Sex and type of feed effects on motivation and ability to walk for a food reward in fast growing broilers

Abstract

Housing conditions, body weight, leg problems and pain influence behaviour of broilers. Apart from the physical ability, little is known about the motivation to perform behaviour. The distinction between motivation and ability is relevant as a lack of motivation has consequences for the interpretation of, e.g. the observed immobility in terms of compromised welfare. A runway experiment with fast growing broilers was conducted to investigate the influence of sex and type of feed on motivation and ability to walk for a food reward (mealworm) without depriving the birds from feed before testing. Twenty-four males and 24 females fed with two types of feed, conventional or free-range (less energy and protein) feed, were individually tested in a 2 m long runway from four to seven weeks of age. Five bowls were placed in the runway, one at every 40 cm. Three sessions were applied within 1 week (1) control session: each bowl contained one mealworm; (2) frustration session: the first four bowls were empty, the last bowl contained five mealworms, and (3) obstacle session: each bowl contained one mealworm and 10 cm high obstacles were placed between the bowls. Weekly, body weight and feed consumption were measured and gait score was assessed of each individual. Over all weeks, birds walked faster in frustration sessions than in control or obstacle sessions and faster in control than in obstacle sessions. Birds sat more in obstacle than in control sessions, indicating that ability to walk was affected by the difficulty of the task. Males walked faster in control and obstacle sessions than females, despite the higher body weight. The number of vocalisations in the runway decreased over time and males vocalised more than females. In both sexes, free-range fed birds vocalised more than conventionally fed birds. Differences between frustration and control sessions and obstacles and control sessions at individual level within a week were also measured, called the motivation and the ability effect. Concluded is that sex and type of feed have effects on different measures in the runway. Male broilers walked faster to a food reward and vocalised more than females. The role of type of feed was ambiguous. It did not influence body weight, walking speed or gait score, but conventionally fed birds sat more and had a higher latency to leave the start box and to reach the last bowl, and free-range fed birds vocalised more. No sex or feed differences were found for the motivation and the ability effect. That means that frustration and obstacles had similar impact on both sexes and both types of feed and that sex differences in walking speed probably were a result of physical differences (males are stronger and bigger).