Ectoparasites (Ornithonyssus sylviarum) and sleep disruption in White Leghorn laying hens

Northern fowl mites (Ornithonyssus sylviarum) are common parasites in caged laying hens in the US. Mites feed on blood and are pathogen vectors, with infestation resulting in reduced egg production and feed conversion ratio. Mite infestation causes skin irritation, possibly disrupting the hens’ resting behavior. Unimpeded nocturnal resting is important for health and welfare, for example for energy conservation, tissue restoration, tissue growth and memory formation. Our aim was to study the impact of northern fowl mite infestation on nighttime behavior in laying hens. Sixteen beak-trimmed White Leghorn hens were individually housed in cages. They were experimentally infested with circa 35 mites at 25 weeks (wk) of age and observed for the behaviors “active”, “preening”, and the sleep-related states “dozing” and “sleeping”. Focal continuous observations were based on infrared video recordings from 22:00h until 06:00h (dark period, lights off) for two consecutive nights at wk 0 and wk 3 postinfestation. Data were analyzed with linear mixed models, testing for the fixed effects time of night and time from infestation on frequency and duration of behaviors. Preliminary results from wk 0, when none of the hens had mites, and wk 3 (mean of 676 mites/hen) show that dozing was the most common behavior (85% of time; 13 bouts per night), followed by sleeping (6.3%; 7 bouts), preening (2.4%; 10 bouts) and active (0.9%; 8 bouts). Mite infestation increased preening from 7.6 (wk 0) to 10.4 bouts (wk 3, P<0.01) and dozing from 10.7 to 13.6 bouts (P<0.01). Amount of time spent preening increased with increased mite load (P<0.01) but the change was non-significant for dozing. Mite infestation increased the frequency and duration of preening in hens, and shortened their dozing bouts (increased frequency with unchanged duration), suggesting welfare impairment due to irritation.