Garlic to Repel Biting Flies on Horses

I heard that horse should be fed garlic daily to repel biting flies. How much would I give my Belgian mare? Her weight is 1700 pounds.

Garlic may be fed at six to eight crushed cloves daily in feed. Caution should be exercised if your mare is lactating as the taste of garlic may flavour the milk and upset the digestive system of her foal.