Infection with parasites, especially those of the gastrointestinal tract can, and in some circumstances do, cause substantial losses to goat owners. These range from decreased utilization of feed in unthrifty animals to death. The most important of the gastrointestinal parasites include roundworms and coccidia. An effective control of these two groups of parasites will make a significant contribution to your goats's health and well-being.
Eradication of these parasites is impossible, but the simple presence of a parasite in an animal does not indicate disease. An animal will show the symptoms of disease only when parasite loads become excessive or when an animal's natural immunity to disease becomes suppressed. A certain amount of understanding about the life cycle of these parasites is necessary to control them most effectively using anthelmintics or other means of parasite control.
Of the family of roundworms, the really important ones are the barber pole worm (Haemonchus contortus) and the brown stomach worm (Ostertagia circumcincta). The barber pole worm is by far the most significant parasite in this region of the country. According to the Rollins Animal Disease Diagnostic Laboratory in Raleigh, autopsies performed on goats indicate that barber pole worms are the most prevalent cause of goat deaths. Other species can and occasionally do cause economic loss to goat producers but they are of lesser significance compared to the barber pole worm.
As a bloodsucking parasite the barber pole worm causes anemia. One thousand barber pole worm larvae can suck up to 800 cc of blood per day. The prime symptom, along with blood loss and gut damage, anemia can be detected as paleness around the eyes, inside the mouth, or inside the edge of the rectum or vagina. You may also detect swelling under the jaw (bottle jaw) or low on the abdomen. Diarrhea may occur but sometimes the goat dies before diarrhea can develop. Other symptoms include loss of weight, poor growth, unthriftiness, and a marked decrease in milk production.
The facts about the life cycle of which are important to understand are the following:
1. Adult female barber pole larvae have a tremendous egg laying potential (5,000 to 10,000 eggs or more per day) . Eggs are passed in the feces and contaminate the environment.
2. Eggs hatch and pass through three larval stages, the third being infective for the next host when ingested.
3 . The successful development of these stages outside the host depend on the climate. Barber pole eggs and larvae love warm, moist conditions and hate cold or very hot, dry conditions
4. Barber pole larvae can also undergo a process called ARRESTED DEVELOPMENT where they sit quietly in the abomasum (the true stomach of ruminants) following infection and don't become adults until several months later. This is an important adaptation for keeping the worm around through cold winters when eggs and larvae don't survive well on pasture. As a result, we see an increase in parasite transmission from spring to fall.
5. The worms require about three weeks to complete their life cycle. However, if large numbers of larvae are inactive and lying in the lining of the stomach and intestines, severe parasitism can occur within 7 to 10 days after deworming.
6 . Diagnosis is made on symptoms and identification of worm eggs under a microscope. At NCSU, animals are dewormed when the number of nematode eggs per gram of feces reaches 600 to 700.
Little change has occurred in recent years in the dewormers that are licensed for use in goats. Considering only the "modern dewormers" which are effective against a number of species and have high safety margin, there is only 1: thiabendazole. In general, the efficacy of this product is regarded as low. Several other products have been shown to have efficacy against barber pole worm and other members of the same family in experimental situations (see Tables 1,2,3).
Other benzimidazoles (drugs in the same family as thiabendazole, i.e. fenbendazole, oxfendazole, albendazole) . There is evidence indicating that goats metabolize this group of drugs differently and require higher doses than sheep (2 times the sheep dose) as a result. Also, oxfendazole and albendazole have been associated with problems in pregnant sheep. Doses that have been used in sheep include: fenbendazole, 5-10 mg/kg; oxfendazole, 5 mg/kg; albendazole, 5 mg/kg.
When a worm becomes resistant to one product in this group it becomes resistant to all of them. Resistance to benzimidazoles is widespread in barber pole worms and once it occurs it will stay around for years whether you continue to use the drugs or not.
