Getting Started In Sustainable Animal Husbandry 

By Ron Klein

Gastrointestinal Parasites of Sheep and Goats


This is the first in a series of long promised articles dealing with livestock husbandry issues for the new farmer.  


Introduction: “So you want to raise goats eh?”


Small ruminants are often at the core of a productive and sustainable homestead or micro-farming operation.  Small ruminants-mainly sheep and goats-provide a source of nutrient dense food  for the farm family as well as potential income and barter from the production of meat, dairy products and fiber.  The purpose of this series of articles is to provide the basis for informed decisions that will result in humane and productive animal husbandry practices.


My basic premise is simple:  Work smart and not dumb.  To have a sustainable, productive and rational control of gastrointestinal parasites in animals kept in an organic or natural production system the Herdsman MUST understand the risks defined by parasite life cycles, epidemiology, pasture management, animal nutrition and breeding cycles.


Worms: Gastrointestinal Companions


The two principle internal parasites of goats and sheep in Southwestern Michigan are Haemonchus contortus (Barber pole worm) and Ostertagia sp. (stomach worms).  These two species have a significant impact on domestic goat and sheep production in our area. To understand how to deal with these parasites, the Herdsman needs to understand the life cycle of the parasite, the biology of the host animal, and more fundamentally, the co-evolution of ruminant host and parasite.  


There are two fundamental concepts we need to understand: infection and disease. An animal is considered to be infected when it hosts worms without any chronic or obvious health effects.  This definition of “infection” is similar to symbiosis or a “symbiotic relationship” where the worm needs the host to survive but its presence is not necessarily harmful to the host.  


Disease is where the host suffers a loss of condition and possible death due to a large number of worms-or a high worm burden or infection.  In any flock of sheep or herd of goats all animals could be infected with only a very small number being diseased.  Small ruminants that are infected with worms may remain productive; however productivity will be severely compromised if they become diseased.


Wild versus Domesticated


In the wild all sheep and goats are infected-the development of disease generally is associated with stress and poor nutrition. The latter can be due to environmental factors such as drought or the absence of an essential nutrient.  The patterns of behavior of wild goats and sheep limit exposure and reinfection by worms.  In the wild goats and sheep evolved in and now generally inhabit hilly and mountainous areas.  They freshen during the spring with access to lush pasture and browse and follow the browse line to higher elevations as the season progresses.  As winter approaches, the grazing patterns reverse and they return to lower elevations; a cycle that occurs over the course of 5-7 months.  This pattern minimizes exposure to manure contaminated pasture and infectious worm larvae-diminishing the probability of their obtaining a high level of infection resulting in disease.  Grass based or pasture based livestock operations mimic these behavior patterns using Managed Intensive Grazing (MiG) systems.


Domesticated sheep and goats do not have the opportunity to avoid manure contaminated pasture and feed.  This is due to confinement, limited grazing or browse, or being forced to spend too much time in one area of pasture.  In addition, though domestic animals have a better opportunity to have superior nutrition due to supplements and trace elements not readily available in the wild, the Herdsman may not fully appreciate subtle nutritional requirements and believe that pasture and a salt block are adequate.  In addition, domestication can place a lot of stress on sheep and goats seen in multiple births and the demands of milk and wool production.  Stressed animals are more susceptible to infection resulting in disease


Another important point is immunity.  Sheep and goats need good nutrition to produce sufficient protein in the form of antibodies to control the level of worm infection.  Prolonged stress (multiple births, demands for high level milk production) depress the animal’s immune system in general. In adult dairy goats, the impact of gastrointestinal parasites is greatest during pregnancy, just before and during freshening, and in early lactation.  This period is known as the peripatrum and it is then that periparturient relaxation (depression) of immunity occurs. Adult dairy goats are more susceptible to disease and vulnerable to parasite infection.  The animals must be in peak health going into this period. Immunity to parasitic worms occurs when low numbers of worms are ingested over time.  Effective immunity will not develop if the animal is stressed and ingests large quantities of infective larvae.  In fact, the animal’s natural defense will be overwhelmed and the transition from infection to disease will be rapid.


