University of Vermont

Pasture Research at the University of Vermont

Managing Parasites of Grazing Livestock on Organic Farms
Bill Murphy, Ruth Shepherd, Ken Shepherd, Willow Smart, Dave Phinney, Henry Forgues, Travis Forgues, Lisa McCrory, Joanne Knapp, and Gil Myers

Most pasture-based dairy farmers change from raising calves indoors or in outdoor hutches to raising them in groups on well-managed pasture. They do this to decrease labor demand and feeding costs, and to develop animals that use pasture forage efficiently and perform well in a grazing herd. Raising calves on pasture, however, requires management of parasites. Lambs traditionally have been raised on pasture, so this problem is not new to sheep farmers.

All farmers have to control pests (e.g. weeds, parasites, diseases, flies) in their crops and livestock. Organic farmers have to
manage pests using only cultural (e.g. grazing and nutrition management,herbs, homeopathy) practices.  Pasture-based farmers generally do not have a problem with weeds because proper grazing management controls them in pastureland, and most stop producing corn and other tilled crops where weeds primarily occur, because they realize that tilled crops are not as profitable as permanent, well-managed pastureland (Cramer, 1990).

Some level of internal parasites exists in all grazing livestock. Low numbers of parasites dont cause a problem and are needed to develop and maintain animals immunity to reinfection after their first year of life. High numbers of parasites, however, consume large amounts of nutrients, directly reducing animal weight gains and milk production.  Infected animals often have rough coats and scours, and appear unthrifty. If the parasite load is too heavy, animals can die.

Indirect losses due to parasites can be more costly than direct losses of weight gain and production. Wormy mother animals produce less milk, so their nursing offspring grow slower. Infected kids, lambs, and heifers mature later and may be difficult to breed or get to market weight. Even more costly, large numbers of parasites can weaken livestock immune systems, making them more susceptible to disease (Kidd, 1993; Myers, 1988).

Five management practices support cultural and synthetic methods of managing internal parasites  in grazing livestock:
1.  Whenever possible, young (less than 1 year old) animals should graze pasture that was not grazed by the same species of animal in the previous year, so that initial levels of parasites are low at the beginning of the grazing season (Myers, 1988).
2.  Young animals should not be forced to graze close to the ground or near dung, because the highest concentration of parasite larvae are in those locations. Young animals can graze high on the pasture sward, followed by older animals that have developed immunity to graze the sward down as needed (Kidd, 1993).
3.  Moving animals every day to fresh pasture prevents them from grazing too closely to dung and removes them from dunged areas that attract flies.
4.  Graze multiple animal species whose parasites are not mutually infective.
5.  Good nutrition helps animals resist parasites and disease, so clean drinking water and salt with trace minerals including selenium (deficient in NE soils) must be available to grazing livestock at all times.

Two approaches currently exist for decreasing parasite levels in young stock:
1. Strategic deworming: young animals are dewormed with chemicals or herbs at strategic times in the parasites infective cycle, usually at 3-4 and 6-8 weeks after turnout on pasture. It is not a good idea to deworm more frequently because it is expensive and can develop resistant strains of parasites (Bliss, 1994; Kidd, 1993; Kunkel et al., 1983; Myers, 1988).

2. Contamination reduction: decrease parasite contamination of pasture grazed by young stock, thereby reducing the level of infection encountered by these animals (Donald et al., 1997).

Since the most promising herbal worming methods  (de Bairacli Levy, 1984; Lust, 1974) for managing parasitic roundworms are to treat animals with garlic or wormwood, these were the first treatments that we tried in 1998 with Ruth Shepherds sheep under management-intensive grazing. We formed 10 groups of three similar (by breed, singles, twins)lambs each, and randomly applied treatments of control, garlic (2 cloves/lamb), and wormwood (two 340-gram capsules/lamb) at 4 and 8 weeks after turnout on pasture. We weighed the lambs each month and analyzed fecal samples for parasite egg content.

Neither herbal wormer was able to counteract the apparently high level of parasite contamination of the pasture. There was no difference in lamb weight gain or fecal parasite egg level (150-200 eggs/gram) due to treatment. Lambs had to be treated with chemical wormer to keep them growing and save some of their lives.

Herbal wormers may be helpful when used with other management practices that reduce parasite contamination of pastureland. On Ruth's farm, lambs had to closely graze pasture that recently had been grazed by sheep,so parasite contamination most likely was high. By renting neighboring land this year, Ruth will graze lambs only on pasture not grazed by sheep last year.

Beginning in May or June of 1999, we will use an herbal wormer (Natures Finest, contains: garlic, onion, parsley, mustard seed, cayenne pepper, black walnut hull) to treat calves at strategic times on the Forgues farm. We will weigh the calves and monitor fecal egg counts monthly to determine if the treatment is effective.

New Zealand research (Donaldson et al., 1997) recently showed that high protein supplementation (about 1 lb total crude protein/ewe/day) around lambing time counteracted the breakdown in resistance to parasite infection in ewes at lambing, thereby reducing output of parasite eggs by ewes. Building upon this information, we have started an experiment with Ruth Shepherds sheep using expeller soy meal (48% crude protein) to provide supplemental protein. Twenty ewes were paired (by breed and age)in 10 groups. Ten receive the ration Ruth usually feeds (5 lb hay + 1 lb corn/ewe/day) and ten receive 5 lb hay, 0.25 lb corn, and 1 lb soymeal/ewe/day (energy level is the same for each group). They are being fed the high level of protein, beginning 3 weeks before lambing and continuing 1-2 weeks after lambing. Fecal samples are being collected and analyzed weekly. Fecal samples will be collected from lambs throughout the grazing season to monitor their parasite levels.

Another approach to reduce contamination is being tried this year with ewes on Willow Smart and Dave Phinneys farm. Beginning 2 weeks (March 22) before lambing and continuing 1-2 weeks after lambing, four ewes are being fed an herbal wormer (Natures Finest). These were paired by breed and age with four control ewes fed the usual ration without the wormer. Fecal samples are being collected from all of the ewes and analyzed weekly. Fecal samples will be collected from lambs throughout the grazing season to monitor parasite levels.

Literature cited
Bliss, D.H. 1994. The Cattle Producers Handbook for Strategic Parasite Control. Hoechst-Roussel Agri-Vet Co., Somerville, New Jersey. 17 p.

Cramer, C. 1990. Grass Farming Beats Corn! The New Farm. Sept/Oct. p.10-16.

de Bairacli Levy, J. 1984. The Complete Herbal Handbook for Farm and Stable. Faber and Faber, Boston. 383 p.

Donaldson, J., M.F.J. Van Houtert, and A.R. Sykes. 1997. The effect of protein supply on the periparturient parasite status off the mature ewe. Proceedings New Zealand Society Animal Production. 57:186-189.

Kidd, R. 1993. Roundup Roundworms. The New Farm. Feb. p. 6-8.

Kunkel, J.R., W.M. Murphy, D. Rogers, and D.T. Dugdale. 1983. Seasonal control of gastrointestinal parasites among dairy heifers. Bovine Practitioner. 18:54-57.

Lust, J. 1974. The Herb Book.  Bantam Books, NY. 659 p.

Myers, G.H. 1988. Strategies to control internal parasites in cattle and swine. Journal of Animal Science. 66(6):1555-1564.

Last modified December 13 2005 10:02 AM

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