Gastrointestinal nematodes on organic sheep farms and sustainable parasite control measures

A. Mederos^1,2, A. Peregrine³, S. Fernández^1,3, P. Menzies², J. VanLeeuwen⁴, D. Kelton³ and R. C. Martin^a

Abstract
When sheep are raised on pasture they typically become infected with gastro-intestinal nematodes (GIN). Internationally, the sheep industry faces an increasingly severe production-limiting problem with resistance of the major species of GIN to all classes of dewormers. Because of this, sheep production has almost ceased in some regions. Thus, producers on conventional farms must adopt alternative control methods if sheep production is to remain sustainable.

Similarly, since the sheep industry has embraced organic production, alternative methods must be adopted in order to prevent severe disease problems due to gastrointestinal parasitism.

In order to provide sound advice on alternative control methods, a thorough understanding of the epidemiology of GIN in Canada is required - unfortunately, no work has been carried out in this area in Canada for over 40 years. To address this issue a 3-year study was conducted using 32 sheep farms (23 in Ontario, 9 in Quebec) that used no dewormers or had minimal use of dewormers.

Over the course of 3 grazing seasons (2006-2008), work was carried out with 10 adult ewes and 10 ewe lambs on each farm; feces and pasture samples were collected monthly from each animal; blood samples were collected twice a year.

The following clinical parameters were also monitored: body condition score, dag score (soiling of wool from diarrhea), anemia and fecal consistency. In order to obtain definitive information on the parasite species infecting sheep, necropsies were carried out on lambs from 7 farms. Information on management practices that influence GIN numbers was also collected.

The most significant findings from the study were as follows:

GIN were detected on all sheep farms throughout the study. However, among the farms there was large variation in the parasite burdens in sheep and on pasture. In general, the time of the year when fecal egg counts were at their highest differed between ewes and lambs: ewe counts peaked in spring (April-May), while lamb counts peaked during the summer (July-August). This indicated that ewes play a significant role in contaminating pasture at the beginning of the grazing season. As a result, ewes that lamb in the spring should receive preventive deworming at lambing; and lambs on such farms should be dewormed at 4 to 8 weeks of age. The results also indicate that annual monitoring of parasite egg output in sheep feces should be carried out in May for ewes and in July for lambs.
The most common GIN species diagnosed by examination of fecal and pasture samples were Trichostrongylus, Teladorsagia and Haemonchus species. Thus, information on parasite control in sheep from parts of the world where Haemonchus predominates (e.g. southern USA) is not necessarily applicable to Ontario and Quebec sheep producers.
Manure application on pasture during the previous year was shown to increase the risk of parasitism in sheep - Data from this study was used to generate a picture of the farm management practices, then modeled with computer software developed in the United Kingdom to determine the predicted level of parasitism in lambs over a season.
The results of comparing model predictions to actual data showed that on most Ontario farms the values were generally very similar, and that the model was able to predict fecal egg counts reasonably well for the grazing seasons in 2006 and 2007. Where the model did not make accurate predictions, it was determined that abnormalities in weather and extreme differences in farm practices were the primary cause(s). Further work with this model should result in the development of a parasite management tool for producers and their veterinarians.

The benefit to society from this work will be reduced costs associated with sheep production from savings both on drugs and labor, improved productivity because of lower disease rates, a reduced risk of development of anthelmintic resistance, improved welfare for sheep by disease avoidance, and application of sound science to sustainable production of organic sheep.

Source
Final project summary report to Natural Sciences and Engineering Research Council (NSERC), July 2009