The digestive system of small ruminants


I find that the evolution of ruminants to be wondrous and amazing thing.  The co evolution of the harvester of plant matter and the dynamic rumen microflora community of bacteria, yeast, fungi and protozoa that digest and process those plants is a fascinating symbiosis. Ruminants ingest materials monogastric (single stomach animals) cannot use as a food source-these materials are broken down by the microflora into soluble nutrients and utilized by the animal—including the very organisms that digest the harvested plants!


The digestive system of the goat or sheep is divided into a series of compartments, basically the reticulum, rumen, omasum and abomasum. (I’ll be discussing applied rumen anatomy in the second article of this series).  The reticulum and rumen are essentially bacterial fermentation systems that along with fungi, yeast and protozoa break down the main constituents of fodder (soluble nutrients, cellulose and fiber).  The rumen contents are flushed into the omasum where they are further broken down and the resultant nutrients then enter the abomasum where they are further digested and later absorbed in the small and large intestines. Up to 90% of the protein utilized by sheep and goats is actually the very bacteria grown in the rumen.  It is extremely important to understand this-since in general- we feed the rumen microflora which in turn feed the animal


The abomasum is the true stomach of the ruminant-just like ours-it secretes acids and enzymes that break down foods producing absorbable nutrients.  The abomasum is home to parasitic worms.


The Main Parasitic Worms



Haemonchus contortus-the Barber pole worm.  These worms have a twisted form with alternative bands of red and white, they are the thickness of dental floss and range from .5 to 1.2 inches in length.  They cut into the stomach lining into blood vessels where they suck blood.  The worms move from site to site as they feed-and the wounds remain open and continue to bleed.  In heavy infections blood loss can be very rapid.  The host becomes anemic-and because of the loss of blood tries harder and harder to breathe to replenish lost oxygen- disease presentation is very similar to pneumonia and is often misdiagnosed with tragic results. The small blood vessels around the eye go from pink to pale to snow white; bottle jaw can develop, and because of internal GI bleeding feces appear tarry and black.  


Ostertagia sp.-stomach worm.  These worms are about half the size of Haemonchus.  Ostertagia sp. feed by burrowing into the lining of the stomach blocking the release of hydrochloric acid.  The lining of the stomach is damaged; the pH changes to less acidic and critical digestive enzymes cease to function.  The worm feasts on small proteins reducing the amount of protein in the blood.  This results in fluid accumulation especially under the jaw of the animal producing swelling called “bottle jaw.”  The disruption of digestion causes severe diarrhea.  Overall, there is a loss of condition and weakening of the host.  One of the challenges the Herdsman faces is keeping older goats in good condition-this is often difficult due to the severe damage caused to the stomach lining by these parasites over the course of the host animal’s life.


Understanding the parasitic worm life cycle.


The life cycle of Haemonchus and Ostertagi are similar, and breaking the life cycle is critical to controlling rates of infection.


Adult worms living in the gut of the host lay eggs that pass out of the host in the feces.  First stage larvae-L1-develop depending on temperature and moisture.  L1 stage larvae hatch within the feces and feed on bacteria.  After a time the L1 stage larvae molt their outer cuticle (skin) and the second stage larvae-L2-emerge and continue to feed on bacteria.  L1 and L2 larvae are not infectious.   L3-third stage larvae are infectious-they do not molt but retain their outer cuticle. L3 larvae have two cuticles—the outer cuticle is a protective barrier that permits survival on pastures and even to over winter.


Timing is important.  Depending on humidity and temperature infectious L3 larvae can develop in seven to 30 days after eggs have been passed in feces.


L3 larvae climb to the moist tips of dew covered grass or under the leaves of low growing clovers where they are ingested-develop into L5 larvae and eventually to adult worms.  The adult worms start feeding and laying eggs repeating the cycle.


Hypobiosis-the curse of freshening


When L3 larvae are ingested in the fall-because of changing environmental factors as winter approaches-the larvae enter the stomach membranes.  The Larvae molt and “encyst” remaining inactive until their development is triggered by the host’s physiological changes in the spring and rising temperatures OR when the host gives birth.  After freshening, the L3 larvae emerge all at once, molt and as adults begin to feed.  Within three weeks after giving birth a heavily infected doe will become anemic, and show symptoms of pneumonia.  Once pneumonia like symptoms are noticed-from our experience-the doe will die within 24 hours.  Treating at that time with a drench to kill the parasites may be of no avail-the worms will die but the stomach lining will continue to bleed. In our experience, treatment needs to be a slow release of dewormer given by injection subQ-and a race against time to save the animal. Remember-this is a time during the does immune system is naturally “relaxed.”  It is important that does coming off pasture in the fall either have a very low worm burden or are treated with an effective antiparasitic drug BEFORE L3 larvae go hypobiotic. Once the larvae go hypobiotic they are not susceptible to any form of treatment.



