The influence of stocking density on the behaviour of featherless and normally- feathered broilers under hot ambient temperature

Problems of heat dissipation restrict feed intake and growth rate of conventional broilers under hot environmental conditions and high stocking density. Featherless broilers dissipate through the whole body surface, and, thus, are better adapted to high ambient temperatures. The aim of the present study was to compare the behaviour of featherless chickens and conventional feathered broilers under high ambient temperatures and increasing stocking densities. Three groups of featherless and normally feathered broiler type chickens each were kept in deep litter pens. The ambient temperature was kept between 33C. Stocking density was 16.6; 21.1 and 32.5 kg/m2 in feathered and 28.1; 35.9 and 45.6 kg/m2 in the featherless chickens. The temperature of the litter surface increased with increasing stocking density, regardless of the breed, from 31.4 to about 37 centigrade. The behaviour was recorded at 7 weeks of age using video-recording. Percent spent walking, standing, sitting, feeding, drinking, preening was recorded by time sampling technique. The duration of the same behaviours and of, panting was recorded by focal animal sampling. Within the feathered broilers, walking, standing, sitting, preening and drinking was reduced with increasing stocking density. Panting occurred in all groups and under all stocking densities. Bouts of panting were shorter in featherless than in feathered birds. The featherless broilers did not consistently respond to increasing stocking density in most behaviours. In some cases a similar trend in response to stocking density in behaviour occurred in featherless as in the feathered broilers, but at a higher density. The behavioural responses could be explained by the attempt of the birds to cope with high temperature. The results suggest that changes in behaviour in response to stocking density are caused by the temperature rather than physical restriction of space. It is concluded that at high ambient temperature featherless broilers show a better state of welfare than feathered broilers