Funder and dates: Defra, July 2009- Dec 2012
Collaborators/partners: SRUC, Roslin Institute, University of Newcastle and BioSS
At any one time in the UK, there are approximately 7.5 million broiler breeder chickens. Although some degree of feed restriction occurs during lay (when they are aged between 21 and 60 weeks), restriction during rearing (0-20 weeks of age) is more severe, providing only 40% of the feed that a broiler breeder of similar weight could eat, and this period is the focus for the work in this project.
There is good evidence showing that restricted feeding of broiler breeders results in hunger. However, feeding these birds ad libitum results in reduced productivity and various health and welfare problems, including multiple ovulations, thermal discomfort (panting), reduced immunocompetence, and skeletal and metabolic disease resulting in higher mortality. This conflict between hunger caused by restricted feeding and these other welfare problems under ad libitum feeding has been referred to as a ‘welfare dilemma’ or as the ‘broiler breeder paradox’. A major issue in resolving this dilemma is a lack of understanding over the severity of the psychological challenge that feed restriction poses to the broiler breeder to balance against the physical problems that arise through ad libitum feeding. This was evident in a judicial review of the practice of feed restriction when the judge expressed himself as uncertain as to the meaning of hunger for broiler breeder chickens (CIWF vs Defra 2003). This project’s aim was to provide objective information on the subjective experiences of feed restricted broiler breeders in a way that would allow policy makers and others to better equate the different challenges facing broiler breeders and provide a better evidence base for resolving the dilemma.
Conditioned Place Preference (CPP) or Aversion (CPA) methods are potentially useful tools in animal welfare assessment because they permit measurement of the reinforcing properties of a stimulus in the absence of the stimulus itself. We used CPP/CPA techniques in a series of experiments to assess the preference of food restricted broiler breeders for increased food quantities or avoidance of aversive stimuli. However the broiler breeders were rarely successful in forming a CPP/CPA and furthermore, where statistical significance was achieved for CPP the preferences shown were very small. The most consistent result was a strong preference for the pen side birds were not previously housed on immediately before each test. It appeared that birds were motivated to explore a location where they had not just been housed in an attempt to find food and this motivation seemed to overshadow other effects. This result led to development of a novel motivation test to assess hunger.
One approach to measuring hunger is to observe how much birds will work, such as pecking a key, for access to more or different types of food. However, the sight, smell and feedback from consumption of the feed reward changes the context and may artificially raise feeding motivation. To avoid this, we tested broiler breeders in an apparatus in which they could work for access to a wooden platform covered in wood shavings by crossing a water runway which increased in length and depth in 8 successive tests. In the wood shavings area, they could perform exploratory and foraging behaviour (the appetitive phase of feeding) but were never rewarded with feed. Overall, birds fed commercially restricted levels (R) worked harder to reach the wood shavings area (reached it in a larger number of tests) than 2xR and 3xR birds. More restricted birds took less time to reach the area (R<2xR<3xR) and spent more time foraging while there (R>2xR>3xR). This indicates that restricted-fed birds were hungry and willing to work for the opportunity to forage even though food was never provided, suggesting that their motivation to perform the appetitive component of feeding behaviour (foraging/food searching) was sufficient to sustain their response. Thus food restriction in broiler breeders is a welfare concern and these methods could be used to test alternative feeding regimes to attempt to find ways of alleviating hunger while still maintaining healthy growth and reproduction in these birds which is explored in our BBSRC project.
From a physiological perspective, AGRP and NPY expression in the basal hypothalamus was significantly increased by chronic feed restriction but only AGRP mRNA levels reflected recent feeding experience: broiler breeder females at the same body weight that had been recently been on ad lib. feeding showed lower expression than restricted birds. This shows that AGRP mRNA not only reflects differences between a bird’s weight and potential weight or set point, but also discriminated between differing feeding histories of birds at the same body weight. This measure has also been integrated into our current BBSRC grant and will be measured on the same birds that behaviour data is collected from.
For more information about this research, see links to publications below or contact Dr Laura Dixon.