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Internal Parasites and Ruminants: Organic Answers
This article was first printed in the November - December 2005 issue of the Organic Broadcaster, published by the Midwest Organic and Sustainable Education Service.
At Jump River Sheperd's Dairy, Rich Toebe and Kim Cassano have managed a sheep dairy flock for about six years. Located in north central Wisconsin, they rotationally graze their flock of around 200 animals through flat permanent paddocks of nicely diverse grasses and forbs.
On a recent visit in the early fall, I was impressed by the health and vigor of the flock and asked about Rich's plan for parasite control. Using organic management practices for the past 3 years, Rich responded to my question in this way: "We basically do little to specifically manage for parasites anymore. We've been working on fine tuning nutrition, pasture management, culling for heartiness and parasite resistance, combined with the limited use of some herbal wormers. I believe that the sheep are so healthy that parasites, when present, seem to have minimal affect on the animal's health."
Anyone who has toyed with small ruminant management may be as surprised as I was, as a newer sheep producer, to hear Rich's answer. When one reads any conventional literature on sheep or goat production, the challenge of parasite load quickly rises to the top as a primary health management concern. Those with cow dairy herds or horses have also been led to believe that regular worming is critical to their animal's, ( and more particularly youngstock's), health. An ATTRA publication, "Integrated Parasite Management for Livestock" states that "Internal parasites are considered by some to be one of the most economically important constraints in raising livestock."
Conventional animal managers are finding themselves up against a huge challenge in parasite control- in the past several years most of the chemical wormers (anthelmintics such as Ivermectin) on the market have become ineffective. Parasite resistance has built up to such a degree to all but a very few wormers that even conventional farms, generally quick to turn to their drug cabinet, are being told to restrict chemical wormer use and instead explore alternative management and controls.
As Rich points out, there are several keys to maintaining control over ruminant parasites. They include: understanding parasite life cycles, pasture management, proper animal nutrition, breeding for parasite resistance and the use of natural parasite controls. The same basic principles hold true whether you hear mooing, baaing or bleating in the morning as you go out to do chores.
Symptoms of infection vary with the type of parasite involved, but generally a severely infected animal will have their head down and ears drooped. Body condition will deteriorate, the coat will get rough in cows and goats. Diarrhea may or may not be involved. An infected animal may show weight loss, but be careful that it could also be sign of other diseases (Scrapie, Johnes). Blood sucking worms can cause anemia in the host animal.
The majority of the life cycle of any parasite will occur outside the animal. Understanding the timing and ideal conditions of these periods is key to succeeding at parasite management. The way you manage your soil, manure, feedstuffs and pasture will dictate the load of parasites your animals will have to deal with.
Parasite egg survival is very weather dependent. Eggs thrive in warm, moist conditions. In normal climatic years worm larvae numbers on pastures peak in July and August. This peak moves back in the fall if the summer is dry and followed by a wet fall. Parasites will die in hot and dry, or very cold conditions. When it is warm, parasite numbers will grow quickly on the pasture. When it is cool, eggs will even survive longer. Some parasite eggs will survive the winter in the north, some will survive longer than a year in their dormant stage. Snow cover will insulate the larvae and allow them to survive.
Most internal parasites rely on the fecal-oral route for transmission, and so cleanliness and manure management are extremely important in control of exposure. Concentration of animals will cause concentration of parasites. A dry manure pack tends to discourage parasite development. Proper manure composting will kill parasite eggs and larvae. Barn lime in stalls and pens acts as a drying agent and will kill worms and larvae.
Parasite levels can test high in very young animals- even at 1 month of age cow research shows. Once a cow gets to be 2 years of age, resistance has built up and an immune system response has set in, so generally you see less effect of parasites. Youngstock that is born later in the year tends to be more susceptible to parasites, as they have not yet built up an immunity when the parasite load on the pasture is heavy. Loads will be heavier in animals recently post partum, as their immmune function decreases immediately following birth.
Because sheep graze close to the ground they tend to be more susceptible to internal parasites than other animals. Most parasite larvae don't climb higher than 5 inches from the ground. An animal that grazes higher will be less likely to ingest them.
Parasites common in ruminants
Ostertagia Circumcinta, the small brown stomach worm, (roundworm) is the second most common parasite in sheep and goats, and the most economically significant in cattle. They are ingested through grazing and hook themselves to the mucus membranes of the small intestine where they mature. Once there it causes digestive disturbances, diarrhea and weight loss.
Tape worms (Taenia species) require pasture mites (or fleas for dogs and cats) to complete their life cycle, and generally won't cause significant symptoms in the host animal. In extreme cases tapeworm infestations can cause diarrhea, weight loss and possibly death.
Goats and sheep pick up lungworms (Dictyocaulus species) when they consume larvae in feces. The larvae pass into the small intestine, penetrate the intestine wall and then travel through the blood to the lungs where they can cause respiratory problems in severe cases. Normally there aren't any obvious clinical signs associated with lungworms. Programs of control for stomach worms generally also control lungworms.