Controlling Worms


Grazing Control


The conceptual basis of controlled grazing is simple -the higher number of infective larvae that are ingested the higher the number of worms in the host and the higher the probability of disease.  The goal of the Herdsman is to understand and exploit factors that drop the number of eggs and worms his animals are exposed to. Controlled grazing needs to mimic the grazing patterns of wild goats and sheep.

  1. Worm egg development is highest at temperatures between 50-80 F.  At the higher temperatures larvae will develop within three days-but there is a high mortality dropping the number that actually reaches an infectious stage.  Our average summer temperature range (early and later summer) is between 60-70F, within this range the majority of infective larvae will develop AFTER 14 days.  A Herdsman who moves his flock or herd off contaminated pasture within two weeks after initiating grazing will greatly diminish exposure to infective larvae.
  1. Worms increasingly die at temperatures below 40F.  Pastures free of snow where surface temperature can shift above and below freezing will have increased larvae mortality.  A layer of snow can provide protection and increase larvae survival.
  1. Humidity is vital for infective stage larvae survival.  All larvae stages are susceptible to desiccation which is the main factor in blocking development into infectious larvae.  Rainfall and dew increase the number of infectious larvae.  Moisture is critical for the larvae to move away from feces and onto grass.  Careful examination of an infected pasture will show thread like larvae in drops of dew on the tips of low growing grass! Moisture is also critical to break down feces to release larvae.
  1. Dried feces can be a problem.  The pellets of goat feces have a hard dry outer coat that reduces evaporation protecting the larvae inside.  Fecal pellets-even in hot and dry conditions can still harbor viable larvae.
  1. The condition of pasture is important.  The viability of larvae are increased by microenvironments that promote high humidity and moisture.  Any matting of organic matter will diminish evaporation and promote larvae survival.  The movement of larvae onto grass tips and the underside of clovers is promoted by high moisture and the height of the plant.  Higher grazing will diminish exposure over grazing closer to the soil.  Haying or mowing promotes drying diminishing the level of infective larvae.

Nutritional factors and Forage


The over all condition and health of the host animal is extremely important.  It is critical to provide excellent nutrition (I’ll be covering this topic in a later article).  Good nutrition allows the development of resistance to worm infection and also will counteract various levels of infection.  Sheep and goats-in good condition-become increasingly resistant to infection when they ingest small numbers of infective larvae over an extended period of time.


In New Zealand studies have been conducted on the effect of various forage plants on worm infections in lambs.  For example, chicory and birdsfoot trefoil both contain some level of anti-parasitic compounds; more than most forages. In addition, providing browse and developing tree-pasture systems diminishes parasite burdens.  Controlled studies conducted in the southern United States have shown that lambs grazed on pasture rich in chicory have a significantly reduced gastrointestinal worm burden consistent with studies conducted in New Zealand.  Many attribute the “antiparasitic” compounds isolated from chickcory, birdsfoot Trefoil and various woody plants as being responsible for a diminished worm burden in grazing or browsing animals. It is important to understand that results from controlled studies using extracted natural compounds from various plants, may not necessarily translate to real world pasture grazing.


For example, extensive studies conducted on tannins-the fundamental antiparasitic compound in woody plants- have shown even when fed to small ruminants in concentrations in excess of what would be expected in a pasture, that tannins have no effect on dropping worm infection.  In fact the “antiparasitic” effect seen in the real world may be due to diminished exposure to L3 larvae because of the structure and height of various plants.  This includes chicory and birdsfoot trefoil.  This is not to say that compounds in natural graze or browse do not have some effect  but rather that the effect is far less than claimed in common lore.  


New Potential biological control?


The fungus, Duddingtonia flagrans feeds on free living parasite larvae in pasture.  Studies conducted in New Zealand, India, and Sweden have shown that feeding sheep and goats the spores of this fungus greatly reduces infective larvae on pasture.


