I give my dogs Brewers Yeast Tablets every day. Three in the morning and three at night for a
70 - 100 lb dog and two in the morning and two at night for a 40 to 70 lb dog. They work really well for repelling any fleas. It takes about a week or so for it to distribute to the skin. You must give these to them daily or it will not work. I get them from Walmart in the Vitamin section, about $3 for a 250 tablet bottle named Spring Valley Natural Brewer's Yeast. It helps to keep the mosquitoes off of them too.