by Joe Tritschler and Brad LeaMaster
Department of Animal Sciences Livestock Extension Team University of Hawai`i at Manoa
Sample collection
Fecal flotation The flotation method is based on the differential specific gravity of parasite eggs/oocysts and fecal debris. Eggs and oocysts float in saturated sugar or salt solutions, while most debris settles. This method will not detect fluke eggs or all nematode larvae (lung worm). These require more exact flotation solutions and procedures which can be learned from parasite laboratory manuals.
Procedure 2. Fill the tube completely with flotation fluid, then place a coverslip (or slide) across the top of the tube. The fluid should be brought up so that it is in contact with the coverslip. This transfers the eggs and oocysts to the coverslip. 3. The tube is left standing for 15 minutes or longer. Then the cover slip is removed by lifting it straight up and placing it on a slide. The slide is examined under the microscope (40X-100 magnification) for eggs and oocysts.
Parasites Nematode eggs are shed by a large number of nematodes, most of which cannot be easily distinguished from each other in a fecal examination. This whole group is commonly referred to as strongyle eggs and worming recommendations can be based on the quantity of strongyle eggs. Since fecal counts only estimate the parasite load, there is no clear cut level at which worming is indicated. As a general guide, a level of about 500 eggs per gram of feces would indicate that worming is needed for sheep or goats, or about 500 eggs per gram of feces for cattle. A more effective way of deciding when to treat would be to monitor fecals every 4-8 weeks and worm when there is a dramatic rise in egg counts. This would indicate increased pasture infectivity, so moving animals to another pasture would also be indicated. Nematodes are picked up by animals grazing pasture, and the parasite burden is related to the pasture infectivity. However, at the beginning of a dry season (or cold season at high altitude), larvae that are picked up from pasture can delay development. These inhibited larvae can be a serious problem, when they begin redeveloping, and there will be no high fecal egg counts to indicate this problem. Therefore, particularly if pasture infectivity has been high, young livestock should be wormed after the end of the wet season. Be sure to use an anthelmintic that is effective against inhibited larvae. The extent of this inhibition is unknown in Hawai`i. There are a couple of nematode eggs which can be distinguished from the large group of strongyles. These include Nematodirus sp., Trichuris sp., Strongyloides sp. and Ascarides. Nematodirus eggs are distinctly larger than strongyle eggs. Nematodirus can be a problem at the beginning of the grazing season in young lambs, kids and calves. Although Nematodims sp. is not very common in Hawai`i, where it exists even low levels of Nematodirus eggs per gram of feces would indicate that worming is needed. Strongyloides eggs are slightly smaller than strongyle eggs, and the larvae are distinctly visible within the egg. Trichuris eggs have distinct bipolar caps. While Strongyloides sp. and Trichuris sp. exist in most animals, they are only of concern in swine and possibly young livestock. Strongyloides sp. is only a common problem in suckling pigs. Ascarides are of concern in swine (Ascaris sp.) and horses (Parascaris sp.). Ascaris sp. and Trichuris sp. are a particular problem in pigs because they can survive for such long periods of time (years) in the environment. Young pigs (up to six months) are most susceptible. White liver spot from pork carcass data may also indicate Ascaris infection in the herd. Parascaris sp. in horses is only a problem in young foals. Trichuris sp. and Ascarides should be treated in young pigs and foals based on even low fecal egg counts. Nematode larvae, when present in the feces, are indicative of lungworm. There isn't any need to count lungworm larvae in the fecal examination. Generally, a serious respiratory problem suggests that lungworm may be present. The fecal examination simply tells one whether the respiratory problem is due to lungworm. It is possible to do fecals without finding the lungworms. However, lungworms will migrate from feces in a water solution (put mixture on screen or cheesecloth in a gravity funnel, collect small amount of liquid from bottom after several hours). To confirm a serious lungworm problem, worms will actually be coughed up 30-60 minutes after worming. Fluke eggs can be detected in feces, but a more accurate method is needed. However, since livers are condemned for flukes, a good method to initially check for flukes is to see if your livestock had any fluke condemned livers at slaughter. Flukes are a problem in the wet areas of Hawai`i, particularly standing water, such as swamp or marsh. The primary control for flukes is to fence livestock away from these wet areas. Tapeworm (Moniezia sp.) eggs may be seen in fecal examination but they are in no way indicative of the level of infection. Since tapeworm segments are visible in the feces, one can estimate the level of herd infection by looking at fecal pads or droppings. It is debatable whether tapeworms cause serious problems, so only very high levels of infection should be treated. Also, if one uses an anthelmintic that is less than 100% effective, it's control level may be sufficient for tapeworm control. This would most likely occur in heavily used pastures and paddocks. Coccidia oocysts are passed in the feces of most livestock. They are particularly a problem in young animals when raised in confinement or dense groups. Levels will generally decline as animals are spread out on pasture, and older animals develop immunity. Oocysts are only a moderate indicator of level of infection, because coccidia can multiply asexually in the intestine, which won't increase oocyst production. Oocysts appear very small, about a tenth the size of a Strongyle egg. To estimate the quantity of oocysts in a fecal examination, try to obtain an impression of the density per microscopic field. This can range from almost no oocysts to having a field full of oocysts. A medium to full field average would indicate that coccidia treatment should be given, particularly in young animals.
Summary Remember, there are different treatments for various parasites. In some cases change of environment may work by itself. When worming medications are used, be sure to use one that is effective against the parasite(s) for which you are treating. It often doesn't pay to treat for everything, when you only need to treat for a couple specific parasites.
Issued in furtherance of Cooperative Extension work, Acts of
May 8 and June 30, 1914, in cooperation with the U.S. Department of
Agriculture. Cooperative Extension Service, College of Tropical Agriculture
and Human Resources, University of Hawai`i at Manoa, Honolulu, Hawai`i
96822. An Equal Opportunity Employer providing programs and services to
citizens of Hawai`i without regard to race, color, national origin, or
sex.
Important |
||||||||||||||||
