Behavioural adaptation of laying hens to dilution of diets under mash and pellet form.

1. Two laying diets, control (A) and a low-energy (B) diet diluted by adding 450 g/kg wheat bran, were fed to semi-heavy hens in three different forms: mash, small pellets and large pellets. The behavioural adaptations and the production characteristics for these six regimens were studied on 72 individually caged hens, between 19 and 29 weeks of age, subjected to a lighting pattern of 14 h light/24 h. 2. Diet B, as mash, showed a lower apparent physical density than the others. The hardness and durability of the pelleted diets were similar. 3. Hens fed the mash diet B could not completely adjust their food intake to compensate for the dilution and showed reduced egg output and body weight gain compared to the other groups. 4. Video observation of each hen for 14 consecutive hours showed that mash-fed hens ate for longer periods than pellet-fed hens during the first 11 h (proportion of time spent eating: 41.3% mash B, 32.5% mash A and 20% to 25% for all the pelleted diets). These differences were less pronounced during the last 3 h of the photoperiod. 5. Trough-oriented stereotypies were noted in 14 out of 22 mash-fed hens and in 12 out of 47 pellet-fed hens. Dilution of the diet did not appear to exacerbate stereotyped behaviours under the conditions of the study. 6. This experiment demonstrates that the feeding behaviour of laying hens is affected by the physical characteristics of the diet and that this may lower their productivity. 7. Low-energy pelleted diets might be used to feed hens efficiently in tropical countries where cereal by-products are abundant.