Mitigating the effects of gastrointestinal nematode infection in organic lambs through the use of hospital paddocks

Abstract

This thesis investigated the use of a hospital paddock treatment comprised of chicory (Cichorium intybus), plantain (Plantago lanceolata) and red clover (Trifolium pratense) in place of anthelmintic treatment to provide a curative effect for gastrointestinal nematode infections in organic lamb production systems. Furthermore, in order to improve the agronomical restrictions caused by having large areas of farmland planted in these bioactive forages, a targeted selective treatment (TST) regime was used to identify only those individuals that were suffering from parasitism and thus expected to obtain a benefit at any point in time. The study was conducted at the Biological Husbandry Unit in Lincoln University, from December 2012 to April 2013 using sixty four, three month old Suffolk crossed lambs; thirty-two lambs each were allocated to graze one of two organic perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) paddocks infected either with Teladorsagia circumcinta (TCIRC) or Trichostrongylus colubriformis (TCOL). Within each parasite treatment, eight lambs were allocated to a drench control treatment to provide an estimate of the potential performance that could be achieved (TCIRC-D and TCOL-D), while the remaining twenty four lambs were subjected to a TST regime (TCIRC-TST and TCOL-TST). Individual live weight (LW) and faecal samples were monitored every two weeks. A pre-set LW gain of each lamb was calculated using the Happy factor system and at each decision time, TST individuals that did not achieve their target LW were removed from pasture and allowed to graze on the hospital paddocks for four weeks before being returned to pasture. Overall, cumulative LW of TST individuals was lower than their drenched counterparts; being statistically similar on Day 0 – 51, with significant differences evident from Day 79 for the TCIRC-TST and from Day 65 for the TCOL-TST animals relative to their drenched controls. Consequently, an overall 32% and 39% reduction in growth; viz., 13.47 ± 1.06 cf. 19.97 ± 1.63 kg and 13.32 ± 0.65 cf. 21.96 ± 1.27 kg for the TCIRC-TST and TCOL-TST group, respectively was observed, which was generally associated with temporal variations in size of larval challenge and herbage mass, and the interaction of these two factors with individual lambs. Performance of the TST lambs challenged with both parasite species improved to similar levels with those of the drench control after four weeks of hospitalisation. This was believed to be related to the quality of the bioactive forages as there was no evidence of a direct anthelmintic effect of the bioactive forages. Despite high FEC, mean LW from Day 79 was 39.1 kg and 36.2 kg for the TCIRC-TST and TCOL-TST lambs, respectively, suggesting that this approach was able to allow 80% and 58% of lambs to reach the required market weight of 38 kg without the use of anthelmintic. The overall observation supports the hypothesis that hospital paddock treatment using bioactive forages was able to partly mitigate the effects of infection and maintain reasonable lamb performance in an organic context. The benefit of the use of such approach appeared to be greater in abomasal than intestinal infections.