Fleas are a common problem with nearly any animal that spends time outdoors, and horses are no exception. To keep the fleas away from the horses, you must use a routine that safely gets rid of the fleas without harming your horses. After you initially treat the horses, follow a preventive routine that stops the fleas from attacking the horses in the future.
Fill a bucket with about 4.5 litres (1 gallon) of water and 60 ml (1/4 cup) of dish soap. Mix the ingredients with your hand to dissolve the soap.
Brush over the horse with a large flea comb. This will take a while but ensures a thorough cleaning of the horse. Dip the brush into the bucket of soapy water as needed when you collect fleas. The soap will trap and smother the fleas instantly.
Comb the mane as well as fleas can often linger in these areas.
Fill a spray bottle with equal parts water and white vinegar. Mist this over your horses, staying away from eyes, nose, mouth and genitalia. The vinegar emits a bitter scent and taste that repels fleas. Reapply the spray every two days or so.
Add about 6 ml (1 tsp) of white vinegar to your horse's water trough per gallon of water used. This will typically be too little for the horses to notice, but will be effective in getting vinegar into the horses bloodstream, thereby repelling fleas.
Continue this routine every two days until all signs of the fleas are gone; after this, treat your horses weekly to prevent fleas from returning.