The push-door for measuring motivation in hens: An adaptation and a critical discussion of the method

Animals should be given the opportunity to perform behaviours that they are motivated to show if we are to maximise their welfare. Research studies into motivation and appropriate methods of studying it are therefore important. Different factors may need to be taken into consideration depending on the form of the behaviour being studied. Certain commodities, such as a perch for night-time roosting, have a value only if the animal is given full access to them until it has completed the behaviour. For other commodities, such as food and water, the amount can be varied along a continuous scale without affecting the animalsí demand for that resource. The commonly used operant techniques generating demand curves are based on the assumption that demand is not affected by the size of the reward (ie how much of the commodity the animal gains access to). As a consequence, these techniques are appropriate only for assessing motivation for resources of which the size can be varied. Resources of the ëall-or-noneí type, on the other hand, require a different approach. We discuss different adaptations of the push-door technique as a measure of motivation, and we present results that validate a version with fixed, individually adapted levels of resistance. The method was validated using laying hens (Gallus gallus domesticus) tested at different levels of food deprivation and exposed to two series of increasing door resistances. The results show that the level of food-deprivation affects the amount of resistance that is overcome. We conclude that this method could be used to study hensí motivation for commodities of the ëall-or-noneí type.