Levamisole is another widely used deworming product for ruminants. In goats, it is usually used at the sheep dose (8 mg/kg or 3.6 mg/lb). Again, goats need a higher dose than the sheep dose and 11 mg/kg (5 mg/lb) has been recommended. The safety margin for this product is lower than for the other anthelmintics and side effects, especially salivation, may be seen after treatment especially if the injectable form is used. The oral form is safer and will be eliminated from the animal faster. Barber pole worms resistant to levamisole have been documented, although resistance to this product does not appear to be as widespread as benzimidazole resistance.
Ivermectin is available as an injectable product for cattle and a drench for sheep (0.2 mg/kg or .09 mg/lb). Experimentally, the oral form appears to be more effective than the injectable, especially in goats. The withdrawal time is also shorter when the product is given orally.
Morantel is a product which chemically is very similar to pyrantel, which is the active compound found in the Strongid® horse dewormers. Morantel is currently marketed for cattle (Nematel and Rumatel®) and is useful because it has no milk withdrawal time. Research has been done with goats and this product appears to be effective (4.5 mg/lb or 9.9 mg/kg) and not have milk residues. Formulations of this drug for administration in feed are available for other species.
It is difficult to stress too much the importance of minimizing the development of drug resistance. Once these products lose their efficacy, there isn't really much on the horizon to replace them. An Australian educational program to help reduce the development of resistance suggests the following steps that owners can take. The acronym of the program is especially appropriate!
Check for resistance
If you suspect that a dewormer is not working it is possible to check for resistance by doing a fecal parasite egg count before and after treatment.
Reduce the frequency of exposure to dewormers.
The more frequently the worms are exposed to a drug, the more likely it is that resistance will develop. Because Haemonchus has a slightly shorter generation time than other members of its family and because females produce huge numbers of eggs, parasite populations can increase to dangerous levels in very short periods of time and many owners rely on frequent treatments. Reducing treatments by incorporating pasture management techniques into your control programs is a practical way to limit use of dewormers.
Annually rotate dewormers.
It is not a good idea to use the same dewormer year after year. The best interval for switching dewormers is still a bit controversial, but most parasitologists now agree that annually is probably best.
Check the dose.
It is very easy to underdose animals. Even experienced owners may underestimate average weights. Always dose groups of animals for the heaviest, not the average goat.
Keep resistance off your farm.
New goats may bring resistant parasites with them. Never mix new animals with residents without deworming them first. It has been recommended that new animals be treated with 2 times the normal dose of 2 dewormers to make sure that any resistant worms are eliminated and don' t have an opportunity to infect your pastures with eggs.
Prevention, rather than cure, is the philosophy used in developing control programs against gastrointestinal worms. It should be assumed that worms cannot be eradicated but infections can be limited to the extent that they will not cause economic loss to the producer. A combination of treatment and management are strategic use of anthelmintics. Anthelmintics are used at a time when most of the total worm population is within the host and not on the pasture, such as when livestock are moved from a contaminated pasture to a parasite free or nearly free pasture. Pastures become parasite free when they have been tilled or given prolonged rest at a suitable time of year or were grazed by animals which are not satisfactory hosts for the target parasite species.
Strategic treatments aimed at worms that have undergone arrested development, in winter or in spring kidding females, have proven effective in controlling worm burdens during the warm weather transmission season.
Tactical treatments when weather conditions have been favorable for the transmission of parasites, eliminates worms from the gastrointestinal tract before they have the opportunity to reproduce and further contaminate the environment. The timing of tactical deworming may be based on increasing fecal egg counts. Treatment at this time, especially when accompanied by movement to parasite free pastures, may prevent an outbreak of disease.
Salvage (treatment to save lives, not control parasites) is a frequently used anthelmintic strategy in small ruminants. This is treatment in the face of a disease; the animals are frequently anemic, may have diarrhea, bottle jaw or swelling (edema) along their ventral abdomen due to blood loss from the parasites.