Measuring infections


The Herdsman should know the level of infection in his herd or flock and identify those animals that may be the primary carriers of infective worms.  Usually a small number of animals is responsible for >80% of the infective larvae the herd or flock are exposed to.  It is critical to identify and treat or cull those animals.  Measuring gastrointestinal parasite infections can be done in three related ways:


The first is the general conditions of the flock or herd.  In this case, the Herdsman knows the condition of his animals; he looks for such things as a lack of vigor, bristle like hair or loose wool, development of bootlejaw, diarrhea, signs of pneumonia, and most important-anemia.  Anemia most easily recognized by the condition of the membranes around the eyes—normally pink with clearly defined red blood vessels-but if heavily infected the membranes become increasingly white or pale, and the blood vessels are very difficult to see.  The Herdsman needs to be on top of his game since death can quickly follow a presentation of severe anemia, pneumonia or bottle jaw.


The second is doing fecal egg counts (FEC):  FECs can be done on individual animals of groups of animals.  The Herdsman can do FECs for a small investment.  Protocols and procedure as well as descriptions of home-made equipment and kits can be found at various websites referenced at the end of this article. The procedures are simple and there are any excellent references available to aid in identification of worm eggs in fecal samples.


The third is post mortem examination of sacrificed animals.  Many producers routinely examine the abomasums of animal slaughtered for meat.  The lining of the abomasum needs to be carefully examined-looking for reddish thread like projections.  A heavy infection will reveal a sheet of worms.  Some large producers run wethers with their dairy does both for meat production and as indicators of the worm burden of the herd.


Treatment


There are available drugs that are still effective against Haemonchus and Ostertagia if used strategically and if your animals do not have a large population of drug resistant worms.  The three classes of drugs are the benzimidazoles (fenbendazole), imidathizoles (morantel) and the macrocyclic lactones (ivermectin).  Because of the problem of over use selecting for resistant worms there are limitations using these compounds.  One important point to make is that at no time should the use of these drugs substitute for effective animal husbandry practices.


If chemical intervention is necessary we recommend the following:

  1. Only treat infected animals that show signs of disease.
  2. If possible, conduct FECs before treatment.
  3. Do the treatment only on animals whose food has been withheld to increase efficacy of the drug.
  4. Only use the recommended dose.
  5. IF you suspect a worm bloom three weeks after freshening-do not drench-but administer treatment by injection subQ.  The slower death rate of feeding worms will decrease the probability of the doe bleeding out.  Please note that this is not the commonly recommended practice.

Thoughts on Popular Non-chemical Treatments



I have talked with many producers about popular non-chemical treatments including Shaklee’s-H soap, diatomaceous earth, wormwood, garlic, neem oil, etc..  Aside from anecdotal comments (“This has been used in my country for a thousand years…..”), there is sparse to no data supporting that these treatments have any beneficial effect in reducing worm infections. And herein lies the danger of a Herdsman killing animals with kindness.  Prophylactic treatment with soaps, diatomaceous earth, garlic and similar methods afford no protection and can lull the Herdsman into a false sense of security assuming his animals are “healthy.”  Despite the vacuous basis for these treatments this is not to say that organic management methods are not effective in dealing with gastrointestinal nematodes.  For example, studies conducted in Brazil, for example, compared the worm burdens of goat herds from conventional versus organic farms.  Those studies are worth noting.


Scientists in Brazil studied parasite burdens in Saanen dairy goats maintained on a variety of conventional and organic dairies.  The conventional farms used continuous grazing on the same pastures (no rotation) with monthly application of standard antiparasitic drugs.  The organic farms used rotational grazing and separated animals based on age.  Goats on organic farms had higher fecal egg counts, more clinical presentation and a higher rate of pasture infectivity during peripatrum.  However, the conventional farms-even with monthly deworming-animals were still moderately infected raising the specter of selecting for drug resistant worms.   Even though the organic farms did have slightly higher rates of infection-the level was considered moderate and indicated with proper and more intense management that worm levels could be controlled. In our work at Pharmacia Animal Health we discovered that even without exposure to drugs, sheep herds we tested throughout the world had small sub-populations of benzimidazole (Panacur etc..) drug resistant worms.  The worm genome is very plastic, subject to constant mutation and the worm populations are large-misapplication of drugs will select for a preexisting population of resistant worms.  It is important to understand that the application of antiparasitic drugs does not create drug resistance-but rather- favors the survival and proliferation of small numbers of worms already resistant.  This must be appreciated by the Herdsman.


