Strategic control of gastrointestinal nematodes in grazing sheep with a long-acting moxidectin formulation

Abstract

A field study was undertaken on three Swiss sheep farms (A, B, C) to evaluate the efficacy of a long-acting moxidectin formulation (Cydectin® 2% LA) against gastrointestinal nematodes (GIN). Naturally infected ewes (all three farms) and their winter-borne lambs (farms A and B) were allocated to two groups (MOX, CON). At day 0 ewes of the MOX-groups were treated with 1mg moxidectin s.c. CON-and MOX-groups were grazed on separate pastures and were sampled for faeces and blood at 28-day intervals. Based on larval cultures Haemonchus contortus was the dominant GIN-species in ewes throughout the season. Over the entire observation period faecal egg count (FEC) of the MOX-ewes in farms A, B, C was 56, 84 and 87% less than the CON-ewes (p<0.05). FEC of lambs grazing with MOXewes was reduced in farms A and B by 56% and 61%, respectively (p<0.05), compared with the respective CON-groups. None of these lambs received anthelmintic treatment during the experiment. Therefore, the differences were due to an indirect effect mediated by the lower pasture contamination with GIN-larvae. These were reduced by 73, 81 and 74% in farms A-C respectively compared to the CON-groups (p<0.05). In farm B, where lambs remained with their mothers during the entire grazing season, these differences were also reflected by a higher daily weight gain (p<0.05) and reduced pepsinogen levels in lambs of treated ewes. This strategy offers an interesting potential for expanding refugia by propagation of GIN in untreated lambs. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Page 1 of 33A c c e p t e d M a n u s c r i p t 1 Highlights 1 A long-acting moxidectin formulation (Cydectin® 2% LA, Zoetis) administered to ewes in three farms 2 reduced the excretion of gastrointestinal nematode (GIN) eggs by 56, 84 and 87% resp. compared 3 with untreated controls (p<0.05) in an Haemonchus contortus dominated environment. 4 GIN egg shedding of untreated lambs grazing with moxidectin-treated ewes was reduced by 56% and 5 61%, resp. (p<0.05) mediated by the lower pasture contamination with GIN-larvae. 6Untreated lambs grazing with moxidectin-treated ewes exhibited a higher daily weight gain 7 compared with lambs from untreated ewes (p<0.05). Abstract 20A field study was undertaken on three Swiss sheep farms (A, B, C) to evaluate the efficacy of a long-21 acting moxidectin formulation (Cydectin® 2% LA) against gastrointestinal nematodes (GIN). Naturally 22 infected ewes (all three farms) and their winter-borne lambs (farms A and B) were allocated to two 23 groups (MOX, CON). At day 0 ewes of the MOX-groups were treated with 1mg moxidectin s.c....

Short communication: A practical farm-based trial to compare ewe nematode control strategies in peri-parturient ewes

“…The lower ewe FECs in the LA group had a consequent impact on lamb FECs; those lambs born to ewes receiving long-acting wormer had the lowest FECs (Fig 2). The results of this study are in keeping with the findings of [18] who found lambs grazing with dams treated with long-acting moxidectin to have reduced FECs of 56% and 61% on two farms studied as compared to those whose dams were untreated [16] also found reduced FECs of lambs whose dams had been treated with long-acting moxidectin as opposed to a short-acting oral moxidectin. Reductions in lamb FECs could result in fewer or no anthelmintic treatments of the lambs, positively impacting on selection for anthelmintic resistance in the helminth population on a given farm, as well as reducing economic costs and labour time.…”

“…Lambs in the study by [ 18 ] were also found to have statistically significant higher DLWGs on one farm if their mothers had received a long-acting moxidectin treatment. In the present study, although the lambs whose mothers received long-acting moxidectin did have the highest DLWG of all the groups from shearing of the ewes to weaning it was not found to be statistically significant.…”

“…This is disputed by some who suggest that helminths are exposed to lethal drug concentrations for longer periods when a long-acting moxidectin is used, therefore resistance is only selected for in the latter weeks of cover when the concentration within the animal dips beneath the lethal concentration, similar to short-acting wormers [16]. Research has shown that the terminal slope of serum concentrations is close to parallel for both the dose rate of short-acting and long-acting moxidectin, indicating that parasites would not be exposed to sub-lethal doses for any longer when the long-acting anthelmintic is administered [18].…”

Effectiveness of the new Iverlong prolonged-release drug for gastrointestinal nematodoses in sheep

“…A number of authors note from macro cyclic lactones the high efficacy of the Moxidectin drug, it is a highly lipophilic macro cyclic lactone endoctocide. It is many times more effective than Ivermectin against gastrointestinal nematodes, being effective against Ivermectin-resistant strains, such as Haemonchus contortus and Trichostrongylus colubriformis, and also has a long therapeutic effect [2][3][4].…”