Abstract
In a two-year experiment, we investigated the influence of sward plant species composition (sward type), stocking duration and state of sward degradation on the foraging behaviour of chickens. Laying hens (ISA Warren) were pastured on 15 sward types including 14 monocultures of grassland plant species (nine grasses and five forb species) and one mixed sward of the 14 species for three levels of stocking duration (one, two and three days). The behavioural traits pecking plants, ground pecking and scratching were recorded by scan sampling. Sward type had a significant effect on scratching, plant pecking, and total sward-directed pecking (plant and ground pecking together) in the grass swards (p < 0.01), and on ground pecking in the forb swards (p < 0.05). With prolonged stocking, the frequency of ground pecking significantly increased, whereas that of scratching, plant pecking and total sward-directed pecking significantly decreased. There was a significant stocking duration × sward type interaction for all of the observed behaviours (p < 0.01). The tested sward types differed strongly with respect to the extent of degradation resulting from the fixed levels of stocking duration. Sward degradation as measured by percentage ground cover of green leaves or stolons and stems had a significant effect on ground, plant and total sward-directed pecking in forb swards (p < 0.001). Considering the observation of other studies that the presence of vegetation and a good use of the run benefit animal welfare by reducing the incidence of feather and injurious pecking, the results of this study may be relevant for the design and management of swards for laying hens outdoor runs and for a welfare-oriented optimization of husbandry systems.