Performance horses are often treated routinely with anthelmintics on the assumption that low grade infections may reduce their athletic ability. However, these intensive anthelmintic treatment regimes may not be justified according to research conducted in Denmark.

A study, under the direction of Dr Martin K Nielson of the University of Copenhagen, correlated the racing performance of Danish Standardbred trotters with faecal worm egg counts (FWEC). All horses in the study had been treated regularly for worms, although none of them had received anthelmintics within the 12 weeks prior to sampling.


A large proportion of the Danish racing Standardbred population were included in the study. Samples were collected from 213 horses out of the total of 590 Standardbred trotters registered for racing.

The research team assessed the effect of strongyle egg counts on finishing position and the value of the race winnings.

They found an association between finishing position in races and FWEC, which was statistically significant. However, contrary to what might be expected, horses finishing in position 1-3 actually had higher FWEC than those finishing unplaced.

The data also suggested higher winnings were achieved by horses with higher FWEC, although this association was not statistically significant.

The researchers conclude that, in this study of professionally-trained Danish Standardbred trotters, racing performance was not negatively affected by higher strongyle faecal egg counts.

They suggest that further studies are needed to explain the effect of strongyle worm burdens on performance horses and to identify suitable anthelmintic treatment regimes for the high performance athlete.

For more details see:

Strongyle egg counts in Standardbred trotters: Are they associated with race performance?
P Fog, H Vigre, MK Nielsen.
Equine Vet J (2011) 43, (Suppl 39) 89 - 92