Effects of development and delayed feed access on ghrelin expression in neonatal broiler chickens

Two experiments were conducted to study the effects of development and delayed feed access on ghrelin expression in neonatal chickens. In experiment 1, ghrelin levels in ad libitum-fed chickens were assessed from hatching (0 h) to 120 h. Ghrelin mRNA expression increased after hatching and reached peak levels at 24 h; levels were 1.8-fold higher compared to those at 0 h. Afterward, ghrelin expression decreased consistently throughout the later experimental period, and at 120 h, it was only 16.0% of 0 h levels. The density of ghrelin immunopositive cells in the proventriculus and plasma ghrelin levels decreased slightly from hatching to 48 h and later increased slowly until the end of the experimental period. In a follow-up study, chickens were assigned randomly into 2 groups after hatching, a control group ( C: , fed ad libitum) and a delayed feeding group ( F+SF: , 72-h fast period, subsequently fed ad libitum). Delayed feed access for 72 h up-regulated ghrelin mRNA expression significantly in the proventriculus (P < 0.05) to 2.1-fold higher levels compared to the control, while the density of ghrelin immunopositive cells and the plasma ghrelin level decreased (P < 0.05) to 28.4% and 64.8% of the control, respectively. After the onset of feeding, the ghrelin mRNA expression in the delayed feeding group was decreased but still higher than that of the control (P < 0.05). The density of ghrelin immunopositive cells and the plasma ghrelin level climbed quickly and all returned to the control level with a supply of food for 48 h. These results suggest that the onset of feeding in neonatal chickens stimulated an increase in ghrelin peptide levels and that ghrelin peptide levels increased with age. Neonatal chickens respond to food deprivation in a different way than do young and adult chickens.