Feed habituation alleviates decreased feed intake after feed replacement in broilers
In the present study, 2 experiments were conducted to investigate the effect of replacing a mash diet with a pellet diet on the expression of genes related to appetite in the hypothalamus and gastrointestinal tract (GT) and to evaluate the attenuating effect of feed habituation on the disadvantage influence on feed consumption. In experiment 1, the mash diet of one group of 21-day-old chicks was replaced with a pellet diet (PD) with the same ingredient composition, while the other group of chicks was continued on the mash diet (control). In experiment 2, all the experimental chickens were divided into 3 treatments at 18 d of age. One treatment of birds was provided with feeders with pellet feed scattered on the surface of the mash diet (around one-third of feeder surface, MP) from d 18 to d 20, and they were provided with the PD on d 21. The other 2 treatments of chickens were either fed with the PD (PDF) or continued the mash diet (control) at 21 d of age. The results showed that replacing a mash diet with a PD decreased (P < 0.05) feed consumption. The intestinal morphology was not influenced (P > 0.05). The mRNA levels of cholecystokinin (CCK) in the jejunum were upregulated (P < 0.05) in the PD chickens. The expression of anorexia gene ghrelin, corticotropin-releasing hormone (CRH), and melanocortin receptor 4 (MCR-4) were significantly down-regulated (P < 0.05) in the hypothalamus of the MP and PDF chickens 4 h after feed replacement. The results indicated that feed replacement altered the expression of genes related to appetite in the GT and hypothalamus. Pellet changeover causes a short-term decrease in the feed intake of broilers, and feed habituation relieves the negative effects of feed replacement.