Liver flukes Fasciola hepatica require an alternate host (snails) and require open water to complete their life cycle. They can be controlled by limiting access to standing water or working to eliminate snails. Whenever conditions are appropriate to support snails, liver flukes may be present. Only a few liver flukes can have an economic impact on your herd or flock. Liver flukes will be killed by 30 or more days below freezing, and so infections in our northern climate will occur from eggs deposited in the spring, leading to infections in August or September and no eggs in fecal counts until December or January.
Coccidia are one celled parasites that kill cells lining the intestine. They are picked up from feeding areas, where manure makes it onto feed, and also dirty water. Coccidia are generally not a problem on pasture. Each species has its own unique coccidian species, and young lambs and goats are especially susceptible to infection. Coccidia has a 28 day life cycle, and they reproduce in the animal's small intestine. Symptoms include blood in manure, which indicates intestinal damage. Common in poultry. Coccidia is hard to determine from fecal samples, as eggs are not shed evenly.
To get a sense of the life of a parasite, we will give you the full detail of H. contortus life cycle: Eggs are shed in the host animal's feces by parasites that are in their adult (fifth) stage of development, while the parasites are attached to the animal's abomasum. First stage larvae develop from eggs and hatch in a day or two, ready to feed on microorganisms found in manure. After a molt, the second stage larvae also feed on microorganisms, but they must have contact with soil and warm, wet conditions. This stage averages about 18-20 days. The second stage molt is started but not completed in the external environment. The infective third stage larvae remain encased in the cuticle of the second stage until it is ingested by an animal. At this stage the larvae are most vulnerable to environmental extremes and most dangerous to grazing youngstock. The larvae climb on grasses in warm, wet conditions. They will die from exposure in dry and hot or cold conditions. Once ingested the sheath is cast off in the abomasums of the animal, and the now parasitic third stage larvae attach to the animals abomasum and suck blood. The fourth stage soon molts into the fifth (adult) reproductive stage. Animals may carry the fourth stage parasites in their abomasums in a hypobiosis (arrested development) stage through the winter, They will then shed eggs in the spring while on pasture. If this happens the adult animals will be infected but the parasites are inactive and not reproducing. The cause or duration of hypobiosis is unknown. One H. Contortus female may pass on as many as 10,000 eggs per day (under favorable conditions).
The temptation with the spring flush of pasture growth is to move animals through paddocks quickly, 10-20 days growth, to keep up with fast forage growth. Unfortunately, this will only optimize conditions for parasite contamination, and thus magnify problems throughout the remainder of the year. Most of the parasites that are at issue for ruminants in the north will have a re-infection rate of between 20 and 30 days. Grazing management should be designed so that paddocks are not re-opened to the same or similar species within less than 30 days.
As much as possible clean pasture should be used. For this purpose, clean pasture can be defined as: not grazed for 12 months, used previously for hay, or grazed by species in another group. Sheep and goats host the same parasite species. Cows are somewhat different, horses and hogs will carry different parasitic species. Poultry will carry yet different parasites. Because parasites only crawl a limited height on grass swards, it is important to not graze pasture below 2". If managing the rotation is a challenge, consider running cows between sheep rotations if pasture grows too fast. Run cows first to get the grass short enough for the height sheep prefer.
Soil organisms, such as earthworms, dung beetles and fungi will destroy many parasite eggs. The longer they are left to their work, the cleaner your pasture will be. Managing pastures to favor soil microorganisms will reduce parasite levels.
The longer manure stays intact on pastures the longer parasites will survive there. Factors that reduce manure integrity, such as scratching by chickens of breakdown by insects will reduce parasite larvae survival. Don't force grazing close to manure. Parasitic larvae generally will migrate no more than 12 inches from a manure pile.
Use a leader/ follower system if possible, with older, more resistant animals grazing first, then followed by youngstock. Consider splitting your farm into two, grazing sheep on one half and cows or horses in the other half in year one, then flipping sections for year two- thus giving the equivalent of 12 months break between parasite loads for each species.
Plants with high tannins have been proven to be effective in parasite management: birdsfoot trefoil, chickory, dock, young plantain, echinacea, raspberry canes and roots. Research has shown that intake of high-tannin forage can reduce parasite load by 50%. It is ideal to set aside an "herbal pasture" which contains a diversity of plants with high tannin content. Animals can be turned into this pasture at special times when you want them to get a heavy does of beneficial weeds. They can self-select the weeds that will do them the most good. Although pasture diversification in itself is a good idea, animals will choose weeds first, so will put too much pressure on beneficials if they have regular exposure.
Good nutrition in early pregnancy increases fat stores and has been shown to increase the immune response to parasites. Increased protein levels during late gestation will produce an increased ability to fight parasites.
