Diagnostic tests used in small ruminants:
- Fecal flotation: Fecal flotation gives a broad overview of the parasites present (nematodes, cestodes, protozoa). Results are assigned semi-quantitative results (Rare, few, moderate, high, very high). It should not be used to assess treatment efficacy for strongyles.
- McMaster Egg Count: The McMaster method should be used to quantitate strongyle nematode egg burdens. It has poor repeatability for quantification of Eimeria. If McMaster egg counts conducted before and 14 days after deworming show less than a 90% reduction in egg counts, the strongyles are considered drug resistant. On a herd level, it is recommended to test at least 10 to 15 animals to assess drug resistance.
- Fecal/Baermann sedimentation: Sedimentation methods are used to detect trematode eggs and lungworm larvae.
Considerations for interpretation of results:
At a population level, it is expected that grazing ruminants have some level of parasitism. Accordingly, nematodes and coccidia will almost always be detected, especially in fecal floats. Therefore, diagnostic reports of parasitism should be critically interpreted before implementing herd-level recommendations. Since parasites are normally present in herbivores, it is critical to rule out other differential diagnoses for the clinical sign of concern. In general, fecal flotation results of “rare” or “few” parasites are not considered to be clinically significant.
At a population level, under normal conditions, parasites are over dispersed. That means that a few individual animals have many parasites while most animals in the herd have a moderate to low level of parasites. In general, the fecal exam from a single animal or few animals from a large population are unlikely to represent the status of the entire group. Animals that have concurrent disease processes (bacterial, viral, nutritional, etc) are likely to have increased numbers of parasites as a result of a compromised immune system.
Interpretation of specific parasitology test findings:
Nematodes: Strongyles are the most important group of nematodes infecting small ruminants. There are many species of strongyles; the most pathogenic is Haemonchus. Haemonchus causes anemia; it does not typically cause diarrhea. However, other strongyle species have the potential to cause diarrhea. Fecal floats and McMaster egg counts do not discriminate Haemonchus from other strongyle species. When considering Haemonchus/strongyles as a cause of disease, McMaster egg counts should be conducted. There is not a standard number of eggs per grams considered to be significant. Counts of >300 eggs per gram may be associated with clinical disease, counts of greater than 1000 eggs per gram are considered to be clinically significant. On a herd level, it is common for many animals to have 0-500 eggs per gram while a few individuals have several thousand eggs per gram. Small ruminants also become infected with other nematodes such as Trichuris, Strongyloides, and lungworms. These nematodes are less commonly a cause of disease in ruminants in Iowa. Fecal flotation results of “high” or “very high” levels of these parasites may indicate clinical significance.
Cestodes: Ruminants become infected with Moniezia spp. tapeworms. In general, these parasites do not typically cause clinical signs but they may result in decreased feed efficiency. Fecal flotation results of “high” or “very high” levels of these parasites may indicate significance.
Protozoa: The most common protozoan infecting small ruminants is Eimeria, commonly referred to as coccidia. Fecal flotation results of “moderate”, “high”, or “very high” may indicate that the finding is clinically significant. Counting Eimeria organisms (McMaster) for assessing treatment efficiency has poor repeatability.