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March 19, 2018
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"Food is an important part of a balanced diet." - Fran Liebowitz
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Maine Organic Farmer & Gardener
Fall 2001
Parasites
Internal Parasites and the Ecology of the Farm
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By Diane Schivera When deciding upon an approach to controlling the level of internal parasite infestation in animals, you need to manage the whole farm in a way that achieves a healthy organism. Many factors affect the severity of the situation, and any existing problem indicates that the farm is not healthy and that some part(s) of the management system or ecology of the farm needs to be altered. The health of the soil, the plants that are growing on your farm, water or moisture levels, the health and immunity levels of your animals, how animals are rotated on pastures, frequency of paddock use, the use of clean pastures, stocking rates, or the diversity of animals may need attention.
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No farm is ever totally free of parasites: They are part of the healthy organism. Consider that even in wild animals with a low infestation of internal parasites, maturation – including the age of first conception – is delayed. Although this goes against modern animal husbandry efforts of getting animals to give birth and produce as early as possible, later conception will likely increase the longevity of the animals. When soil is vital, however, the free-living larval stage of parasites (the stage that is infective) is limited. The manure harboring the parasites will decompose, and the larvae will perish within a couple of weeks. To keep the soil healthy, feed the microorganisms that feed the plants by applying a fertility source (usually manure), maintaining the proper pH, and having the mineral levels in the soil tested and adjusted according to test results. Observing plant populations in pastures can also help you determine the health of the soil. In Maine, clovers indicate a healthy soil, although they don’t prove that all is well. The presence of a variety of plant types in the pasture will encourage the health of grazing animals. Many so-called weeds are actually sources of concentrated nutrition. Pigweed, for example, has a much deeper root than grasses and will pull minerals from deep in the soil. Having a hedgerow or wilder unmown areas that the animals can graze periodically will improve their health. Browse is also important – and being higher from the ground, it is not so likely to be infective. Jerri Brunetti, who spoke at MOFGA’s Farmer to Farmer Conference in 1999, advocates these practices. He listed plants that benefited animal health – including helping with parasite control. Wormwood, other artemisias and mustards are the first to be considered for planting, but simply allowing native species to be grazed will be beneficial. Remember: Don’t allow these areas to be overgrazed; trees are especially susceptible to overgrazing. Deciding if an animal has parasites, or worms as they are generally called, is not always easy. Obvious symptoms include a rough hair coat; slow weight gain; thin, sunken eyes; diarrhea; listless attitude; and standing hunched up, indicating a painful gut. Occasionally a healthy young animal will just die, although this is rare. Parasites get no benefit from killing their hosts.
Checking a fecal sample is another way to look for parasites, although it is not foolproof. Try to do fecal exams at the same time each year. Parasite activity is greatest when the animals are in a state of change – of season, location, or activity (e.g., last month of gestation, first month of lactation). These are the best times to do an exam. The test will only give you an idea of the parasite load an animal is carrying. If you do a herd test of a mix of many animals, you will know the level of contamination in your fields, and this will be a great help in deciding upon your grazing strategy. Many factors must be considered when planning how to manage pasture. The most important one relative to parasite control is that young animals are the most susceptible to parasite infestation. When they have worms, they also pass the most eggs, so regrazing a pasture with young stock more than once in the same season is a bad practice, while putting all young stock on clean pastures is good. Clean pastures are those that have not been grazed for at least a year by the same species or that have been grazed only by mature animals. Rotating sheep and goats with cattle is helpful, because only a few parasites infect both species. Contamination in a pasture can also be reduced by haying the field, especially if it is mowed closely and when the grass is damp. Opinions vary as to whether harrowing the pasture helps; harrowing does drag eggs around, but it also exposes them more to weathering. A good plan for sheep would be to turn the flock onto a clean pasture at six weeks post lambing. The ewes will be depositing fewer eggs, and the lambs will be starting to graze seriously. Heifers can be slowly immunized by allowing them to graze in a clean pasture with a few dry cows who will be a source of infection. This immunization process is important. Healthy young animals will develop an immunity to parasites if they are introduced to them gradually. Animal density on the pasture affects the spread of parasites. “For a given parcel of land, parasite infestations are four times greater where animal density is doubled,” according to “The Control of Internal Parasites in Ruminants,” by agronomist Jean Duval, M.S. (The paper is available at the MOFGA office.) He recommends fewer than 10 lambs /2.5 acres, although the rate will vary according to the quality of pasture. Nearly 80% of the parasite’s free-living larval stage is on the first 2.5 inches of vegetation. By restricting the animals’ grazing to 4.5 inches above the ground, infection will be reduced. However, when practicing intensive grazing, Vaughn Jones, a grazing specialist from New Zealand, recommends grazing clean pastures closer in order to expose the larvae to the sun and to drying. The species of animal also needs to be considered when deciding on the height of grazing. Sheep and goats tend to graze closer to their feces than cows, who avoid their pats. New methods of parasite prevention are being investigated as nematodes are becoming resistant the various pharmaceuticals, including the ivermectin that is allowed in organic standards. Other control methods that are being studied include trying to breed animals that resist parasites; finding fungi that will destroy parasites in the pasture; developing vaccines; and investigating herbs that will help keep the gut healthy and resistant or will eliminate infestations. Please note that this article does not address elimination of an existing parasite. If a problem exists, the species of parasite must be determined, since eradication methods are specific with some species and more general with others. This information is available by contacting the MOFGA office. About the author: Diane Schivera is MOFGA’s Technical Services Assistant. You can call her at the MOFGA office with your questions about farming and gardening.
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