Effects of the northern fowl mite on White Leghorn chickens.

Abstract

Experiments were conducted with Ornithonyssus sylviarum (Canestrini & Fanzago) on White Leghorn hens on a commercial poultry ranch in California. Weekly examination of all liens during test periods of 5 to 6 months showed that mite ratings of 0, 1–25, 50–1000, and 25,000–100,000 were reliable under experimental conditions except that laboratory counts from samples of mites on hens in the last 2 ratings revealed that numerical ratings were about ⅓ higher than the number counted. Egg production means were not significantly different among older hens, pullets, or on any one of 8 different family lines rated negatively, moderately, or heavily mite-infested. Low egg production was evident among hens which received a low protein ration, but mite-infested hens on the ration produced more eggs than their noninfested counterparts. Whole blood and serum analyses from heavily infested and noninfested hens in 2 experiments showed that mean protein values were not statistically different. Packed cell volume of heavily infested hens was not lower than that of clean hens, suggesting that anemia is not a symptom of heavy mite infestation. In general, skin scabs in the vent region of hens were more numerous as mite counts neared 100,000, and molted hens showed an increase in their number of mites which was contrary to the general opinion that mite infestations declined during and after a molting period. The application of 0.5% carbaryl spray to all hens in 1 experiment resulted in poor and good mite control on heavily and moderately infested hens, respectively.