Potential Updates on Storage of Equine Fecal Samples for Parasite Analysis

Fecal samples from livestock sometimes need to be stored for later parasite analysis. Refrigeration for up to 1 week is the best way to preserve helminth egg counts in fecal samples from horses, according to a study recently published in Veterinary Pathology.

Fecal egg counts in individual animals allow anthelmintic treatment to be tailored to each animal; blanket administration of anthelmintics to livestock herds has caused drug resistance. The best time to perform a fecal egg count is soon after defecation, before egg hatching affects the count. Because this is not always practical, however, samples are often preserved by refrigeration or by longer-term storage in fixatives such as ethanol and formalin.

Researchers from the University of Sheffield, United Kingdom, sampled 10 “defecation events” from each of 3 horses that were initially shedding more than 200 helminth eggs per gram of feces. Storage methods tested were 40% and 70% ethanol, 5% and 10% formalin, and refrigeration. Egg counts were assessed with a modified McMaster technique.

Fecal samples were stored in each fixative solution for 4 weeks. Egg counts were assessed at baseline (fresh samples) and after 2 and 4 weeks of storage. The number of eggs recovered was significantly lower at 2 weeks than at baseline for all fixatives. Egg counts did not significantly decrease from 2 to 4 weeks. The decline in egg count was uniform across all samples in all 4 fixative solutions tested.

Egg counts were performed daily in refrigerated fecal samples. Refrigeration for 7 days did not significantly affect egg counts. However, egg counts declined by an average of 44% after 14 days of refrigeration. The decline became noticeable on day 8 and significant (P < .05) on day 10.

The authors conclude that refrigeration for no longer than a week will preserve helminth egg counts in horse feces, although analysis of fresh samples is best. Because the egg count decline in fixative solutions is uniform, egg counts from fixative-preserved samples could potentially be used to estimate the degree of egg shedding in infected horses.

The study was funded by the Righ scholarship, the Natural Environmental Research Council, and the Leverhulme Trust.

Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University in 1994. After an internship at Auburn University College of Veterinary Medicine, she returned to North Carolina, where she has been in companion animal general practice for over 20 years. Dr. Walden is also a board-certified Editor in the Life Sciences and owner of Walden Medical Writing.