Feed-restricted broiler breeders: state-dependent learning as a novel welfare assessment tool to evaluate their hunger state?

This paper reports three experiments that aimed to validate the use of state-dependentlearning (SDL) as a novel welfare assessment tool to evaluate the hunger state of feed-restricted broiler breeders.In each experiment, birds alternated every 2 days between two food rations: quantitativefeed restriction (QFR) and ad libitum access to the same feed (AL). Each food ration waspaired with a different, end of day, coloured food reward. It was predicted that the rewardassociated with hunger (QFR FR) would be preferred to the food reward associated with AL(AL FR) in a subsequent choice test. The SDL preference testing took place after 4 and 8 daysof training. Each bird was tested twice (once per food ration fed on the test day).In experiment 1 (pilot, n = 4), birds preferred the QFR-associated reward during both tests(mean (±S.E.M.) preference: QFR FR: 35.0 (±3.5) g; AL FR: 2 (±1.3) g, but differential foodreward intake between hunger states during training confounded the results.In experiment two (n = 12) a smaller food reward was used during training to try andequalise intake. The birds preferred the QFR FR in test 1 only (least significant differ-ence (L.S.D.) = 15.08, P < 0.05). The mean (±S.E.M.) consumption in test 1 was: QFR FR: 31.6(±4.3) g; AL FR: 9.41 (±2.3) g. However, differential reward intake continued to confoundthe findings.In experiment three (n = 8), the food reward was made more palatable by feeding moistand food reward intake during training was equalised between hunger states. During test-ing, birds continued to show a significant preference in test 1 only (L.S.D. = 13.73, P < 0.05).It was concluded that SDL-derived preferences observed do exist but are not a robustphenomenon. Therefore, further research is needed to quantify factors influencing SDLdevelopment and maintenance before using SDL as a tool to assess hunger in feed-restrictedbroiler breeders.© 2015 Elsevier B.V. All rights reserved.