Preliminary observations on northern fowl mite infestations on estrogenized roosters and in relation to initial egg production in hens.

Treatment of normal male Leghorn chickens with doses of estradiol ranging from .1 to 1.0 mg per week caused only a slight increase in resistance to infestation with northern fowl mites. The resistance phenomenon did not increase linearly with estradiol dose. Pullets were initially resistant to mite infestation; however, susceptibility was noted to increase markedly near the time of initial egg-production. These data indicate that sex hormones may be related to mite resistance in chickens, but that estrogen alone is probably not responsible for the difference in mite susceptibility between male and female birds.