The effect of weight load on the legs of broilers behaviour

The aim of the experiment was to study the behaviour of fast growing (FG) and slow growing (SG) broilers under the same weight load. For this purpose a harness and a suspension device were developed which alleviate a part of the weight load on the legs. The weight load in the SG birds was increased by fitting pieces of lead on the back and the breast. Using these methods the weight load of both lines was adjusted to the average weight of both lines. A total of 24 male broilers, 12 ISA S257 and 12 ROSS 308, were assigned to 4 groups of three birds each. One bird was weight adjusted, one was wearing the harness without weight adjustment and one was without harness. Duration and frequency of walking and resting behaviour were recorded. The torsional and angular deformity of tibiae were measured according to Leterrier (1992). The amount and thickness of the corticalis, bone density and area were measured at the middle tibia by computer tomography. The weight-reduced FG broilers showed higher activity in the 6th week of age. The weight-increased SG broilers showed less activity than the SG broilers without harness. The weight-reduced FG broilers showed similar activity as the SG broilers without harness. Total density and corticalis area were higher for the weight-reduced FG broilers than for the FG broilers without harness. The results show that weight load is the main influencing factor for differences in locomotor activity and resting behaviour of SG and FG broiler strains.