Assessing the motivation of Leghorn hens to access outdoor space and pasture resources

The choice of suitable genotype, especially in free range poultry production, is crucial because it is strictly linked to the use of outdoor space. Accordingly, the aim of the present study was to evaluate the motivation of chickens to use outdoor pasture in comparison to feed. The feed, for all animals, represents a primary need ensuring nutrition of the organism; thus, feed could be considered a control test to compare the hen motivation towards different resources. To this purpose, 9 white Leghorns hens at 38 weeks of age (1.6 kg body weight) were housed in a pen equipped with a shelter (inside 10 hens/m2, outdoor 10 m2/hen). To reach the outdoor area, hens had to pay a cost by pushing through a one-way transparent weighted door. The door weight was 150 g and increased 100 g every 2 days. Each animal was identified by a ring provided with a chip. A monitoring system (ChickenGate), consisting in an antenna placed near the pushing door was used to record the animals which reach the resource. Results showed that for both the resources (pasture and feed) hens reduced the visit number as a consequence of the gradually increase of door weight. In particular, the maximum weight pushed by hens to reach the pasture was 650 g whereas 450 g for feed. However, independently from the resources, animals showed a great individual variability. Surprisingly, between the feed and grass resources, animals have a tendency to choose the grass. In fact, hens were available to pay a highest cost to access to the outdoor area and use the pasture resource. However, it is important to consider that hens, at equal weight, have performed higher number of visits to feed resource in comparison to pasture. This difference is probably due to the time of grazing and exploration of the outdoor area, as well as comfort activities such as sand baths, that require more time than the pecking the feed. This study showed that, despite the biological-physiological need for animals is the achievement of the feed, the motivation of the animals is stronger oriented to the pasture resource. This trend is probably justified by the fact that the grass resource provides a multitude of activities (feeds, kinetic and comfort behaviours) compared to the feed intake and it is surely affected by the breed used. It is widely known that the interest in outdoor is affected by the genetic strain; accordingly, the assessment of motivation could be useful also for differentiating genetic strain.