Intermittent fasting in chickens : Physiological mechanisms and welfare implications for broiler breeders

Broiler breeder chickens are the parent stock used to produce broiler chickens raised for human consumption and have long been caught in a welfare dilemma. The immensely successful selection of fast-growing meat-type chickens over the last 80 years has created a remarkably efficient meat-producer and given us access to cheap chicken meat but has also created health problems for the animals. These problems especially affect the breeder generation, which must be raised with strict feed restriction to limit weight gain and thus maintain physical health and normal fertility. At the same time, however, feed restriction causes chronic hunger and feeding frustration with reduced animal welfare as a result. In the EU alone 60 million breeders are affected annually and although the problem is well-known within the industry, there is financial incentive to keep selecting for even higher growth potential in broilers, further increasing the problems for broiler breeders. Many strategies for reducing the impact of growth restriction on breeder welfare have been suggested and are usually aimed at somehow increasing the amount of feed given at feeding times. This can be done either through adding bulky fibers to the diet or by reducing feeding frequency. In this thesis, focus is on the latter as we explore the effects of intermittent fasting (IF) on the welfare of young broiler breeders as well as wild-type Red Junglefowl. Intermittent fasting, or “skip-a-day” feeding, is supposedly the most common feeding strategy for broiler breeders worldwide but is perceived as welfare-reducing and thus illegal in Sweden and several other European countries. In spite of this, the scientific knowledge of how this type of feeding affects chicken welfare is scarce. Assessing the overall effect of IF on breeder welfare is complicated by large variations in both physiological and behavioral parameters between feeding and fasting days, but it does appear that chicken welfare is improved at least on the feeding days of IF regimens. It also seems that some of the health benefits reported from mammalian studies of IF may apply to chickens as well, although behavioral indicators still point to welfare issues unless the level of feed restriction can be relaxed. In comparison with daily feed restriction, IF appears to increase the motivation for feed consumption but to reduce the motivation for appetitive behaviors such as foraging, which may explain why birds fed on this type of schedule are often reported as calmer