Research has shown that approximately 80% of worm problems will come from 20% of your animals. Research done by Crystal Creek (Dr. Don Bliss) showed that of 281 cows tested over a season, 39% were worm negative. A study in Georgia found 30% of lambs were naturally resistant and did not need to be dewormed.
Animals that show resistance should be put into the breeding flock, those that show parasite load under the same management can be culled. For the Georgia research flock the following parameters were used to determine what animals would be culled:
" if a ewe showed strong enough symptoms of parasites that
she needed to be treated she would be culled.
Sheep brought from western US have little or no resistance to parasites, because of low parasite pressure due to dry and cool conditions. If importing sheep from the west, they will have to go through a period of resistance development, which would be very stressful for them.
Deworm only symptomatic animals. Withold feed for 24 hours before deworming- this slows the gut down and allows better adsorbtion of the worming material. Move animals to a clean pasture 24 hours after giving a dewormer.
Key treatment times: youngstock should be treated in fall if exposed to pasture. If you have tested a heavy load, treat a second time 3-4 weeks later. Also treat adults before they come off of pasture for the winter. Treat two to four weeks pre-lambing or pre-freshening in spring. Hormonal changes in the ewe or cow will stimulate hypobiotic larvae that have over-wintered in the animal to come out of their dormant stage and begin shedding eggs. Some choose to treat before animals go out into spring pasture, to ensure that animals are not bringing overwintered larvae back out into clean ground.
Build up immune system: overall immunity will vary a lot, dependent on age, cleanliness of environment, nutrition. Improve immune system through quality nutrition, vaccinations, supplements, reduce stress level.
Garlic- A study done in Maine suggests that garlic juice reduces the number of H. Controtus and coccidia in sheep fecal samples. 1 tsp of garlic juice was given per sheep once in the fall when they were brought out of the pasture and again in the spring at lambing. Adult ewes were treated again before they were put out on pasture. Garlic presumably works by making the intestinal tract healthier and more resistant to parasite infestation.
There are herbal formulas that have been developed as alternative dewormers. These may contain wormwood, epizoti, basil, gentian, or other herbs and must be used according to manufacturer instructions. Some of these products have not been tested for use on animals and may not only be difficult to get, but must be used with caution.
Pumpkin seed has been used by Native Americans to eliminate worms. There is experimentation being done on its effect as an animal de-wormer.
How to test for parasites
This counting method is based on the fact that parasite eggs will
sink in water, but will float in various chemical solutions that
are more dense than water.
Procedure: collect fecal sample from each animal. You may follow them in the pasture and wait for them to defecate, collect while they are moving through a chute, or go into the rectum with a gloved hand a remove a small amount of feces. Keep all specimens separate. If you will not use samples right away, keep refrigerated. Eggs will develop and hatch (and thus not be counted) if samples are kept for more than 12 to 24 hours at room temperature.
Measure out a consistent amount of feces for each sample (estimate the size of one sheep fecal pellet, as close to 2 grams as possible. Consider weighing the first few times, and find a small spoon or other item that will help you get a consistent amount for each sample.) Mix 1 cup sugar or salt with 1 cup clean water. Stir or shake well, till dissolved.
Mush fecal sample into small covered jar. Add to it 50 ml (1/8 cup) salt or sugar solution and shake very well until feces are well distributed in solution. Before the mix begins to separate, quickly fill a clean film canister with the solution, until very full and the solution slightly bulges on top. Place a clean glass microscope slide over the canister. Let sit 5 minutes. The eggs will float to the top and stick to the glass slide. Turn the glass slide over and place in microscope view finder.
Count every egg you see in the microscope field of view at 10x. Move the slide and count again, repeat this until you have 10 readings on the same slide. Take an average of all 10 counts for your final reading for that sample. Keep notes with animal name or number and date. Repeat several more times in a year to track parasite load.
For a more exact count, you may purchase a McMasters egg counting slide, which may be purchased from Chalex Corporation, 5004 228th Ave, S.E., Issaquah, WA 98029. www.vetslides.com (Chalex offers an entire kit, with test tubes, slides, instructions and a carrying case for $50.)
A high egg fecal count may not mean that there is a high FAMCHA score. Resistant animals can have high egg counts and not show symptoms. These are the animals you want to keep, as they have a natural ability to carry the parasite load.
A research report from the University of Aberdeen, Scotland, summarizes
what they learned about parasites this way: Controlling internal
parasites in sheep needs integrated animal health care, combining
prevention and disease diagnosis with treatment. In order to achieve
long term control the inter-dependence between soil, plant and animal
should be considered. An animal's health and its ability to resist
parasites depends on the quality of what it eats, and the quality
of what is eaten results from how the soil is managed. Let us explore each of the issues involved in successfully managing
parasites in an organic system.
Jody Padgham has been with MOSES since 2002. She is the organization's Financial Manager, the editor of the Organic Broadcaster newspaper and co-coordinator of the Organic University. Jody raises poultry and sheep organically on a 60-acre farm in west-central Wisconsin.Return to TOP