Feed composition and hardness interact in preference and intake in chickens
Résumé
Chickens prefer high- to low-energy feed in the long-term when they have previously experienced both of them for several days. However, high-energy pellets can also be softer than those with low energy. The present study aimed to understand whether this preference for high-energy feed was influenced by pellet hardness. Male broiler chickens received either a complete diet (2980 kcal/kg ME) or, alternately a low (L) energy diet (2800 kcal/kg ME) on day I and a high (H) energy diet (3160 kcal/kg ME) the following day of the cycle. Feeds also differed in the hardness of the pellets: firm (F) or soft (S). Five treatments were compared from D10 to D25: (1) C: complete diet (medium hardness), and four treatments with a sequential feeding schedule (S), (2) S(FF): LF followed by HF, (3) S(FS): LF followed by HS, (4) S(SF): LS followed by HF and (5) S(SS): LS followed by HS. Total feed intake was measured during the whole sequential feeding period and consumption kinetics were measured for the 1st, 4th and 8th cycles. Short-term preferences were then evaluated with a short choice test in chickens either (1) fed with the same feeds as during the SF period or (2) fed pellets with the reverse hardness to that of the SF period: S instead of F, and F instead of S. All the chickens under-consumed the low-energy diet during the first 15 min of the fourth and eighth cycles, but feed intake was similar between treatments over a 24-h period. During the choice test, all groups given the same feed as during sequential feeding (SF) preferred the high-energy diet whatever the hardness of the pellets tested. Moreover, preference for the high-energy diet increased when associated with hard pellets. These preferences remained when chickens were given pellets with the opposite hardness to that of the sequential feeding period. These results suggest that in the short-term, experienced chickens were able to discern energy content in feeds differing in hardness and preferred high-energy feed. During the sequential feeding period and choice test, the preference for the high-energy feed was enhanced when high energy was associated with hard pellets. This preference was not related to a higher daily intake which clearly suggests short- and long-term feed choices are regulated differently. (C) 2009 Elsevier B.V. All rights reserved.