Dixon, L., Dunn, I., Brocklehurst, S., Baker, L., Boswell, T., Caughey, S., Reid, A., Sandilands, V., Wilson, P. and D'Eath, R.
||Broiler breeder chickens are commercially feed restricted to slow their growth and improve their health and production. However, there is a growing body of literature demonstrating that this leads to chronic hunger resulting in poor welfare. However, a challenge in these studies is to account for possible daily rhythms or the effects of time since last meal on behavioral and physiological measures relating to feeding, appetite and hunger. To address this, we used 3 feed treatments: AL (ad libitum fed), Ram (restricted, fed in the morning) and Rpm (restricted, fed in the afternoon) to control for diurnal effects. We then conducted foraging motivation tests and collected home pen behavior and physiological samples at 4 times relative to feeding throughout a 24 h period. The feed treatment had the largest influence on the data, with AL birds weighing more, having, on average, lower concentrations of plasma NEFA, and lower mRNA expression of AGRP and NPY alongside higher expression of POMC in the basal hypothalamus than Ram or Rpm birds (P<0.001). R birds were more successful at completing the motivation test, had a shorter latency to complete the test, and did more walking and less feeding than AL birds in the home pen (P<0.01). There was little effect of time since last meal on many measures (P>0.05) but AGRP expression was highest in the basal hypothalamus shortly after a meal (P<0.05), blood plasma NEFA was higher in R birds just before feeding (P<0.001) and glucose higher in Ram birds just after feeding (P<0.001), significant effects were seen on some of the organ weights (P<0.001-<0.05), and the latency to complete the motivation test was shortest before the next meal (P<0.05). Time of day effects were mainly found in the difference in activity levels in the home pen when the lights were on (birds were more active) and lights off (birds were less active) periods, although there were effects of feed treatment on some behaviors. In conclusion, many behavioral and physiological hunger measures were not significantly influenced by time of day or time since the last meal. For the measures that do change, future studies should be designed so that sampling is balanced in such a way as to minimise bias due to these effects.