Avian gait analysis
Corr, Sandra A.
Modern broilers have difficulty walking, and there is ongoing debate as to whether the birds are in pain. Most gait analysis of poultry consists of visual assessment and scoring, and the results are therefore very subjective. In order to describe and quantify gait patterns accurately, a more objective method is required. Only then can differences between the gait of normal chickens and modem broilers be properly described, and attempts made to determine whether the observed gait patterns are the result of the conformation of the birds, or the presence of pain.Two methods were used in this research. The pedobarograph is a relatively novel method of gait analysis for animals which enables footfall patterns to be recorded, enabling spatial parameters (step length, width and angle) and plantar pressure patterns to be described and measured. A Kistler force plate was then used to measure the three - dimensional ground reaction forces (GRF's) produced during walking. Speed and cadence can be calculated using either system.Gait patterns are described for normal birds, and for different strains of broilers, raised on different feeding regimes. All the gait parameters were very variable, both between birds, and within the same bird, even when bodyweight and speed were controlled for. Despite the high variability, however, significant differences were identified in many of the gait parameters between the different groups.The vertical and craniocaudal GRF's of Brown Leghorns showed similar characteristics to those produced in human walking. The peak vertical forces were of a similar order of magnitude in the birds as in humans (125 -150 % bodyweight), and the peak craniocaudal forces, and rate of change of force, were closely tied to speed. All the GRF's in the birds increased significantly with increasing speed, except for braking rate (which was more variable) and stance time (which decreased significantly). The mediolateral forces were much greater in the birds than have been reported for other species, however, with peaks of 10 -22% bodyweight. Analysis of plantar pressures showed that the pressures were concentrated on the digital pads, with the lowest pressures on the metatarsal pad ( <131 kNm "2), and highest pressures on the medial toe (up to 218 kNm "2).Combined gait analysis and morphometric studies of ad libitum -fed selected broilers identified many ways in which their gait deviated from that of relaxed broilers and Brown Leghorns, in ways which would serve to increase stability and decrease stresses on the skeleton. The ad libitum -fed selected birds (compared to restricted -fed strain -mates and relaxed birds of the same weight), had more breast muscle anteriorly, and shorter, wider legs, but with immature bones, of lower % ash content. They moved more slowly, taking short steps, and positioned their feet wide apart and turned `toe -out' to increase their walking base. They kept their feet on the ground for longer, with short swing periods, and long double contact times. Decreasing the unstable periods of single support, and increasing the stance periods, reduces the peak forces on the skeleton. The slow speed and short steps also reduce the vertical excursions of the centre of gravity. The very wide walking base results in abnormally large mediolateral forces being required to move the centre of gravity over the stance leg, however, increasing the inefficiency of the gait, leading to fatigue. Mediolateral forces in ad libitum -fed selected birds averaged 17 -21% bodyweight at 6 weeks, compared to 10 -11% in the Brown Leghorns, and <5 -8% in humans (Biewener, 1992).Changes in the GRF's were also demonstrated in the slower growing (restricted -fed) broilers with age. In these birds, both the peak vertical forces and the peak mediolateral forces decreased with age, despite the fact that the birds increased in size (and girth) and their speed of movement remained similar. This indicates that the birds developed gait optimisations as they grew (as is the case with children), possibly because the slower growth allowed the body to develop more in proportion.Analysis of the gait of a small number of lame birds demonstrated marked differences in the spatial and force parameters between the sound and lame limb. The peak forces on the lame leg were dramatically reduced, and compensatory increases were seen in the GRF's of the sound limb. The birds used several methods to avoid fully loading the lame leg: flapping the wings to raise the centre of gravity, pushing up on the sound limb prior to placing the lame leg down, and flexing the lame limb as it starts to weightbear.There were no changes in the GRF's or temporal parameters of gait of broilers given analgesic (carprofen). Unfortunately, this does not prove conclusively that the birds were not in pain, as analgesic efficacy has not been validated in broilers, and it is also possible that the parameters under test do not change in the presence of pain. However the incidental finding of old blood in synovial fluid samples of over 50% of the ad libitum -fed broilers adds to the welfare concerns. A second interesting finding was the high alkalinity of the fluid (median pH 8.15 - 8.40), with the possible consequences on intra- articular pharmacodynamics. Although the analgesic study proved inconclusive, results of the gait and morphometric studies demonstrate that it is possible to explain the gait patterns of ad libitum -fed selected broilers based on their body conformation alone.