We have had personal experience in dealing with diseased animals treated by friends and neighbors exclusively using “alternative” methods. Their animals usually were thought to be healthy, but if you know what to look for, were anemic or misdiagnosed with pneumonia, milk fever, or missing some trace element in the feed. Several died.


What do we recommend?


We currently have forty milking does and 25 dairy water buffalo. Our goal is to do our best to mimic the ruminant-parasite relationship found in the wild and approach a more symbiotic relationship between host and parasite.  To accomplish this we need to reduce exposure, assure animal health and break the parasite life cycle. We know we cannot kill all worms nor establish a sanitized and sterile unnatural environment.  We need to learn to live with worms.

  1. Managed intensive grazing.  Rotate animals to new pasture a maximum of every 10-14 days.  This diminishes exposure to infective larvae, allows the animals to graze pasture in a vegetative state with higher nutritional content promoting better health.  There are very cost effective technologies available such as light weight electric cross fencing or portable netting used for mobile divisional fencing.
  1. Multispecies grazing.  Since parasitic worms are very species specific, graze goats or sheep, followed by cattle, horses or poultry (we prefer turkeys and muscovey ducks).  We graze our milking does (and sometimes calves together), followed by the dairy water buffalo.  The buffalo are close grazers and essentially a larvae clean up crew.
  1. Allow sheep and goats access to browse if possible.
  1. Be certain that the flock or herd has good nutrition.  More on this later, but to ensure efficient forage utilization throughout the year ruminant health is vital.  We supplement with a new loose mineral formulated with the help of a nutritionist and available at Southwestern Michigan Feed in Lawrence Michigan (ask for the goat mineral we use), and a mineral tub (such as Crystalyx HE-10%).  No matter how wonderful the pasture may look -herd health will always be limited by a missing essential nutrient.
  1. Walk among your herd or flock daily-note their condition and check the texture of their hair or wool, look for anemia or abnormal stools.  The Herdsman must know his animals.
  1. Do fecal egg counts on selective animals, and if necessary treat accordingly with the intelligent use of know effective anti-parasitic drugs. Do not fall victim to popular notions about parasite control without asking the simple question:”How do you know X really works?”  If the answer does not include fecal egg counts done before AND after treatment-be cautious.  Herd health could be do to rotational grazing for example and have nothing to do with the administration of treatment.  Translating someone else’s apparent success to the specific conditions on you farm could be tragic.
  1. Maintain a closed herd.  Treat and quarantine new animals for 21 days.
  1. Implement a biosecurity program.   Sounds fancy—but it is simple. People visiting your farm who have had contact with animals on another farm-have them wash their hands and clean their boots.  You need to intelligently avoid introducing new diseases do not be casual about herd health.

By understanding the life cycle of parasitic worms, the biology of sheep and goats and the behavior of wild sheep and goats you can devise an intelligent and rational “natural” strategy appropriate for your farm.  As a responsible Herdsman you will need to interact closely with your animals, understand their nature and requirements at a high level of awareness.  Remember, the goal is to have healthy and productive animals raised in a sustainable and humane manner.


References:

There are many good references on the internet—I cite just a few.



Basic references


Managing Internal Parasites in Sheep and Goats, from ATTRA (2006) available at https://attra.ncat.org/attra-pub/summaries/summary.php?pub=215

The control of internal parasites in ruminants.  J. Duval, Ecological Agriculture Projects, McGill University available at: http://eap.mcgill.ca/agrobio/ab370-04e.htm

Living with Worms, Peter Stockdale, from the Canadian Organic Growers series of Practical Skills Handbooks, (2008)   excellent introduction available at www.cog.ca

Molly Nolte has put together one of the most valuable and easily accessible
website on goat husbandry. She includes instructions for doing fecal exams and where to find equipment all at a reasonable cost.  http://www.fiascofarm.com/goats/index.htm   


Managed Intensive Grazing References


Greener Pasture on Your Side of the Fence: Better Farming through Voisin Management-Intensive Grazing.  Bill Murphy  (a must read for pasture based producers)

Grass Productivity    Andre Voisin (classic)

Grass Fed-Cattle   Julius Ruechel (general principles apply to sheep and goats)


Veterinary books from our reference shelf dealing with goats


The Goat keeper’s Veterinary Book    Peter Dunn

Goat Medicine   Mary C. Smith and David M. Sherman  Mary C. Smith (Author) Visit Amazon's Mary C. Smith Page  Find all the books, read about the author, and more.