Author Locations and Affiliations
(1) Organic Agriculture Centre of Canada, Nova Scotia Agricultural College, Truro, NS;
(2) Dept. of Population Medicine, Ontario Veterinary College, University of Guelph, Guelph, ON;
(3) Dept.of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON;
(4) Dept. of Health Management, Atlantic Veterinary College, Charlottetown, PEI

en français

Posted July 2009


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Research Extension Courses Consumers -------------------------- Virtual Tours Student & Job Opportunities News Articles Standards -------------------------- Market Information Events Issues Animal Welfare Strategic Plans -------------------------- Links Award-winners Site Map	Gastrointestinal nematodes on organic sheep farms and sustainable parasite control measures A. Mederos^1,2, A. Peregrine³, S. Fernández^1,3, P. Menzies², J. VanLeeuwen⁴, D. Kelton³ and R. C. Martin^a Abstract When sheep are raised on pasture they typically become infected with gastro-intestinal nematodes (GIN). Internationally, the sheep industry faces an increasingly severe production-limiting problem with resistance of the major species of GIN to all classes of dewormers. Because of this, sheep production has almost ceased in some regions. Thus, producers on conventional farms must adopt alternative control methods if sheep production is to remain sustainable. Similarly, since the sheep industry has embraced organic production, alternative methods must be adopted in order to prevent severe disease problems due to gastrointestinal parasitism. In order to provide sound advice on alternative control methods, a thorough understanding of the epidemiology of GIN in Canada is required - unfortunately, no work has been carried out in this area in Canada for over 40 years. To address this issue a 3-year study was conducted using 32 sheep farms (23 in Ontario, 9 in Quebec) that used no dewormers or had minimal use of dewormers. Over the course of 3 grazing seasons (2006-2008), work was carried out with 10 adult ewes and 10 ewe lambs on each farm; feces and pasture samples were collected monthly from each animal; blood samples were collected twice a year. The following clinical parameters were also monitored: body condition score, dag score (soiling of wool from diarrhea), anemia and fecal consistency. In order to obtain definitive information on the parasite species infecting sheep, necropsies were carried out on lambs from 7 farms. Information on management practices that influence GIN numbers was also collected. The most significant findings from the study were as follows: GIN were detected on all sheep farms throughout the study. However, among the farms there was large variation in the parasite burdens in sheep and on pasture. In general, the time of the year when fecal egg counts were at their highest differed between ewes and lambs: ewe counts peaked in spring (April-May), while lamb counts peaked during the summer (July-August). This indicated that ewes play a significant role in contaminating pasture at the beginning of the grazing season. As a result, ewes that lamb in the spring should receive preventive deworming at lambing; and lambs on such farms should be dewormed at 4 to 8 weeks of age. The results also indicate that annual monitoring of parasite egg output in sheep feces should be carried out in May for ewes and in July for lambs. The most common GIN species diagnosed by examination of fecal and pasture samples were Trichostrongylus, Teladorsagia and Haemonchus species. Thus, information on parasite control in sheep from parts of the world where Haemonchus predominates (e.g. southern USA) is not necessarily applicable to Ontario and Quebec sheep producers. Manure application on pasture during the previous year was shown to increase the risk of parasitism in sheep - Data from this study was used to generate a picture of the farm management practices, then modeled with computer software developed in the United Kingdom to determine the predicted level of parasitism in lambs over a season. The results of comparing model predictions to actual data showed that on most Ontario farms the values were generally very similar, and that the model was able to predict fecal egg counts reasonably well for the grazing seasons in 2006 and 2007. Where the model did not make accurate predictions, it was determined that abnormalities in weather and extreme differences in farm practices were the primary cause(s). Further work with this model should result in the development of a parasite management tool for producers and their veterinarians. The benefit to society from this work will be reduced costs associated with sheep production from savings both on drugs and labor, improved productivity because of lower disease rates, a reduced risk of development of anthelmintic resistance, improved welfare for sheep by disease avoidance, and application of sound science to sustainable production of organic sheep. *Source* Final project summary report to Natural Sciences and Engineering Research Council (NSERC), July 2009 *Author Locations and Affiliations* (1) Organic Agriculture Centre of Canada, Nova Scotia Agricultural College, Truro, NS; (2) Dept. of Population Medicine, Ontario Veterinary College, University of Guelph, Guelph, ON; (3) Dept.of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON; (4) Dept. of Health Management, Atlantic Veterinary College, Charlottetown, PEI en français Posted July 2009
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Gastrointestinal nematodes on organic sheep farms and sustainable parasite control measures

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