Effect of ramps on space use of laying hens in a cage-free system

The effect of the presence of ramps in a three-tiers aviary system was evaluated on space use, as for animal distribution and egg laying position, and animal welfare, as for the occurrence of foot pad and keel bone lesions. To this purpose, 1800 Hyline Brown laying hens were housed in 8 modules (each with 225 hens), half with two ramps (one between the ground and the first tier; one between the second and the third tiers) and half without, and controlled from 18 to 47 weeks of age. Data were submitted to analysis of variance using a model with the main effects of the presence of ramps and the weeks of age (when relevant) and the PROC MIXED or GLIMMIX of SAS, depending on the data distribution; the module was used as a random effect. As for animal distribution measured once a week by direct observation around 11 a.m., the presence of ramps significantly decreased the number of hens on the first tier (28.1% to 22.3% of observed hens), the third tier (11.3% vs 8.71%), and the perches of the first tier (3.01% vs 2.85%), while increasing the number of animals observed on the ground and the second tier (4.92% to 5.11%) (P<0.001), this latter where nests were located. Accordingly, in modules with ramps, more eggs were laid in the nests (97.8% vs. 97.1% of total eggs) and less eggs were found on the wire nets of the third tiers (0.33 vs. 1.16%) (P<0.001). As regards foot pad and keel bone lesions, on average of all observations, no significant effect of the presence of ramps was recorded on their occurrence which significantly increased with age (foot pad lesions from 0% to 31.5% and keel bone lesions from 1.75% to 24.5% from 21 to 47 weeks of age). Nevertheless, when foot pad lesions firstly appeared (i.e. week 30) due to a degradation of litter quality because of unsuitable management of ventilation inside the barn, their occurrence was lower in hens kept in modules with ramps compared to those without ramps (19.3% vs. 28.9%; P<0.01). In conclusions, the presence of ramps facilitated the displacements of hens between the third and the second tiers of the aviary which increased the use of nests for laying; additionally, the displacements between the first tier and the ground were facilitated which potentially could increase opportunities for comfort behaviours, such as dust bathing in the litter, on one side, and the possibility of moving away from the litter when conditions are not optimal, on the other side. PNRR I.3.3 innovativi (CUP: C96E23000010005) funded the PhD grant of Mattia Pravato.