Variations in different fecal egg count methods in horses highlighted

Researchers put forward correction factors to help standardize results from various fecal egg count techniques in horses.

Researchers have put forward what they term correction factors to help standardize the results from different fecal egg counting methods in horses.

The study team, writing in the journal Pathogens, noted that the American Association of Equine Practitioners (AAEP) strongly advocates for evidence-based intestinal strongyle control in horses.

It recommends targeted treatment of all heavy egg shedders (with more than 500 eggs per gram of feces), while the low shedders (0–200 eggs per gram) are left untreated.

“As 50–75% of adult horses in a herd are low shedders, preventing them from unnecessary anthelmintic exposure is critical for tackling resistance,” Manigandan Lejeune and his fellow researchers said.

There are various fecal egg count techniques, with many modifications and variations in use. However, none is identified as a gold standard.

The Cornell University study team in New York state tested the diagnostic performance of three egg counting techniques — the modified Wisconsin, modified McMaster, and Mini-FLOTAC methods.

Variants of these methods centered on the choice of floatation solutions — either sodium chloride, sodium nitrate, sugar or zinc sulfate.

The study team hypothesized that the diagnostic performance of the three techniques with four variants would differ. This proved to be the case.

They conducted a comparison study using polystyrene beads as a proxy for intestinal strongyle eggs. The beads were used to overcome the difficulty of procuring extracted/purified eggs for such a large-scale study.

Results differed considerably.

Their work identified five tests that performed with better accuracy than the others — the Mini-FLOTAC method using either salt, sodium nitrate, sugar on zinc sulfate as the flotation mediums, and the modified Wisconsin method using a sodium nitrate solution.

The Mini-FLOTAC method seemed less influenced by the choice of floatation solution and had better repeatability parameters for bead standard recovery, they said.

Despite the suitability, the raw egg count estimate differed in each case, and a correction factor determined for each test based on regression analysis was applied to standardize methodologies. This pulled the results from the various methods closer into line.

The validity of the correction factor was analyzed for the five best-performing test variants to accurately quantify intestinal strongyle eggs from 40 different horses.

Agreement of fecal egg count categorization results (low 0–200; medium 201–500; and heavy 500+) between the five selected methods (x-axis) before and after application of correct factors. Forty fecal samples are indicated in the y-axis.
Agreement of fecal egg count categorization results (low 0–200; medium 201–500; and heavy 500+) between the five selected methods (x-axis) before and after the application of correct factors. Forty fecal samples are indicated in the y-axis.

Equalizing the fecal egg counts based on AAEP egg-shedding categories (low, moderate, and heavy) allows for a standardization of fecal egg count methods, they said.

“Selecting a suitable test with the application of the correction factor is the key to determining accurate fecal egg counts,” they said.

This, they said, will facilitate meaningful approaches for targeted control of intestinal strongyle infections and effective management of drug resistance.

“Adjusted fecal egg counts should form the basis for controlling and management of equine strongylosis.”

In conclusion, they said their study identified fecal egg count methods with the highest diagnostic performance.

“The limitations in standardizing routine fecal egg count tests are highlighted, and the importance of equalization of fecal egg count results is emphasized for promoting uniformity in the implementation of parasite control guidelines.”

The study team comprised Lejeune, Sabine Mann, Holly White, Danielle Maguire, Jaime Hazard, Rebecca Young, Charles Stone, Doug Antczak and Dwight Bowman, all with Cornell University.

Lejeune, M.; Mann, S.; White, H.; Maguire, D.; Hazard, J.; Young, R.; Stone, C.; Antczak, D.; Bowman, D. Evaluation of Fecal Egg Count Tests for Effective Control of Equine Intestinal Strongyles. Pathogens 2023, 12, 1283.

The study, published under a Creative Commons License, can be read here.

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