THE RELIABILITY OF A SINGLE FECAL EGG PER GRAM DETERMINATION AS A MEASURE OF INDIVIDUAL AND HERD VALUES FOR TRICHOSTRONGYLE NEMATODES OF CATTLE

Authors: GASBARRE, LOUIS; LEIGHTON ELDIN A - C-BAR GROUP, GRT FALLS,VA; BRYANT DEAN - UNIV MD, QUEENSTOWN, MD

Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/1994
Publication Date: N/A
Citation: N/A

Interpretive Summary: The number of parasite eggs passed in the feces has been used extensively to assess parasite infection levels in cattle. The purpose of this study was to determine the precision and accuracy of the method used to determine the number of parasite eggs. The results indicate that when a minimum of 15 to 20 individual animals are sampled, the fecal egg count procedures accurately define the average egg output of the herd. In contrast, the procedures used provide only a rough estimate of the "true" number of eggs passed by a given individual animal. Repeated sampling of the individual enhances the accuracy of the estimate, but the increase in accuracy is most probably not worth the elevated cost associated with the multiple determinations. Although fecal egg count determinations provide only a rough estimate of the "true" egg count of individual cattle, the level of precision is high enough to allow the use of this method in genetic selection. These results are important because they provide practitioners and producers with the information necessary to determine the number of animals and the number of repetitions necessary to acquire accurate information on the number of parasite eggs passed by cattle. Knowledge of parasite egg levels is important in determining the necessity of drug treatments and for other management decisions aimed at controlling infection.

Technical Abstract: The level of trichostrongyle eggs per gram of feces (EPG) is important in the assessment of parasite burdens and parasite transmission in cattle herds. The goals of this study were to determine the precision of a single fecal egg count, to evaluate the necessity of repeated sampling to ascertain the EPG level of a given animal, and to infer the number of cattle that must be sampled to estimate the mean EPG value of a given herd. Angus calves born in 4 successive years were sampled for 3 consecutive days in May, July, and September. The largest variation in these fecal egg counts arose from differences among calves. Variation associated with sampling within calf was larger than that associated with the year of sampling or the day of sampling. Repeatability of EPG determinations was 0.4 to 0.6. At this level, the collection of 3 replicate samples reduced the variance associated with a single calf mean by 1/3. Additional replication further reduces the variance at a diminishing rate. To accurately estimate mean EPG for a herd, a randomly drawn sample should be similar in composition to the herd and include at least 1 animal from the high EPG group, (15 to 20% of the calves). To insure that, on average, 95% of the samples contain one or more high EPG animals, the sample must include 15 to 20 animals. These results indicate that a single fecal egg determination accurately assesses herd fecal EPG values when 15-20 individuals are sampled, but that a single fecal EPG determination is a relatively poor indicator of the "true" EPG value of a given individual.