It can be difficult sometimes to decide whether you have worms resistant to a specific drug or whether animals are just becoming reinfected with parasites so rapidly that it appears that resistance is present. It is possible to determine if parasites are resistant using Fecal Egg Count Reduction Test (FECRT). Fecal samples are collected from goats (10% of the herd or at least 5 animals) which are then dewormed. Ten to 14 days after deworming a second sample is collected and the parasite eggs are counted again. If your dewormer is still effective you should see at least a 90% reduction in fecal egg counts. It is very important that all goats be dewormed with an accurate dose when performing the FECRT. It is also important to wait about 10 days before collecting the second sample because some drugs may still decrease egg production for several days, even when the adult worms are resistant and are not killed. By waiting 10 days, you allow egg production to come back to normal. This is not a highly sensitive test for resistance and if the results indicate that the dewormer is no longer very effective you can be assured that there is widespread resistance in the population of parasites infecting your goats.
In any herd, certain animals are less resistant than others to gastrointestinal parasites. The animals prone to have heavy parasite loads should be culled because a) they are most likely to pass that trait on to their offsprings and b) they will shed more nematode eggs through their excreta, therefore increasing the worm population of their surroundings. In addition, culling these animals is the first step toward the development of a herd that will have a higher degree of natural resistance to parasites.
One of the best ingredients of a parasite control program is reducing the number of parasites that the goats are exposed to in the first place. One way to accomplish this is to manage your pasture in a way that will reduce its parasite load. There are several ways to do this:
Take a hay crop or plow and reseed. This type of pasture can be incorporated into a dose and move program in which goats are grazed on one pasture in the early grazing season and then dewormed and moved to another goat pasture which was used for a first cutting of hay. Another move before the end of the grazing season will probably provide the best parasite control.
Graze a contaminated pasture with another species. There is only one worm species that can infect cattle, sheep, goats, pigs and horses and for practical purposes it isn't very important. When another animal species eats the goat parasite larvae they will be killed. THIS DOES NOT APPLY TO SHEEP, which goat worms find equally delectable.
Pasture Rest. Unfortunately, it takes a long time for the worm eggs and larvae to die off if the pasture is just left empty. A year or at least an entire grazing season is required. This is usually impractical and it also means that the kind of rotational grazing at short intervals used to maximize pasture production usually doesn't have much impact on parasites.
Questions and comments
Is there a relationship between worming in late gestation and abortion?
Goats seem to be more sensitive than other livestock species in terms of abortion in late lactation. Abortion cases have been reported. However, it is not clear whether or not abortion was provoked by the wormer used or simply by the stress related to animal handling and deworming.
As a general rule, be conservative!! Avoid deworming during early pregnancy if possible (first 20 to 60 days).
Some products are to be avoided. Cases of abortion have been reported, BUT NOT PROVEN, with levamisole. Albendazole should not be used in pregnant does.
The symptoms of coccidiosis can vary from some loss of appetite and slight, shortlived diarrhea to severe cases involving great amounts of dark, bloody and foul smelling diarrhea, fluid feces containing mucous and blood, straining, loss of weight, rough hair coat, with up to 15% dehydration. The primary pathology associated with coccidiosis involves intestinal cell destruction. Scarring of the intestine following treatment or recovery may result in a permanently unthrifty animal. Diagnosis is based on history, symptoms and microscopic examination.
In the presence of appropriate temperature, moisture and oxygen, coccidia eggs passed in the feces become infective in one to several days and readily contaminate food and water. Goats become infected after ingesting the eggs. However, presence of coccidia in the feces of normal goats does not indicate a disease situation. When an outbreak begins, only good sanitation and isolation of sick animals will prevent its spread through the herd. Coccidia eggs are resistant to disinfectants and may survive more than a year in the environment. They will stay alive in a pasture as long as they are in a moist, dark environment but will die when temperatures drop below freezing. Goats that survive through a disease outbreak are usually immune to future problems.
