Introduction/Causative Agents:Coccidiosis is a world wide contagious disease of sheep and goats, especially young lambs or kids. The disease is caused by one or more of approximately 12 different species of protozoa called Eimeria. These organisms parasitize and destroy cells lining the intestinal tract of the animal. Because each of the 12 or so coccidia species is completely independent from the others, with no cross immunity, an animal that is living with one type of coccidia may develop diarrhea when exposed to a different type. Good nutrition (including vitamin E-selenium supplementation in selenium deficient areas) also helps the animal defend itself against coccidiosis.
Whether or not an animal gets sick with coccidiosis depends on several factors. One is the number of oocysts (eggs) swallowed at one time. Small exposures, frequently repeated, lead to immunity; while large exposures destroy all the intestinal cells at one time and may kill the lamb or kid. The age of the animal is also important, partly because the older animal has usually had time to develop some immunity, while the younger animal can be very vulnerable to disease. Immunity to coccidiosis in healthy adult animals is rarely complete, yet most of the intestinal cells in the adult are safe from invading coccidia. This means that a healthy looking adult sheep or goat can continue to pass oocysts in the fecal pellets.
Disease Transmission and Life Cycle:An infected animal sheds thousands of microscopic coccidial oocysts (eggs) in its feces every day. When first passed, the oocysts are harmless to another animal. However, under favorable conditions of warmth and moisture, each oocyst matures (sporulates) in 1-3 days to form infective sporozoites. If a young lamb or kid swallows the sporulated oocyst, the sporozoites are released and rapidly penetrate the intestinal cells. From here on the life cycle gets very complicated. The coccidia pass through several periods of multiplication during which large schizonts are formed. The intestinal cells of the animal are destroyed and thousands of merozoites break out and invade other intestinal cells. Eventually, sexual stages are reached and new oocysts are produced. The entire life cycle of the protozoa, from oocyst to new oocyst, takes 2-3 weeks.
Clinical Signs:If a young lamb or kid is suddenly exposed to many sporulated oocysts, it may become severely ill 1-2 weeks later. It will be off feed, listless, and weak. It may show abdominal pain by crying or getting up again as soon as it lies down. At first, the young animal might have a fever, but later the body temperature is normal or even below normal. Diarrhea begins pasty, then becomes watery, and the lamb or kid may dehydrate rapidly. In contrast to calves, lambs and kids only rarely have bloody diarrhea. Because the lactic acid produced by the digestion of milk helps to inhibit coccidia in the nursing young, signs often appear 2-3 weeks after the animals are weaned. Many of these signs are brought on by the stress of weaning or overcrowding.
Young lambs or kids may be killed quickly by a severe attack of coccidiosis. The stronger or less heavily infected animals will develop a chronic disease characterized by intermittent diarrhea and poor growth. Tails and hocks are often dirty. Because the intestines have been severely damaged, the animal with chronic coccidiosis cannot digest its feed properly. As a consequence, such an animal will be a pot-bellied, poor-doer for months afterwards. Frequently, a stunted lamb or kid will be too small to breed its first winter.
Even though coccidiosis is typically a disease of the young, growing lamb or kid, many adults are mildly infected and continuously shed oocysts which serve to infect the young lambs and kids. Occasionally, an adult sheep or goat shows temporary diarrhea when stressed or exposed to a new species of coccidia. This is especially common after the ewe or doe has been boarded on another farm for breeding.
Diagnosis:Diagnosis of coccidiosis can be based on clinical signs and microscopic fecal exams. Coccidiosis is so common that it should be suspected whenever lambs or kids older than about 2 weeks of age are scouring. Sudden dietary changes or excessive food consumption can also cause diarrhea and make the animal more susceptible to coccidiosis. Diarrhea that begins with the consumption of too much milk, grain, or lush grass may drag on for days because of coccidiosis. Older lambs/kids and adults with diarrhea may have worms rather than coccidiosis, or they may have both problems together.
Coccidia oocysts can be identified if fecal material is mixed with a concentrated sugar solution. The oocysts float to the top along with larger worm eggs. They are collected and examined with a microscope (see page D228). Oocysts may be shed in the feces as early as 10 days after a animal is infected, but often the first attack of diarrhea occurs before oocysts are available to be identified. In these cases, the trained technician can do a direct fecal smear to look for smaller merozoites that do not float in the sugar solution.
If a lamb or a kid dies of coccidiosis, necropsy examination will quickly give the diagnosis. The small intestine will have many irregular raised white areas, often about 1/8 to 1/4 inch in diameter. A smear taken from these white spots will show many coccidial forms if examined using a microscope.
Treatment:A variety of drugs may be given orally to treat the lamb or kid sick with coccidiosis. These include medications such as sulfamethazine, sulfadimethoxine, amprolium, and lasalocid. Usually, treatment is continued for about 5 days. Label and veterinary instructions should be followed because of the associated dangers if overdosed. If the diagnosis is not certain, and the young animal may have bacterial enteritis or pneumonia rather than coccidiosis, sulfamethazine or sulfadimethoxine is usually given instead of the others.
