THE EFFECT OF A SINGLE OR REPEATED PERIOD OF HIGH STOCKING DENSITY ONTHE BEHAVIOR AND RESPONSE TO STIMULI IN BROILER-CHICKENS

Broiler chickens are normally housed at a fixed number per unit area t hroughout their life, which reduces their opportunity for movement dur ing the later stages of rearing. An experiment is described that expos ed broilers to a high stocking density either once or twice in the rea ring period, and investigated the effects on the birds' behavior, and the response to other birds and humans after the second exposure to hi gh or low stocking density. The stocking density was increased from a low level (1.7 kg/m(2)) to a high level (14 kg/m(2)) for the 2nd and/o r 4th wk of rearing, or left unchanged at the low level. When stocked at the low rate, the birds spent more time walking and sitting and les s time dozing and sleeping. They pecked more at inanimate objects and interacted more with other birds, but this did not include aggressive interaction. The effects of stocking density on behavior were greater in Week 4 than in Week 2, but there was no evidence that exposure to a high stocking density in Week 2 influenced the birds' behavioral resp onse to a high stocking density in Week 4. Where stocking density did affect behavior in both Weeks 2 and 4, there was evidence of the respo nse being cumulative. The activity of birds in the presence of another bird restrained in an open field arena was greatest when they had bee n stocked at the low density throughout the experiment. When a familia r person was in the arena, the birds that had been stocked at the high density in Week 2 were most active, but these birds showed the longes t tonic immobility when inverted in a cradle. It is concluded that a h igh stocking density reduces activity in broiler chickens, and that bi rds stocked at a high density early in the rearing period are most act ive in the presence of people and show the longest tonic immobility in response to a fearful stimulus.