I have heard that about garlic too. The study was published in the Archives of Animal Nutrition by two researchers at the Institute of Poultry Diseases in Berlin:
http://www.tandfonline.com/loi/gaan20
"Efficacy of a herbal product against
Histomonas meleagridis after
experimental infection of turkey poults"-
Prof. Hafez Mohamed Hafez a
& Rüdiger Hauck aa
Institute of Poultry Diseases, Free University Berlin , Germany
Published online: 25 Jan 2007.
I have heard alliums are not to be given to chickens but then others say to give garlic for worm prevention. Very confusing to me.
I think I will try the red pepper flakes