Knowing Your Enemy: Canadian Researchers Help Organic Sheep Producers Understand Parasites

Organic Agriculture Centre of Canada

Sheep happily grazing a pasture – an idyllic pastoral scene that brings to mind the interconnectedness of agro-ecosystems.  As the sheep graze, they fulfill their nutritional requirements, while weeding and fertilizing the pasture.  It represents a synergistic system, the goal of organic producers.  Yet on closer examination, the system is not so perfect. 

The Canadian Organic Standard mandates that organically raised livestock cannot be treated with products such as antibiotics and anthelmintics, except when the health of the animal is imminently threatened.  The treated animal must then be handled separately.  Additionally, the standard stipulates that ruminant livestock must have access to pasture when weather conditions permit, and at least 60% of the ruminant diet is to be composed of forages.  However, ruminants are susceptible to infection with gastro-intestinal nematodes (GINs) when grazing pasture.  These parasites adversely affect animal welfare, reduce weight gains and occasionally cause severe illness and death.  Sheep are particularly at risk of GIN infection, as they tend to graze plant tissue to a low level, close to the soil surface where these parasites commonly reside. 

Facing these challenges, what strategies should organic producers follow to reduce losses from GIN infection?  These strategies are also of value to conventional producers, not just to limit the risk of anthelmintic resistance but also to reduce drug and labour costs associated with chemical treatments.

Researchers in Canada saw the need to better understand the GIN parasites that are prevalent in Canada in order to develop management systems and tools that can help producers raise healthy animals in the absence of synthetic drugs and pesticides.  The resultant findings have been recently published in a paper in Veterinary Parasitology, entitled “Prevalence and distribution of gastrointestinal nematodes on 32 organic and conventional sheep farms in Ontario and Quebec, Canada (2006-2008)”.  It had been three decades since a Canadian study had thoroughly examined the dynamics of GINs in this country.  Lead author America Mederos explains “There is not a simple solution to effectively control GINs regardless of the type of production system; therefore, epidemiological studies are crucial when studying or implementing some of the proposed alternative control measures.”  In other words, in order to effectively implement alternative management strategies, such as grazing management, rotational grazing, selective breeding and improved feed quality, a thorough understanding of GINs is needed.  

The study  included operations that were certified organic, followed organic practices and principles but were not certified, or used conventional management practices but with minimal use of anthelmintics.  Monthly sampling during the grazing season allowed researchers to track the body condition of the subject animals (both ewes and lambs), as well as parasite levels on pastures and in fecal samples.   Necropsies were also performed in lambs from a subset of farms to further evaluate the infecting nematodes.  From these data, researchers aimed to identify the peak periods of infection and the most prevalent infective nematode species. 

Ewes were found to have the highest levels of parasites in the spring months (April – June), while lambs had the highest infestations in the summer months (July – September) and pasture forage levels peaked in late summer and fall.  The authors suggest that the peak infestation in ewes is a result of lowered immunity during pregnancy and lambing, while the later peak in GIN infection in lambs is driven by contamination of the pasture that occurs when the infected ewes graze in the spring.  Interestingly, climatic differences between the two provinces studied resulted in slight differences in infection patterns.   Yet, the study revealed that the patterns of infection on conventional and organic farms did not differ. 

Mederos explains that “The main species of GIN which parasitize sheep worldwide were found in the study.”  The most prevalent species were Teladorsagia sp and Trichostrongylus spp, both believed to be important species in temperate regions.   The warm climate species Haemonchus contortus (also known as the “Barber pole worm”) was also discovered on the Canadian farms in the summer.   Knowledge gathered in other areas can therefore potentially help Canadian farmers manage these species, now that farmers know exactly what parasite species are involved. 

While this study is a strong starting point for research that can help guide organic producers in the management of their sheep and pasture, Mederos stresses that “the communication and collaborative work between researchers, farmers and practitioners is very important and should continue”.

This article was written by Joanna MacKenzie on behalf of the OACC with funding provided by Canada’s Organic Science Cluster (a part of the Canadian Agri-Science Clusters Initiative of Agriculture and Agri-Food Canada's Growing Forward Policy Framework).  The Organic Science Cluster is a collaborative effort led jointly by the OACC, the Organic Federation of Canada and industry partners
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Posted December 2010