Failure of brewer's yeast as a repellent to fleas on dogs

Active and inactive brewer's yeast, when given as a dietary supplement to dogs at the rate of 14 g/day, failed to repel or kill fleas. Twenty dogs in each of 3 groups were inoculated weekly for 7 weeks with 100 unfed cat fleas (Ctenocephalides felis). One group served as a control while one group received inactive and the other active yeast during the last 5 weeks of the trial. There were no significant differences in flea counts among the 3 groups during the first 4 weeks of yeast supplemental feedings. Total flea counts during the 5th week of yeast supplementation did not differ significantly from the counts on control dogs, although there was a significant difference between counts from dogs receiving active and those receiving inactive yeast.