Risk factors for navigation ability of laying hens at housing in an aviary system

To evaluate the risk factors for navigation ability of two genotypes of laying hens at housing in an aviary system, 1,800 pullets, half Lohmann White-LSL and half Hy-line Brown, were randomly allocated at 17 weeks of age in 8 pens of an experimental aviary (3 tiers), according to a bi-factorial arrangement, 2 genotypes (brown vs. white hens) × 2 types of pens (enriched or not enriched with additional perches). Data collected by video-recording at 17 and 20 weeks of age were used to assess the number of successful and unsuccessful landings from any part/equipment of the aviary to the floor. Risk factors related to failed landings were evaluated by multivariate logistic regression analysis through a forward stepwise selection using the PROC LOGISTIC of SAS. The regression coefficients were expressed as odds ratio (OR) with 95% confidence interval (CI). Compared to brown hens, white hens performed a significantly higher number of landings per hour in the observation interval (80.7 vs. 35.4; P<0.001) with a higher success rate (94.8% vs. 88.6%; P<001). Brown hens had higher odds of failed landings compared with white hens (OR: 6.65; 95% CI: 4.36-10.1). The logistic regression analysis showed significantly higher odds (OR: 1.90; P<0.001) of experiencing failed landings at 17 weeks compared to 20 weeks. No significant difference in the number or in the rate of success of landings was recorded between enriched and not enriched pens, where the logistic regression analysis only measured a trend (OR: 1.29; P=0.09). The odds of failed landings were greatly higher when comparing long with medium flight distance to floor (i.e. hens starting from the third vs. the second tiers of the aviary) (OR: 31.1; P<0.001) and lower comparing short (i.e. hens starting from the first tiers of the aviary) with medium flight distance (OR: 0.17; P<0.001). In conclusion, under the condition of the present study, white hens exhibited higher navigation activity and ability compared to brown hens since the first week after housing; the navigation ability improved four after housing weeks; the enrichment with additional perches played a minor role. Long-term effects on space use should be evaluated over the laying period.