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Epidemiology of Gastrointestinal Nematodes in a Naturally Infected Ontario Cow-Calf Herd: Efficacy of Fenbendazole and Ivermecin

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Title: Epidemiology of Gastrointestinal Nematodes in a Naturally Infected Ontario Cow-Calf Herd: Efficacy of Fenbendazole and Ivermecin
Author: Mackie, Kaley
Department: Department of Population Medicine
Program: Population Medicine
Advisor: Gordon, JessicaMenzies, Paula
Abstract: This thesis investigates the epidemiology of gastrointestinal nematodes in a naturally infected pastured, spring-calving cow-calf herd in southern Ontario. In addition, it examines the efficacy of two anthelmintics on fecal egg counts (FEC) and animal performance. In each of 2014 and 2015, 64 cow-calf pairs were randomly assigned to one of three treatment groups: oral fenbendazole, topical ivermectin, or negative control. Treatment groups were randomly subdivided into field groups and assigned to a rotationally grazed field at the Elora Beef Research Centre. Weights, body condition scores (cows), and fecal samples were collected from every animal before treatment, on day-14 (in 2015) and then at 28 d intervals. Animals were placed on pasture immediately after treatment. In control calves, FEC were zero at treatment and peaked after 55 to 72 d on pasture at 24 epg (95% CI 15.82, 37.2). In control cows, FEC were initially higher 3 epg (95% CI 1.75, 4.39), declined after placement on pasture and rose again to peak at 4 epg (95% CI 2.57, 6.32), the same time as calves. Negative control cows had 1.35 (95% CI 0.92, 1.99; P = 0.11) and 2.14 (95% CI 1.46, 3.14; P = 0.0009) times more eggs per gram then the fenbendazole and ivermectin treatment groups respectively. Treatment did not have a significant effect on calf FEC or weaning weight or cow pregnancy rates. Four different fecal egg count reduction tests (FECRT) were compared in 2015. They all suggested some level of anthelmintic resistance (AR) to both fenbendazole and ivermectin (percent FEC reduction ranging from 64.8 to 96.9% with lower 95% CI ranging from 26.4 to 67.2%), despite the fact that this herd had very little history of anthelmintic use. This thesis shows the importance of continued work on anthelmintic treatment and efficacy in cattle.
URI: http://hdl.handle.net/10214/9678
Date: 2016-05


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