Combining Nature & Science we have manufactured a powerful and effective fly spray using lemon citronelle, geranium oil, eucalyptus, tea tree, basil & neem oils along with other components that have a long lasting repellant effect on flies, a broad collection of insects and various other winged and multi legged friends.
 
When a horse exercises it's sweat dilutes the effectivness of other fly sprays, but not ours! Happy Equine's FLY OFF fly repellent  soaks itself into the horses hair ultimately providing a longer lasting effect.  Due to its natual ingredients of neem and tea tree oil its Gentle on the Skin but Firm on Flies.
 
Added benefit: You can also use it in the stable, woodwork and transport when out and about with your beasties as it doesn't effect the food chain.