| The negative effects of High environmental temperatures on growth and production performance of poultry have been investigated.Growth rate was decreased in broilers,when Suffering high environmental temperature,and feed intake,body weight,egg production,egg weight,and egg quality were all decreased in laying hens under high ambient temperature.However,this negative effects of heat stress on growth rate and production was not all due to the reduced of feed intake,production performance still significantly reduced under high environment temperature under the same feed intake,which indicated that the digestive function of chickens may be affect by high ambient temperature.However,with popularity of wet curtain and fans cooling system in recent years,the temperature in hen house can generally be controlled below30oC during summer days,and the negative effects of the high temperature was often ignored by most farmers,Whether the laying performance,egg quality and digestive function can be affect by this lower circulating temperature waere not clear.High environment temperature reduced feed intaked and Nutrients digestibility,further resulting in lack of nutrients and energy intake,which may be a main reason for the deleterious effects of high temperature on formance of laying hens.Therefore,whether can reduce the negative effect of high temperature on formance of laying hens by improve the nutritional levels needs a futher study.Experiment 1: 288 Hy-line Brown hens,28 wk of age,were randomly divided into four groups and housed in four controlled environment chambers.Four groups were 21°C normal thermal group,27~30°C cyclic temperature group,29~35°C cyclic temperature group and 21°C pair-feeding group(PF,pair-feeding on the daily feed consumption of high cyclic temperature group chickens)respectively.The experiment lasted for four weeks.Experiment 2: 288 Hy-line Brown hens,38 wk of age,were randomly divided into four groups and housed in controlled environment chambers.Four groups were I Low Energy(LE:ME2700 kcal/kg,CP16%),II Middle Energy(ME: ME2800 kcal/kg,CP16%),III High Energy(ME2900 kcal/kg,CP16%),IV High Crude Protein(ME2700 kcal/kg,CP18%).The experiment lasted for four weeks.The experiment conclusions were as follows.(1)Compared with 21°C group,the feed intake,body weight,egg weight,egg shell strength and yolk color were significant decreased(P<0.05)in 27~30°C group,while feed intake,body weight,egg weight,egg shell strength,egg shell thickness,albumen height and yolk color were all significant decreased(P<0.05)in 29~35°C group.Compared with PF group(under the same feed intake),the egg weight and shell strength were also significant decreased in 29~35°C group(P<0.05),and Feed/egg ratio was significant increased in 29~35°C group(P<0.05),while the egg quality in 29~35°C group was not affected(P>0.1).(2)Compared with 21°C group,no significant differences were found of Core body temperature(Tc)in 27~30°C group,and have no influence on MDA and antioxidant enzyme activity in serum and liver except the T-AOC concentration,which was significantly decreased in serum(P<0.05),and Ig A and Ig M concentration in serum were also foud significantly decreased in LCT group(P<0.05).While compared with 21°C group,the 29~35°C group significantly increased Tc and MDA concentration(P<0.05)and decreased T-AOC concentration in serum and liver(P<0.05),the GSH-Px activity in serum also has a tendency to decline(0.05<P<0.1),Ig A,Ig M and spleen index were all significantly decreased in 29~35°C group(P<0.05).Compared with the PF group,Tc of HCT group wassignificant increased(P<0.05),MDA concentration was significantly increased and T-AOC concentration was significantly decreasedin serum and liver(P<0.05),GSH-Px activity in serum was also significantly decreased(P<0.05).Compared with the PF group,only Ig A concentration in serum of 29~35°C group was significantly decreased(P<0.05).(3)Compared with 21°C group,in no significant differences were found of Nutrients digestibility were found in 27~30°C group(P>0.1).Digestive enzyme activity and its m RNA levels were also have no significant differences,except amylase in Jejunum and ileum was significant decreased(P<0.05).While in 29~35°C group,the protein metabolic rate has a tendency to decline(P<0.1)Compared with the 21°C group.There was no significant difference in digestibility of other nutrients(P>0.1).Amylase activity was significantly decreased(P<0.05),Jejunum amylase has a tendency to decrease(P<0.1).There were no significant differences in the activities of amylase,lipase,chymotrypsin and trypsin between the other intestinal groups and the control group(P>0.1).Pancreatic trypsin activity has a tendency to decrease(P<0.1),and Amylase,lipase and chymotrypsin were not significantly different(P>0.1),however there was no significant difference in the relative expression of digestive enzyme mRNA(P>0.1).In addition,the depth of jejunum crypt was significantly increased(P<0.05),and Villus height and crypt depth ratio decreased(P<0.1).Compared with the pair feeding group(under the same conditions of feed intake),the metabolic rate of protein has a tendency to decrease(P<0.1),fat and protein metabolic rate was significantly decreased(P<0.05),dry matter metabolic rate and AME value has a tendency to decrease(P<0.1).Ileum amylase activity was significantly decreased(P<0.05),Jejunum trypsin activity was significantly decreased(P<0.05).The activity of amylase in jejunum has a tendency to decrease(P<0.1).Pancreatic chymotrypsin was not significantly different(P>0.1),amylase and trypsin activity were significantly decreased(P<0.05).Lipase activity has a tendency to decrease(P<0.1).There was no significant difference in the relative expression of digestive enzymes(P>0.1).And There was also has no significant difference in the villus height,crypt depth and the ratio of the intestinal villi(P>0.1).(4)Improve dietary energy levels,there was a decreasing trend in feed intake(P<0.1),the feed intake of middle and high energy groups were significantly lower than that of low energygroup.Improve dietary energy levels,egg production rate and egg weight increased slightly(5.5%,0.8%),but did not reach a significant level,while the egg and egg ratio decreased significantly.Increase dietary protein levels,feed intake was significantly decreased(P<0.05),egg production and egg weight increased slightly(3.3%,1.2%),(P<0.05),but the ratio of egg to egg was significantly decreased(P<0.05).Increasing dietary energy and protein levels had no significant effect on egg shell and egg quality(P>0.1).In Conclusion,the results of present study demonstrated that production performance of laying hens were significant decreased even under 27~30°C.The effect of high temperature on laying performance and egg quality of laying hens was related to the decrease of feed intake,and the high temperature directly affected the formation of eggshell.The effect of cyclic temperature on antioxidant capacity and immune function may be associated with the rise of body temperature and the reduce of feed consumption respectively.The effect of high temperature on the performance of laying hens was not only related to the decrease of feed intake,but also has a direct effect on the digestive function of laying hens.Increasing dietary energy and protein levels significantly reduced feed intake,But the increase in energy and protein intake,increased use of diets,egg production and egg weight increase,while did not reach a significant level. |
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