| Feeding behavior is the primary route for animals to obtain nutrients from the environment,and it is also one of the most important basic activities for survived.Feed intake is closely related to the growth and production performance of poultry,and is the basis for assessing energy metabolism and nutritional requirements of poultry.In modern intensive chicken production system,the feeding behavior of poultry is regulated by environment,feeding management,metabolites,central and peripheral signal factors.This study focused on the rhythm of feeding behavior of laying hens and the effects of environmental temperature,lighting regime and feeding frequency on the feeding behavior of laying hens,providing the mechanisms of its regulation.Trial 1: Effects of intermittent different temperature on feeding and intestinal development of growing layersIn this experiment,11-week-old Isa Brown layers with similar body weights were divided into five treatment groups.The light time was maintained for 8 hours per day(9:00h-17:00h).The control temperature was maintained at 22?,while four temperature treatments of 24?,26?,28?,and 30? were applied respectively.Temperature treatments were operated for 8 hours at 10:00h-18:00h per day,and rested at base temperature of 22?.Results showed that feed intake at 22? was higher than at 28? group at the first 6 weeks of heat treatment(P<0.05).Feed intake was higher at 24? group and lower at 30? group during the last two weeks of heat treatment(P<0.05).During the non-heat-treatment period,feed intake of the 30? group was still the lowest,and the average hourly feed intake of the non-heat-treatment period was higher than that of the heat treatment period(P<0.05).After 4 weeks of intermittent heat treatment,the intestinal tract index showed a significant increase at 26? and 28? group(P<0.05).In the latter period,the index of intestinal tract showed significant decrease at 22? group;Index of Jejunal showed a significantly decrease in the 30? group(P<0.05).At the latter period of the experiment,hypothalamic NPY(Neuropeptide Y)expression was significantly increased at 24? group(P<0.05).The expression of POMC(Pro-opiomelanocortin)in hypothalamus and CCK(Cholecystokinin)in duodenum were significantly increased with high temperature treatment,whereas expression of ghrelin in the proventriculus was significantly increased at low temperature treatment(P<0.05).Trial 2: A study on the feeding peak and its mechanism in laying hens before light-offIn this experiment,70-week-old Hy-line Brown laying hens with similar body weights and egg production were used.The hens were randomly subjected to two treatments:(1)Treatment groups(light from 2:00h to 18:00h);(2)Control groups(light from 5:00h to 21:00h).And the experiment last 4weeks.The results showed that the feeding peak appeared at 3 hours before lights off(P<0.05).With the advance of light phase,the timing of feeding peak also moved forward.The expression of anorexigenic neuropeptide was significantly lower at feeding peak,while clock genes such as Per2(Period 2)and Cry1(Cryptochrome 1)had higher expression at the time of feeding peak,with Cry1 having lower expression at the end of feeding peak(P<0.05).There was no significant difference about the clock genes of the proventriculus.Trial 3: Effects of different lighting regime during growing period on feeding and intestinal development of laying hensIn this experiment,11-week-old Isa brown layers with similar body weights were random divided into three groups: the light time in treatment 1 reduced by 1 h per week until 8 h finally(T1),light time in treatment 2 reduced 2 h per week until reaching 8 h finally(T2);while light time in the control group was reduced from 14 h to 8 h directly.The results showed that the feed intake in treatment 1 and treatment 2 had a significantly increase compared with the control group(P<0.05).The length of duodenum and ileum significantly increased in treatment 2 whereas the length of ileum increased significantly in the treatment 1(P<0.05).Reducing lighting at 2 h per week significantly increased the index of ileum and jejunal(P<0.05).The expression of NPY in hypothalamus was significantly increased by declining lighting by 2 h every week during the growing period(P<0.05).Trial 4: Effects of different feeding frequency on feed intake and intestinal development of laying hens.In this experiment,10-week-old Hy-line brown laying hens with similar body weights were selected and randomly divided into the control group and two treatment groups.The control group was fed once a day at 9:00h,with a feeding weight of 150 g per hen.Treatment one had two feeding times at 9:00 and 13:00,with a feeding weight of 75 g per hen at each time.Treatment two was four feeding times at 9:00,11:00,13:00 and 15:00,with a feeding weight of 37.5 g per hen at each time.The results showed that increased feeding frequency reduced feed intake(P<0.05).Body weight was significantly decreased in the multiple feeding groups(P<0.05).Four feeding times per day significantly reduced liver index and ileum length,and four feeding times per day significantly increased proventriculus index(P<0.05).Four feeding times per day significantly increased plasma glucose level and inhibited feeding of laying hens(P<0.05).The level of plasma triglyceride was significantly increased after feeding(P<0.05).And mRNA expression of POMC in hypothalamus and Ghrelin expression in proventriculus were significantly increased after feeding(P<0.05),which subsequently inhibited feeding behavior.This may account for decline in feed intake with increasing feeding frequency.Conclusively,the study showed that maintaining the ambient temperature at 24? during the growing period is conducive for the growth and development of laying hens.High temperature treatment could reduce feed intake and cause intestinal damage.High temperature group can also stimulate the mRNA expression level of POMC in hypothalamus and CCK in duodenum,thus inhibiting feed intake of laying hens.The feeding peak appeared before the subjective dusk,and the circadian rhythm system played a key role in the emergence of the feeding peak.Reducing illumination time during the growing period can stimulate the expression of POMC in hypothalamus to promote feeding.Also,increasing the feeding frequency can increase plasma glucose concentration and inhibit feeding of laying hens. |
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