All of these drugs are coccidiostats, which means that they slow down rather than kill the coccidia. Thus if a lamb or kid is very heavily infected when treatment is begun, the medication may not help that much. These drugs will, however, greatly reduce contamination of the environment and thereby, give other young animals time to develop immunity.
Medicating older animals or adults will temporarily reduce the passage of oocysts, but will not improve growth rates. Within 2 or 3 weeks after medication is stopped, coccidia levels will return to pretreatment values. Thus, except for protection of younger lambs and kids, it is not justifiable to treat older, apparently healthy animals that do not have diarrhea. It is far better to separate the young animals from these older carriers. It is neither possible nor desirable to completely eradicate coccidia from the adult sheep and goats.
Medication of apparently healthy lambs and kids is necessary on large farms with previous problems with coccidiosis. The aim is to prevent damage to the intestines rather than waiting for diarrhea to occur. For instance, it may help to treat the young animals with coccidiostats on a daily basis for a week or more before stressing them by weaning or by moving them onto pasture. In some herds/flocks, a drug such as amprolium may have to be given daily beginning at 2 weeks of age and continue until the young animals are several months old. Amprolium levels of 25-50 mg/kg daily should be used. This is approximately 10-20 mg per pound and is 2.5-5 times the treatment level recommended for calves. It can be given to each lamb or kid individually or can be mixed with the food or water. For example, if there are 50 pounds of small lambs or kids in a pen, 500 mg of amprolium is mixed with the water, milk or feed that they will consume in one day. The larger animals, by eating more, get more of the drug than do the smaller ones. Rumensin (monensin) at 15-30 grams per ton of feed in the starter grain has been found to eliminate the coccidiosis problems on some farms. This drug is very toxic to horses, so the medicated feed should not be left where a horse can eat it. Another potentially useful coccidiostat is lasalocid. This drug has protected lambs when used at 0.5-1.0 mg/kg/day. The poultry industry has found that the coccidia often become resistant to a drug after 1 or 2 years. Sheep and goat owners may also need to change drugs if the one in use ceases to be effective in controlling coccidiosis. Other coccidiostats may be mixed with the feed, but some of them have not yet been adequately tested on sheep and goats.
No matter what medication is chosen, it is important to consult a local veterinarian before attempting to use any of these products. Many of the above products are used in extra label amounts and are not approved for use in sheep and goats in the United States outside of the proper veterinarian/client/patient/relationship (VCPR).
Prevention: Prevention of coccidiosis is very important in larger flocks and herds if young lambs and kids are to thrive. Once diarrhea has developed, most of the damage to the intestine that leads to stunted growth has already occurred. Sick, young animals are treated to save their lives and to limit contamination of the pens, but at this stage, the owner has already lost control of this contagious disease.
Several key facts are important to consider when developing a prevention program. The first is that adult animals are the original source of infection for young lambs and kids. The adults continually shed oocytes that contaminate the environment and younger animals. Because of this, all old bedding and feces should be removed from the lambing and kidding pens before the new lambs and kids are born. Sporulated oocysts are commonly present on the skin of the udder, and the young, suckling animal may become infected at the same time it takes its first drink of colostrum. To prevent this from happening, the female’s udder should be washed and dried before the young nurse, or the lamb or kid should be removed from its dam at once and bottle-fed the colostrum. If very few ewes and does are present on a farm and the pens are dry and spacious, coccidiosis is not apt to be a problem. The young may be safely left with their mothers. In larger flocks or herds, it is best to raise offspring completely separate from the adults until they are ready to breed.
Fecal contamination of feed and water must be prevented. This means that feeders and waterers should be outside the pen whenever possible and arranged so that fecal pellets can not fall into them. Grain should be put in creep feeders rather than in open troughs where lambs and kids love to play and even sleep. Hay racks also should be covered to keep the young animals out.
Because oocysts have to sporulate to become infective, exposure can be reduced by cleaning the pens daily. Slotted floors are helpful in this process. Because moisture is necessary for sporulation, concentrate on keeping the pens very dry and fixing leaking waterers at once. Small, grassy "exercise lots’’ are also very dangerous and should be used with caution. It is very important to avoid overcrowding; spreading the lambs or kids out decreases the number of oocysts on any given square inch of pen floor or pasture. If many lambs or kids are present on the same farm, they should be grouped by age. Putting a 2 week old kid into a pen with kids 2 months old, where coccidial numbers and immunity have been building up for some time, is to invite disaster for the newcomer. Oocysts are killed by very cold temperatures (far below zero) or by hot, dry conditions above 104° F. This means that at the end of the kidding/lambing season, pens and feeders could be moved out into the hot sunshine for natural sterilization. Ordinary disinfectants do not destroy oocysts and should not be relied on for control of coccidia.