Demand functions for cage size in rabbits selectively bred for high and low activity in open-field

Abstract

It was examined whether the divergent genetic selection for activity in open-field influences the motivation of rabbits to enlarge cage size, using operant conditioning technique. Twenty New Zealand White rabbits of both sexes, chosen randomly from two lines selected over nine generations for high (H, n = 10) and low (L, n = 10) locomotor activity in the open-field, were trained to press a lever to get access to more space by cage enlargement as a reinforcer. The demand functions were generated by plotting the achieved cage space (CS) as product of the number of enlargements × cage size at five increasing cage sizes, against the workload (fixed ratio (FR) = preselected number of lever pressing within 3 min, i.e. FR1, FR2, FR4 and FR8) using log–log-transformed CS and FR coordinates. To estimate the cage space demand, the total number of cage enlargements at given cage size was plotted against FR. All rabbits had learned to press the lever for food in the training phase. There was a non-significant tendency for more H than L rabbits and for more males than females to press the lever for cage enlargement when FR and cage size increased. The male H rabbits made on average more cage enlargements than the L rabbits of both sexes and the H females, resulting in more CS achieved and more area under the demand curve (differences non-significant). With increasing FR and increasing cage size classes, the rabbits did significantly less enlargements and thus achieved less CS ( P < 0.0001). The H males had the highest intercept and the L males had the lowest intercept and the shallowest slope, however, all the differences in characteristics of the demand functions between lines and sexes were non-significant. There were significant correlations between measures of motivation calculated from the demand function (baseline rate, total number of lever pressess, total cage size achieved, area under the curve, slope, intercept). The motivation for more cage space was negatively correlated with body weight. The percentage of animals that could be conditioned operantly have been suggested as the additional measure of differences in motivation between groups of animals. The results show that operant conditioning and demand function using the settings as in the present experiment could not demonstrate significant differences in motivation for more cage space in rabbits selected divergently for open-field locomotor activity.