Author
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Gasbarre, Louis |
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Submitted to: North American Veterinary Conference Proceedings
Publication Type: Proceedings Publication Acceptance Date: 9/10/1997 Publication Date: N/A Citation: N/A Interpretive Summary: Gastrointestinal nematodes cost the American cattle industry in excess of $2 billion per year. Because the different species of parasites vary greatly in their pathogenicity, control of these infections requires easy and accurate means to identify the parasite species in both individuals and din the entire herd. The current method of choice involves collection of feces from the cattle, followed by culture of the parasite eggs to grow larval worms. These worms are then identified to determine the parasite species present. We have found that this technique cannot be used to determine the numbers of each parasite species present unless the efficiency of the culture technique is defined for each species. We found that under a given set of conditions certain parasites will develop at higher rates than will other species. A second means to determine parasite especies involves differentiation of the parasite eggs in the feces. Simpl visual identification is inaccurate. Recent reports have used computer measurements to aid the differentiation. These techniques can differentiate the parasite eggs but they are very time consuming, and require expensive equipment. Recent attempts to differentiate eggs based on techniques of modern molecular biology offer promise, but still require extensive testing and adaptation to clinical laboratory conditions before they will be of everyday use. This information is of direct use to veterinarians and animal health consultants in the formulation and evaluation of parasite control programs. Technical Abstract: Proper control of gastrointestinal nematode parsites of cattle is dependant upon the correct measurement of parasite infection levels in the herd. Current means to measure parasite levels include the use of tracer calves, pasture larval counts, the measurement of serum pepsinogen levels, and the enumeration of parasite eggs in the feces. Because of both complexity and cost of the other techniques, only fecal egg determinations are routinely used. We have found that the repeatability of fecal EPG determinations is approximately 0.6, and that the accuracy of the measurement is moderately precise. This means that the most precise measure of a true EPG value would involve repeated daily sampling for 2-3 days, but that extended sampling beyond this would be of little value. Because the parasites are not normally distributed, when sampling in a herd, at least 15-20 animals should be sampled. Although such sampling gives a fair estimate of the true herd EPG value, this value is a very poor indicator of the number of Ostertagia in the host. Fecal egg counts are a measure of more fecund but less pathogenic trichostrongyle species such as Cooperia. As such fecal EPG values can be used to assess overall parasite transmission in the herd if the sample taken is large enough, and includes a representative sample of different age classes. But fecal EPG s are very poor indicators of parasite burdens in individual animals, and should not be used to predict parasite induced production losses. |
