differences in activity during the starting period can be used as behavioural markers to select more mobile chickens.
2. Materials and methods
2.1. Birds The study comprised two experimental groups: 30 male broiler chicks from a fast
Ž .
growing genetic stock B, IJV 915, Institut de Selection Animale, Lyon, France and 30
´
Ž .
male ‘‘label rouge’’ chicks L, T551, SASSO, Sabres, France from a slow growing genetic stock. Chicks were provided by the same commercial hatchery. There were six
replicates for each treatment. Five birds from each stock were randomly assigned to each replicate. They were wing banded at hatching and weighed. All birds were reared from
hatching to 22 days of age. Very low stocking densities were used because total potential activity needs to be described without overcrowding effects. Low densities
enabled us to identify all individuals in order to study interindividual correlations and facilitate behavioural observations. Each group was kept in a 2 m
2
floor pen covered Ž
2
. with wood shavings density s 2.5 birdsrm . Each pen contained one drinker and a
1-m-long feeder. To avoid spillage the food was covered with a wire mesh until the chicks were 10 days old. The lighting schedule was 24 L. Chicks were fed a standard
Ž diet
metabolizable energy s 12.98 kJ, crude protein s 22, Ca s 0.15, available .
P s 0.42 . Food was provided in the form of mash during the first 3 days of life. From Ž
. 3 to 7 days of age, mash and pellets diameter s 2.5 mm were mixed. Only pellets were
provided from day 8. Food and water were available ad libitum. At 17 days of age, every chick was individually observed in the pen in order to detect early lameness. At
Ž .
the end of the experiment day 22 , each individual was weighed and abnormal tarsal Ž
. Ž
. angulations were detected varus or valgus , according to Leterrier and Nys’s 1992
classification. 2.2. ObserÕations
Four birds were chosen at random from each pen at the beginning of the experiment Ž
. and identified by colours red or blue marks on the head or the body , the fifth was not
marked. Birds were marked again when necessary throughout the rearing period. The observer sat 2 m above the birds and 50 cm back from pens during observation. Chicks
Ž .
were observed by scan sampling and focal sampling Martin and Bateson, 1986 . All observations were made by the same observer.
2.2.1. Scan sampling At 1, 8, 15 and 17 days of age, each floor pen was scanned for 90 min. The number
Ž of individuals which expressed each category of behaviour standing, eating, drinking,
. walking or lying was recorded every 2 min. The categories were exclusive, so a
standing bird was neither eating nor drinking. The observer noted ‘‘eating’’ when a bird pecked food in or around the feeder. A bird was considered to be ‘‘drinking’’ when it
Ž .
had its beak in water or stood in front of the drinker with raised head swallowing . The number of ‘‘active immobile’’ chicks was calculated as the sum of the birds standing or
eating or drinking.
2.2.2. Focal sampling Ž
. Since chickens lie for 80 to 90 of their time Bessei, 1992 , only behavioural
patterns expressed during the ‘‘standing’’ bouts were recorded, i.e. behaviours expressed from the moment when a bird stood up until it lay down. The observations were sampled
Ž .
during four periods of 2 days 2–3, 6–7, 13–14, 20–21 days after hatch . About 10 behavioural bouts were recorded per pen and per day of observation. Behaviours were
Ž .
recorded using the Observer 3.0 Noldus Information Technology, Netherlands . This Ž
software records duration of the different states walking, running, standing, eating, .
Ž drinking, preening and exploring litter and occurrence of the different events each step
. and interaction with a congener . A bird was considered to be walking only when it was
mobile ; when it was walking step by step, short periods of immobility were recorded as standing. Eating and drinking were considered to have stopped as soon as the bird stood
inactive, even if it was in front of a feeder or a drinker. Exploring litter included pecking and scratching the floor. Preening contained feather licking and scratching itself. The
Ž .
term interaction was used for behaviours antagonistic or not which involved contact between the interacting pair during the standing bouts: pecking, leaping, sparring,
preening each other and stepping on another bird. For analysis, standing bouts were sorted into two types: feeding bouts in which
Ž .
chicks drank or ate and other bouts non-feeding bouts . These two types of bout were analysed separately because the motivation for activities in each kind of bout was
believed to be different.
2.3. Data analysis For all data analysed, the pen was the experimental unit. Pen means were therefore
used to examine the effects of age and genetic strain. Because data were not normally distributed, they were analysed with nonparametric statistical tests using Statview 4.05.
Genetic effects were tested with the Mann–Whitney U test, and age effects for each strain using the Friedman test. Feeding and non-feeding bouts were compared using
Wilcoxon test. The correlation coefficients between body weight and the different behaviours at different ages were computed using Spearman’s rank correlation. For focal
sampling, we chose to eliminate from analysis the birds which were lame at day 17 Ž
. Ž
n s 5 in order to avoid any possible effect on general activity Weeks and Kestin, .
1997 .
3. Results
