prevalence of anthelmintic resistance on dairy calf to beef farms. Results GIN burden was monitored on thirty-six recruited farms by performing herd level faecal egg counts (FEC) every 2 weeks. Of these, nine farms were lost from the study as calves were treated with an anthelmintic for Dictyocaulus viviparus, two were lost as they treated for GIN, one dropped out of the study and on one the herd FEC did not reach the threshold for carrying out the Faecal Egg Count Reduction Test (FECRT). On the remaining 23 farms, once the herd FEC reached 100 eggs per gram, a FECRT was carried out. Pre and post-treatment larval cultures were also performed to identify the GIN to genus level. The efficacy of fenbendazole, levamisole, ivermectin and moxidectin was evaluated on 15, 11, 16 and 11 farms respectively. Resistance to fenbendazole was identified on 9 farms (60%) with resistance suspected on a further farm. Resistance to levamisole, ivermectin and moxidectin was detected on 2 (18%), 16 (100%) and 8 (73%) farms respectively. The predominant genera detected pre and post-treatment were Cooperia and Ostertagia with both genera detected post-treatment with fenbendazole and ivermectin. Due to the low proportion of Ostertagia spp. pre-treatment, the efficacy of levamisole or moxidectin against this genus could not be reliably established. Conclusions Anthelmintic resistance was widespread on the sampled dairy calf to beef farms in Ireland with resistance to benzimidazole, levamisole, ivermectin and moxidectin detected.
    • Nematode control in suckler beef cattle over their first two grazing seasons using a targeted selective treatment approach

      O'Shaughnessy, James; Earley, Bernadette; Mee, John F; Doherty, Michael L.; Crosson, Paul; Barrett, Damien; de Waal, Theo; Teagasc Walsh Fellowship Programme (Biomed Central, 2015-06-18)
      Background With concerns over the development of anthelmintic resistance in cattle nematode populations, we must re-examine our approach to nematode control in cattle. Targeted selective treatments (TST), whereby individual animals are treated instead of entire groups, are being investigated as an alternative. The study objective was to determine if anthelmintic usage could be reduced using a TST-based approach to nematode control in spring-born suckler beef cattle over their first and second grazing seasons (SGS) without affecting performance. In the first grazing season (FGS), 99 calves with an initial mean (s.d.) calf age and live weight on day 0 (June 28th 2012) of 107 (23.1) days and 160 (32.5) kg, respectively, were used. The study commenced on day 0 when calves were randomised and allocated to one of two treatments; 1), standard treatment (control) and 2), TST. Control calves were treated subcutaneously with ivermectin on days 0, 41 and 82 in the FGS. All calves were treated with ivermectin on day 124 and housed on day 133. In the SGS, only heifer calves from the FGS were used and control heifers were treated with ivermectin on day 393. Animals were weighed, blood and faecal sampled every three weeks. The TST animals were treated with ivermectin if thresholds based on a combination of plasma pepsinogen concentrations, faecal egg count and/or the presence of Dictyocaulus viviparus larvae in faeces (FGS only) were reached. Results No TST calves reached the treatment threshold criteria in the FGS. The FGS average daily live weight gain (ADG ± s.e.m.) for control and TST group calves was 0.89 ± 0.02 kg and 0.94 ± 0.02 kg day−1, respectively (P = 0.17). In the SGS, all heifers were treated with ivermectin on day 431 due to clinical signs of respiratory disease. The ADG for control and TST heifers from turnout on day 321 to day 431 was 0.90 ± 0.04 and 0.80 ± 0.04 kg day−1, respectively (P = 0.03). Conclusions Spring-born FGS suckler beef calves require minimal anthelmintic treatment to maintain performance. In contrast, clinical parasitic disease may develop in the SGS unless appropriate anthelmintic treatment is provided.