Stimuli from feed for sham dustbathing in caged laying hens

Abstract

Sham dustbathing is observed in caged hens, particularly near the feed trough, so it seems that feed acts as a stimulus for this behaviour, and the aim of this experiment was to test this. Commercial White Leghorn pullets that had been reared in group cages were housed at 17 weeks of age in furnished cages with a floor of wire mesh, perch, and laying nest lined with artificial turf. Four groups of three hens, originating from four furnished cages, were used in six experiments starting at 65 weeks of age. For each experiment, two groups were used as controls (with 300g of mash feed) while the other two were tested with a new feed stimulus for two days, then the treatments were switched so that all groups experienced both. The stimuli were (1) empty feed trough; (2) feed covered with transparent lid; (3) feed in raised trough; (4) extra feed (1050g); (5) powder feed (particles smaller than 2mm); (6) granule feed (particles 2mm or bigger). It seemed that visual and physical contact with feed induce not only foraging, but also bill raking, an initial element of sham dustbathing. Low frequencies of bill raking and few or no sham dustbathing bouts were observed in treatments (1)–(3), where feed was absent or not easily accessible for the hens, thus, visual and physical contact with feed at or near ‘ground level’ seemed to be important to perform sham dustbathing. Sham dustbathing increased and all hens performed it in treatment (4) when hens had extra feed and (5) with powder feed; more bill raking was observed, and the other elements of sham dustbathing also increased. Sham dustbathing decreased in treatment (6) with granule feed. In control treatments, low ranked hens performed fewer sham dustbathing bouts than higher ranked hens. Interruptions to sham dustbathing by other hen were most frequent in low ranked hens (34%) and least frequent in high ranked hens (0.5%). However, low ranked hens sham dustbathed more often in treatment (4) with extra feed than in controls. The results suggested that feeding, foraging, and sham dustbathing reinforced each other, with extra feed stimulating sham dustbathing, including in low ranked hens. As feed is a typical and unique stimulus, sham dustbathing with feed may be one of hen’s coping strategies to adapt to their housing in cages when they do not have an appropriate dustbathing substrate.