Sheep and Goat Medicine  David Pugh

Diseases of the Goat  John G. Matthews


Veterinary Clinical Parasitology, 7th  edition  Anne Zajac and Gary Conboy  excellent for identifying all types of important  parasites when doing fecal examinations.


A Few Scientific papers and studies.


Biological Control of Helminth Parasites by Predatory Fungi, ( 2009), S. Dejat and P. K. Sanyal,  On Line Veterinary Journal, Vol. 4 No. 1, Article 31 available at  http://www.vetscan.co.in/v4n1/biological_control_of_helminth_parasites_by_predatory_fungi.htm

Biological Control of Nematode Parasites of Small Ruminants in Asia (2002), Final Proceedings of FAO Technical Cooperation Project in Malaysia available at:
http://cnia.inta.gov.ar/helminto/pdf%20alternativos/FAO_TCP_MAL_0065(T)1.pdf

Biological control of nematode parasites in sheep. (2006), M. Larsen, Journal of Animal Science, 84:E133-139.

Dynamics of gastrointestinal parasitoses in goats kept in organic and conventional production systems in Brazil  (2011)  J.B. Silva, G.M Fagundes and A.H. Fonseca, Small ruminant Res.  98: 35-38

Effect of plant species on the larvae of gastrointestinal worms which parasitize sheep (1998) Niezen, J.H., et al., International Journal of Parasitology p. 791-803

Evaluation of biological control of sheep parasites using Duddingtonia flagrans under commercial farming conditions on the island of Gotland, Sweden,  P.J. Waller, et al., Veterinary Parasitology, Volume 126, Issue 3, 15 December 2004, Pages 299-315

Genetic Variability of the β-Tubulin Genes in Benzimidazole-Susceptible and -Resistant Strains of Haemonchus Contortus R. N. Beech, R. K. Prichard, and M. E. Scott,  Genetics. 1994 September; 138(1): 103–110.

Haemonchosis on organic farms. (2006)  J. Van Dijk and E. Morgan , Veterinary Record 159: 642

Nematode control in “green” ruminant production systems. (2004), Waller, P.J. and S.M. Thamsborg, Trends in Parasitology, 20:493-497.

Parasitological examinations in sheep health management. (2010) M.A. Taylor, Small Ruminant Res. 92:120-126

Tannin rich peanut skins lack anthelminthic properties. (2011)  C.T. MacKown, M.A. Brown and E.L.Walker, Small ruminant Res. 96:195-200

The effect of forage species on performance and gastrointestinal nematode infection in lambs.  (2011) M.C. Miller, S.K. Duckett and J. G. Andrae.  Small Ruminant Res. 95: 188-192

Ron Klein 2011





Ron and Suzanne Klein own and operate Windshadow Farm & Dairy in Bangor, Michigan, a certified Grade A dairy.  They milk over 40 dairy goats and have a herd of 24 dairy water buffalo.  In cooperation with Evergreen Lane Creamery in Fennville, Michigan, the milk is made into soft and hard cheese, and a wonderful water buffalo milk camembert (all available throughout West Michigan). Ron is a member of the Wisconsin Dairy Goat Society, American Dairy Goat Association and International Goat Association as well as the American Veterinary Parasitology Association, Michigan Bar Association,  and American Society for Microbiology. Ron is a retired Senior Scientist who studied fermentation yeast biology and the molecular biology of small ruminant parasites. Ron and Suzanne are also attorneys.  Suzanne practices Federal criminal defense and general agricultural law, and is on the Board of Directors of the Southwest Michigan Land Conservancy; both are active members of the  Farm to Consumer Legal Defense Fund, and on the  Board of  Michigan Land Trustees.




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