Managing Internal Parasites in Organic Livestock

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Av Singh, Ph.D.

Internal parasitism is considered to be one of the most prominent livestock diseases in Canada causing economic and production losses to many ruminant livestock producers. For organic producers recourse to synthetic dewormers (i.e., anthelmintics or parasiticides) is severely restricted and in some cases prohibited. Furthermore, increased resistance to dewormers, harm to non-target species (e.g., species that help decompose manure), and growing concerns regarding parasiticide residues in meat has some producers searching for viable alternatives. This article will highlight the many innovative practices used by livestock producers to limit parasite infestation and will describe some alternative parasiticides to conventional dewormers.

Animals that graze are often being exposed to parasites and the likelihood of being reinfected is greater than those animals kept in confinement. Therefore, internal parasites may pose a greater challenge for organic livestock producers because of their tendency to be more reliant on pastures. For most organic producers a "zero tolerance" policy for internal parasites is not a desirable goal. First, the implementation of several preventative practices may not be economically feasible; and secondly many producers want their animals to have controlled exposure to parasites to help build immunity. So, ideally the ultimate objective is to develop an animal production system in which parasites may be present in small numbers but do not affect the health or performance of the animal.

Herd Management:

An animal is better able to resist or tolerate internal parasites when its living conditions are good. In barns, animals should be fed using feeders rather than directly from the ground thereby avoiding contamination as a result of their mouths coming in contact to bedding or manure. With respect to nutrition, vitamins and minerals can play a key role in affecting ruminant susceptibility. Vitamins A, D, and B complex are integral in developing immunity to parasites, while cobalt (used to synthesize vitamin B12) and iron are essential minerals.

Pasture Management:

Increased stocking rates have a direct correlation with increased parasite load and therefore if parasite infestation is a problem then lower stocking densities are recommended. Lowering the animal density serves two purposes; first it reduces the amount of manure in a given area, and secondly the residual grazing height is often much higher. Leaving a residue greater than 10cm will lower the probability of parasite infection significantly considering 80% of parasites live in the first 5cm aboveground. The risk of infection is also lowered by waiting to put animals out to pasture after the dew has lifted or until the grass has dried after the rain. Drier conditions force parasites to stay at the base of plants and therefore less likely to be harvested by grazing.

A very useful concept in parasite control involves the use of safe or clean pastures. Pastures that have been harvested for hay, silage, or small grain crops can generally be considered safe. Pastures that have been grazed by other species for a grazing season or longer are considered safe because only a small amount of cross infection between species occurs.

Sheep relative to cattle tend to be more susceptible to internal parasitism because of their ability to graze close to the ground. Moreover, sheep manure is excreted in pelleted-form
Permitting sheep to graze directly over their manure, in contrast to cattle that will avoid grazing near dung pats. As such, integrating animals with differing susceptibilities to parasites, such as cattle and sheep grazing together or grazing following each other has been shown to reduce parasite load in pastures. Similar to multispecies grazing, livestock producers will often mix different classes of animals to reduce parasite infection. Lambs and calves will often have access to pastures prior to ewes and cows, respectively. Some organic producers will attempt to build immunity in young calves by placing them with dry cows that serve as a controlled source of infection.

Different forage species may also have a role in determining the parasite load within a pasture. Generally, grass-dominant pastures contain more parasite larvae than pastures containing legumes such as alfalfa and birdsfoot trefoil (owing primarily to increased levels of condensed tannins) or forbs like chicory.

The common practice of harrowing pastures to break up dung pats is generally not recommended. Dragging manure pats across pastures may scatter parasite eggs and larvae, making it difficult for animals to selectively graze away from infected areas. Harrowing pastures may prove beneficial just prior to a dry period in which the pasture would be rested for a long period. Alternatively, dung-burying beetles and free-ranging chickens help breakdown dung pats, reducing the environment for parasite infestation.

Alternative Dewormers:

As a last resort, livestock producers can carry out deworming treatments as a means of parasite control. All deworming treatments involving natural products should ideally be preceded by a fasting period and followed by a laxative period. Many of these natural dewormers can be considered poisons and it is therefore essential to follow indicated dosages. Alternatively, most botanical dewormers can also be found as homeopathic preparations, which when administered are free of side effects and do not require a fasting or laxative period.

Some common botanical dewormers include; garlic (pills, powders, fresh, tinctures); wormwood (Artemisia spp.); wild ginger or snakeroot; goosefoot; conifers (pine, spruce, or fir); mustard; squash or pumpkin seeds; carrot and fennel seeds; pyrethrum (plant extract from Chrysanthemum); and several others. Other products used as dewormers include; diatomaceous earth and charcoal which are often added to the ration; peroxide, copper sulphate, and Shakelee's Basic H surfactant (Joel Salatin swears by it, but it may not be accepted by certain organic certifying bodies) are administered as solutions with water.

Despite having use of alternatives to synthetic parasiticides, organic farmers are relying on fine-tuning their nutrition regimes, herd and pasture management, as well as field and soil practices so they can learn to coexist with parasites. The OACC, in collaboration with the New Brunswick Department of Agriculture and Fisheries, and the Atlantic Veterinary College at the University of Prince Edward Island have initiated an assessment of parasite load in organic and transitional beef herds. The trial will also survey farmer-cooperators to determine what farming practices may contribute to the level of parasitism observed on the farm.

For more information please call the Organic Agriculture Centre of Canada at 902-893-7256 or email oacc@nsac.ca