J Am Vet Med Assoc. 1983; 183(2): 212-4.
Failure of brewer's yeast as a repellent to fleas on
dogs.
Baker NF, Farver TB.
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.