Mechanisms Of Glucocorticoids Regulating Food Intake In Broilers

To investigate the effects and mechanisms of stress on appetite of broilers(Gallus gallus domesticus), exogenous glucocorticoids was used to mimick stress on two phases of stress development of broilers. Changes of metabolism and mRNA expression level of important genes in appetite regulation in hypothalamus were measured and analyzed, in order to providing countermeasures for reforming energy waste in broiler chicken production.In part 1, there are 3 trials in experiment 1. In trial 1, 64 male broilers (Arbor Acres) with similar body weight were divided into 4 groups randomly, rearing in separate cage in which there were two containers with the color of red and green relatively. In group1, animals were stressed and diets were be at choice (DEX, high and low energy diet, n=8). In group 2, treats were the same as in group 1 except that dexamethasone was displaced by saline. In group 3, diets were all high energy(ME, 15.1KJ/kg; CP, 20%) (n=8), while diets were low energy (ME, 10.9KJ/kg; CP, 20%) in group 4(n=8); In trial 2, 96 AA broilers with similar body weight were divided into 6 groups randomly. On the basis of trial 1, there were two more groups in which the containers were noncolored (DEX, high, low energy diet; control). In trail 3, 32 AA broilers with similar body weight were divided into 2 groups. The treatments were the same as the container-noncolored groups in trail 2. All the broilers in this experiment were stressed by subcutaneous injection of DEX with a dose of 2.6mg/kg BW at 8:00 from 5 to 10 days old. Saline was injected with a suitable dose in the control group. During the trial, food intake was noted every day. At the day of 10, blood was obtained. The results showed that, stress was induced successfully and it increased the high energy diet ingestion, however, the body weigh was decreased significantly. All of these suggest that stress alters the appetite of broilers; there was no significant effect of color on food intake. In experiment 2, 96 AA broilers with similar body weight were divided into 6 groups: A (DEX, high energy diet), B (Saline, high energy diet), C (DEX, low energy diet), D (saline, low energy diet), E (DEX, diets at choice), F (saline, diets at choice). The stress treatment and food intake data record was the same as in experiment 1. At the day of 10, blood and hypothalamus were obtained. The results show that, stress reduced the production performance of broilers significantly, while high energy diet blunted the effect of stress on food intake; stress and diet energy level have no significant effect on glucose content of hypothalamus; changes of appetite regulated genes'mRNA level in hypothalamus suggested that in the state of chronic stress, broiler can maintain the balance of food intake regulation in hypothalamus via the controll of the energy intake. In experiment 3, there were two similar trails. In trial 1, 80 AA broilers were divided into two groups: stress and contro group. There were 10 repetitions in every group with 4 broilers in every repetition. From 11 days old to 13 days old, broilers were injected with the same dose of DEX and saline in experiment 1 at 6:00 (fasting for 3h), respectively. At the day of 13, samples (blood and hypothalamus) were obtained at 8:00 (stress for 2h, fasting for 5h) and 9:00 (stress for 3h, refeed for 1h). In trial 2, group dividing and the treatment were the same as which in trail 1, except that the time of injection was 10:00 (fasting for 1h), and samples were obtained at 12:00 (stress for 2h, fasting for 3h). The results primarily showed that, in the state of fasting, stress up-regulated the expressions of NPY and AgRP in hypothalamus significantly, while refeed vanished the effect.In part 2, trail 1, 32 chickens of 10-day-old was divided into 4 groups randomly, DEX (2.6mg/kg BW) and tryptophan (0.5g/kg BW) were adminstrated after 3h fasting at 9:00, and saline control was set up respectively. Blood and hypothalamus was obtained and hypothalamus extraction was used for NMR study. The ~1H NMR spectra shows that, the relative concentration of lactate, glucose, ATP, myo-Inositol and 3-Hydroxybutyrate was changed by stress, while tryptophan signal was unchangeable. In experiment 2, 32 AA broilers were divided into 4 groups. Broilers were fasted at 6:30, and 3 hours later, two groups were injected DEX and refeeded high energy diet. Another two groups were injected saline, and refeeded low energy level. At 11:30, all the blood samples were obtained, and hypothalamus were quick-freezed in liquid nitrogen. The results showed that, the detection of food intake regulated genes in hypothalamus showed primarly that, acute stress possibly induced the temporary increase of food intake via up regulated the expression of hypothalamic NPY.