Alternate grazing of horses and sheep as control for gastro-intestinal helminthiasis in horses.

This research studies the effect of alternating horse and sheep grazing on the control of gastrointestinal worm infections in horses. The study found that horses grazed after sheep showed significantly fewer nematode worms, but higher burdens of a specific type of worm, Trichostrongylus axei.

Research Method

• The study used two groups of Shetland ponies of similar number and age. One group continued to graze on the same pasture from February to September, while the other group alternated pastures – first a similar pasture from February to July, and then a pasture that sheep had grazed on from April to July.
• Both groups were treated with an anthelmintic medication, cambendazole, when the latter group was moved to the sheep pasture.
• Worm samples were taken from the pastures and the horses to analyze the populations of different species present. This comparison helped the researchers understand which worm species are favored or controlled under different grazing conditions.

Findings

• The group of ponies that grazed after the sheep showed markedly smaller burdens of nematode worms from the Cyathostominae and Strongylinae families. However, they had substantially higher burdens of a specific worm type, Trichostrongylus axei.
• The high number of Trichostrongylus axei worms in the rotated grazing group resulted in an increased level of serum pepsinogen, an enzyme marker indicating worm infection, within two weeks of moving to the sheep pasture. This level gradually decreased over time.
• Upon examination at the end-of-study autopsy, this group’s Trichostrongylus axei populations were almost entirely made up of immature (early third stage) worms.

Implications

• This study suggests that it is possible to control certain types of worm infections in horses through strategic grazing rotations. However, the results also indicate that this approach may increase the risk of infection from other types of worms.
• The relative benefits and drawbacks of such a method would therefore have to be carefully evaluated based on the specific worm types prevalent in a given region or farm.
• Using anthelmintics in combination with grazing rotation could potentially be a viable integrated strategy for worm control in horses, warranting further research.