Influence of the northern fowl mite (Acari: Macronyssidae) infestation level on cage-free laying hen welfare

As the most prevalent ectoparasite of North American laying hens, the northern fowl mite (Ornithonyssus sylviarum) negatively affects the productivity and welfare of millions of hens. Therefore, this study examined how mite infestation level affects welfare parameters of laying hens. Laying hens (housed in 5 pens within each of two rooms; 40 hens/pen) were each infested with 50 mites at 24 weeks (wk) of age. Welfare parameters (condition of the beak, footpads, and feathers; toe damage; keel bone fractures and deviations) and body weight (BW) were assessed at 20, 24 (prior to infestation), 26, and 30 wk. Mite score, skin inflammation, and skin lesions were evaluated at 26 and 30 wk. Hens were grouped into high (HIGH) and low (LOW) infestation level groups according to their 30 wk mite score. Differences between clusters were evaluated to compare welfare measures, mite scores, skin inflammation scores, skin lesion scores, BW and skin inflammation. Belly feather condition was worse for HIGH vs. LOW hens (Odds Ratio (OR): 1.61; 95% CI: 1.27-2.05; P< 0.001). Skin inflammation developed at 30 wk; HIGH hens were less likely to have active inflammation (OR=0.43, 95% CI: 0.21-0.86, P=0.016) and tended not to have skin lesions compared to LOW hens (OR=0.75, 95% CI: 0.54-1.03, P=0.074). LOW hens (1.93±0.01 kg) had higher BW than HIGH hens (1.91±0.01 kg, P=0.048). High mite infestation levels were associated with worse belly feather condition and lower BW, and little active skin inflammation. Ongoing research will examine infestation effects on hen behavior.