later ages suggest that selection of young mobile broiler chicks might increase activity at a later age and might therefore reduce the occurrence of leg abnormalities. q 2000 Elsevier Science B.V.
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Keywords: Broiler chicken; Locomotion; Walking; Genetic
1. Introduction
Leg weakness often results from non-infectious disorders of the skeletal system in Ž
. Ž
broiler chickens Thorp, 1994 , with numerous bone abnormalities tibial dyschon- .
Ž droplasia, tarsal angulation, femoral epiphysiolysis . Bone quality mass, shape, internal
. architecture is known to be influenced by the mechanical stresses that are applied to the
Ž .
bones Lanyon, 1992 . Increased levels of activity strengthen bones and reduce bone Ž
. deformities Reiter and Bessei, 1998 , whereas a lack of exercise can increase the
Ž .
incidence of leg abnormalities in broilers Haye and Simons, 1978 . Locomotor activity is a component of many behavioural patterns but it may have lost
part of its adaptive value for meat-type fowl in the present housing systems where heat, food and water are dispensed within easy reach. Selection for feed conversion has also
probably reduced the need or desire for energy consuming behaviours such as running or long walks, just as the aggressive behaviour has been affected by selection for high
Ž .
growth rate Mench, 1988 . Better knowledge of locomotor behaviour is needed in broiler chickens in order to counterbalance this trend and its dramatic consequences on
leg condition and welfare. This requires better understanding of how the behaviour develops, the motivations involved and which factors can enhance the pattern. Few
papers describe the ontogeny of locomotor behaviour because it is often associated with
Ž other patterns such as feeding, imprinting and social behaviour reviewed by Rogers,
. 1995 . In contrast, several authors have studied the factors modifying locomotor activity,
Ž .
especially during the finishing period 3–6 weeks . Using environmental manipulation to enhance activity in chickens has been widely examined, including increased floor area
Ž and modified stocking density Rodenhoff and Dammrich, 1971; Lewis and Hurnik,
¨
. Ž
1990 , increased distance between feeder and drinker Simons, 1986; Reiter and Bessei, .
Ž .
1996 , use of perches Hughes and Elson, 1977; Newberry et al., 1995 , light colour and Ž
. Ž
intensity Praytino et al., 1997a,b , forced displacements using fan movements Lei and .
Van Beek, 1997 . Genetic variability of locomotor activity has been much less studied. Differences in
Ž .
growth rate lead to modifications in feeding Boa-Amponsem et al., 1991 and in Ž
. locomotion Reiter and Bessei, 1997 , but it has not been established whether these
modifications are induced by genetic factors or by differences in body weight. In order to clarify this point, the behaviour of chicks was studied in the present experiment
during early life, when body weights are very close in genetic stocks with different growth rates. This starting period is very interesting because during this period the rates
Ž .
of bone growth and mineralization are highest Rose et al., 1996 , and therefore exercise can have a major strengthening effect on bone and be very effective in preventing bone
deformities. Furthermore, if early activity is related to the activity at a later age,
differences in activity during the starting period can be used as behavioural markers to select more mobile chickens.
2. Materials and methods