Important facts to remember about coccidia are the following:
Coccidia are very host specific. Therefore the species of coccidia that infect goats infect goats only. Coccidia found in birds, cattle, dogs or even sheep will NOT infect goats.
Virtually every goat has some level of infection, but illness occurs only in some animals. Fecal samples from virtually any goat of any age, sex, breed, dry or lactating, etc. will contain coccidia.
THE DISEASE IS ALMOST ALWAYS GOING TO OCCUR IN YOUNG ANIMALS. KIDS LESS THAN 5 MONTHS OF AGE ARE MORE SUSCEPTIBLE. Kids will become infected early on from the environment. Adults will have immunity to the parasite that is pretty effective in preventing disease, but not infection.
The primary sign of coccidiosis is diarrhea. Look for disease in stressed animals. Happy, well nourished kids left with the doe may show no diarrhea until they are, weaned. THE STRESS OF WEANING MAY DEPRESS IMMUNITY ENOUGH FOR THE COCCIDIA TO GET THE UPPER HAND AND CAUSE DISEASE.
Control of coccidiosis include removing manure, not feeding off the ground or letting goats jump into feeders (a real challenge). Coccidiostats (preventatives) include amprolium (Corid®), decoquinate (Decox®) and lasalocid (Bovatec®). These products may be used in the feed or water to prevent the development of the disease.
Drugs used to treat clinical cases of coccidiosis include sulfa drugs and amprolium. The doses to use can be found in the "Goat Health Handbook" authored by Dr. Thomas R. Thedford and published by Winrock International. This very handy book can be purchased through NCMGA. At NCSU, we drench severe cases, for 5 days, at the rate of 22.7 mg Amprolium per pound body weight, or .25 ml / lb body weight of 9.6% Corid (Amprolium) solution.
Factors to take into consideration about the use of drugs
Read label carefully - labeling directions change frequently
Use the proper dose for the size and species of animal to be treated.
Calculate preslaughter drug withdrawal time accurately. - withdrawal and discard times begin with the last drug administration
Use the correct route of administration - giving drugs incorrestly can lead to drug ineffectiveness, adverse reactions, illegal residues, and possible animal deaths.
DO NOT DOUBLE DOSE - use of the same drug in the feed and by injection can cause illegal residues.
Select needle size and injection site carefully, if injections are necessary - misuse can lead to tissue dmage, reduced effectiveness, and/or illegal residues.
Keep accurate records of drugs used and animals dosed - poor records can be costly if drug residue violations occur.
If possible, seek the advice of your veterinarian.
GENERAL DEWORMING PROGRAM
At NCSU, animals are wormed according to fecal egg count. However, it is a good idea to deworm prior to or very shortly after kidding to prevent periparturient rise in parasite egg production. If deworming takes place before kidding, make sure that the dewormer is safe for pregnant animals.
For dewormer to be effective, it is important to correctly estimate the weight of the animals. In a group of animals, calculate dose for the heaviest animal. Underdosing is a problem that can lead to parasite drug resistance. In addition, for goats, it is recommended to use 1.5 times the prescribed dose calculated on a body weight basis. Dewormers should be rotated annually.
Dose with Corid at 8 wks of age. Preventive treatment around weaning has proved effective in our situation.
This article was the result of numerous conversations held with Dr. Kevin Anderson from the College of Veterinary Medicine, NCSU, Raleigh, the copilation of articles and short notes written by Dr. Anne Zajac from the Virginia Polytechnic Institute and State university, Blacksburg, Drs. Kevin Anderson, Daniel Amaya, Jeff Musser, Sandy Grant, Dan Moncol and Michael Levy from the College of Veterinary Medicine, NCSU, Raleigh, and Dr. Thomas Thedford, who wrote the Goat Health Handbook, and finally the copilation of notes taken during field days and 'goat meetings'.