Old horses have higher worm egg counts

Old horses have significantly higher faecal worm egg counts, and show a different inflammatory and immunological responses to anthelmintic treatment than do middle aged horses, according to recently published research.

The study, conducted by Amanda A. Adams and colleagues compared the faecal worm egg count (FEC) response to treatment of middle-aged adult horses (5–15 years old) and older horses (20–33 years). They also measured the inflammatory response of the horses when dewormed with either moxidectin or pyrantel.

Horses in each age group were treated with either moxidectin or pyrantel, or were left untreated. Before treatment and 14 days later, the researchers collected samples for faecal worm egg counts and for detection of Strongylus vulgaris by polymerase chain reaction (DNA testing). They also collected blood samples at regular intervals after treatment to assess the inflammatory response to treatment.

They found that old horses had significantly higher FECs than middle-aged adults. They suggest that the higher FECs found in the old horse group may have practical implications for parasite management routines on farms with representation of this age group.

FECs declined significantly after anthelmintic treatment in both age groups.

Inflammatory markers differed between age groups and with anthelmintic treatment. Old horses seemed to produce more marked responses to anthelmintic treatment.

Moxidectin treatment appeared to be associated with less inflammatory reaction after treatment when compared with pyrantel pamoate. The researchers suggest that further studies are needed to evaluate the clinical significance of these findings.

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