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Parasites Don’t Make Your Horse Run SlowerBy Dr. Peter Huntington · October 31, 2011
Most horses are routinely dewormed at regular intervals without regard for their parasite burden. Whilst horses in paddocks may need regular deworming to reduce the number of eggs deposited in the paddock so that the infective larval population can be controlled, horses kept in stables don’t have to be dewormed for pasture hygiene reasons. Stabled horses don’t have the same exposure to larval stages for reinfestation, so the major reason for deworming is to remove mature parasites and susceptible larvae that might be damaging to a horse’s health and performance.
A Danish study looked at the association between parasite burden as judged by faecal egg counts (FEC) and performance in 213 Standardbred trotters. The FEC is an indicator of the adult parasite burden in the horse, and higher numbers are associated with more adult parasites. Horses came from a number of stables and had varied deworming histories, but all had regular deworming protocols in place. The FEC ranged from 0 to 3,000 with the median being 300, and there was no association between a low FEC and better performance. In fact, horses with the best performance had significantly higher FEC than those that did not place in races.
So, whilst not advocating that higher parasite burdens are performance-enhancing, it does seem that they are not a limiting factor either. As the frequency of deworming is associated with faster development of anthelmintic resistance and involves a cost to the owner, it seems that stabled racehorses could be dewormed less frequently. Targeted deworming of individual horses showing signs of parasite infestation should be considered rather than a blanket program where every horse is treated.
