Characterization of the population dynamics and impact of gastrointestinal nematodes in organic sheep farms in Ontario & Quebec

BOND, ERIN; SUDEMAN, ROBYN; FERNÁNDEZ, ALICIA SILVINA; MENZIES, PAULA; PEREGRINE, ANDREW

Jornada; OVC Summer Leadership Program Poster Presentations; 2006

Ontario Veterinary College

Investigations have shown that nematode parasites are the greatest economic constraint to grazing livestock production in both developed and developing countries. Associated deleterious effects of intestinal nematodes are reduced feed intake, reduced weight gain, weight losses, lower milk production, reduced carcass quality, poor wool production and death. Traditional methods of gastrointestinal parasite control utilize the periodic use of anthelmintics. However, over the last two decades there has been a substantial increase in the incidence of anthelmintic resistance. Furthermore, organic farming precludes the use of anthelmintic drugs. Unfortunately, little is known about the epidemiology of gastrointestinal nematodes in sheep in Canada and therefore how they can best be controlled. Such information is particularly important for organic farmers. A three year observational study was initiated in May 2006 in which 30 organic and conventional farms were visited monthly. In May 2006, 10 ewes and 10 lambs were randomly selected per farm. Fecal samples were collected every 4 weeks during the pasture season and analyzed to obtain the number of gastrointestinal nematode eggs per gram of feces (epg) using a modified McMaster technique. Samples were also examined using a Baermann technique for the presence of lungworm larvae. Blood samples were collected from study animals at the onset of the pasture season and processed to obtain total protein and hematocrit levels. The Dag score, body condition score, and fecal consistency score of all research animals were recorded and evaluated at each visit. Grass samples were collected from the pasture(s) where animals were grazed each month. Pasture samples were processed using an agar technique to obtain L3 larvae, which were analyzed to quantify and differentiate types of infective larvae present. Questionnaires were administered on each farm to collect information on the animals’ breed, age, number of seasons on pasture, farm climate data, stocking density, length of grazing season, anthelmintic use, etc. Results: There was a general trend for the ewes’ epg values to decline from the May/June visit to the June/July visit. The initial increased level is most likely to be attributed to periparturient relaxation of immunity. There was a general trend for the lambs’ epg values to increase from the May/June visit to the June/July visit. The increasing levels of lamb gastrointestinal nematode epgs may be attributed to being turned out on pastures infected at the beginning of the grazing season. Hematocrit and total protein levels obtained from all animals on all farms for the initial blood sampling, during the May/June visit, were found to be within normal parameters. The pasture L3 larvae burdens at the beginning of the 2006 grazing season (i.e. May/June) are given in Figure 3 - large variability was observed between farms. There was also evidence on some farms that gastrointestinal parasites over wintered on pasture. This variability is most likely attributed to different management practices on each farm. Further investigations are required to determine the exact levels of over wintering on each farm. In addition, work is required to identify management practices associated with low parasite burdens in sheep; the large variation in parasite data observed on the described farms indicates that it should be possible to identify these management practices with a long-term prospective study.