Factors affecting northern fowl mite populations on chickens: effect of age of pullet at time of infestation and effect of caponizing roosters.

Pullets were infested with northern fowl mites (NFM), Ornithonyssus sylviarum (Canestrini and Fanzago), at 12, 16, 20, 24, and 28 weeks of age to determine the best age for infesting hens to obtain uniform heavy NFM populations and to determine if NFM infestations affected initial egg production. Populations of NFM were significantly heavier, developed faster, and declined faster when pullets were infested at 24 or 28 weeks of age than when infested at younger ages. The time of mean initial egg laying was not affected by infestation with NFM at any of the different ages. Cockerels caponized at 4 weeks of age carried significantly fewer NFM than did control males. Feather development appeared to play a significant role in the population levels of NFM on both the hens infested at the earlier ages and in the capons.