Effect Of High Temperature And Dietary Crude Protein Level On Nitrogen Metabolism And Harmful Gases Generation In Broilers

(Objective) The aim of this research was to investigate the effects of high temperature anddietary crude protein level on parameters including growth and carcass trait, nitrogenmetabolism, nitrogen emission, harmful gases generation and some biochemical parameters inbroilers grown from28to42days of age.（Method）576Arbor Acres broilers were recruitedand2factors of3levels were used: factor1was the feeding mode, which contained23℃adlibtum （AL）,23℃fair-fed（PF） and28/32℃ad libtum（AL）; factor2was the dietary crudeprotein level, which was21.19%,18.18%,14.90%respectively. Nine treatments, each consistedof8repeats, were set, and each repeat contained8broilers. The trial period was lasted for14days.（Result）（1） During28to42days, the BW, ADG and ADFI of broilers in28/32℃ALseries were significantly lower than in23℃AL （P<0.01）, but not significantly different from23℃PF （P>0.05）. When exposed to high temperature, the carcass performance doesn’tsignificantly changed （P>0.05）, but the duodenum length and weight exponent weresignificantly decreased （P<0.01） in broilers of35days of age.（2） Under cycling hightemperature,adding synthetic EAA when the dietary crude protein was reduced from21.19%to14.90%can significantly（P<0.01） increased the semi-eviscerated carcass rate, evisceratedcarcass rate, abdominal fat rate and stomachus muscularis exponent, but other organ exponent,digestive organ exponent and BW, ADG, ADFI were not affected（P>0.05）.（3） The RT, RR ofbroilers were significantly increased （P<0.01） under cycling high temperature. There was aninteraction between high temperature and dietary CP levels in the respiratory rate, for comparedwith high dietary CP level, RR of broiler which under32℃and14.90%CP was significantlyincreased （P<0.05）.（4） Cycling high temperature doesn’t affects nitrogen body content,nitrogen deposition rate, and energy deposition rate （P>0.05）, but significantly decreasedaverage daily body amount of nitrogen deposition and energy deposition （P<0.05）.（5） Addingsynthetic EAA when the dietary crude protein was reduced from21.19%to14.90%, nitrogenbody content was significantly decreased （P<0.01）, nitrogen deposition rate （P<0.01）, averagedaily body amount of nitrogen deposition （P<0.01） and energy deposition rate （P<0.05） weresignificantly increased, but average daily body amount of energy deposition were invariant（P>0.05） under cycling high temperature.（6） Under cycling high temperature, nitrogenutilization and phosphorus utilization were significantly decreased （P<0.03）, nitrogen andphosphorus excretion per feed intake were significantly increased （P<0.03）. Nitrogen andphosphorus excretion per daily gain were significantly increased （P<0.01） on35days of age,but invariant （P>0.05） on42days of age.（7） Adding synthetic EAA when the dietary crudeprotein was reduced from21.19%to14.90%, nitrogen utilization, phosphorus utilization,phosphorus excretion per daily gain and phosphorus excretion per feed intake were invariant（P>0.05）, but nitrogen excretion per daily gain and nitrogen excretion per feed intake were significantly decreased （P<0.01） under cycling high temperature.（8） Under cycling hightemperature, NH₃, H₂S generation of cecum contents were significantly increased （P<0.05） in35day-old broiler, but they were not significantly increased （P>0.05） in42day-old broiler.（9）Adding synthetic EAA when the dietary crude protein was reduced from21.19%to14.90%,NH₃, H₂S generation of cecum contents were significantly decreased （P<0.05）, but H₂Sgeneration on42day-old was not significantly （P>0.05）.（10） For performance, nitrogenmetabolism, nitrogen emission and harmful gases generation, there were no interactionbetween high temperature and dietary CP levels.（Conclusion）Integrated all above, followingconclusions can be drawn:（1） Under cycling high temperature conditions, the growth of broilerwould slow down, the body nitrogen and energy deposition would reduce, the nitrogen andphosphorus emissions would increase, and the cecal NH₃and H₂S generation would increase.（2） Under cycling high temperature conditions, reducing dietary CP levels to14.90%by addingcomplementary synthetic EAA does not affect broiler growth rate, chest, leg muscle rate; butalter body composition, as t abdominal fat increased and nitrogen content decreased; whilenitrogen deposition increased, nitrogen emissions and cecal NH₃, H₂S generation decreased.（3）In terms of production performance, nitrogen metabolism, harmful gases generation, there wasno interaction between the cycling high temperature and dietary CP level.