Effects Of Environmental Temperature And Dietary Energy Composition On Energy Metabolism And CO₂ Emission In Growing Pigs

Environmental temperature and dietary energy composition have been considered as influential factors for energy metabolism and distribution in growing pigs.Low temperature leads to stimulate the body's energy metabolism and to change the nutrient utilization of fat,carbohydrate and protein,leading to the change in energy deposition.Thus,exploring a suitable feed composition during exposure to low environmental temperature has a great impact on energy metabolism.Such exploring provides references for low carbon industry.Although the dietary energy values and crude protein content are described when pigs live in comfortable environment in feeding standards,the composition and proportion of energy material have not been demonstrated.Moreover,the proportion of dietary energy on the energy metabolism of growing pigs remains to be further research,in order to improve the energy material utilization under low environmental temperature.Therefore,this study aims to evaluate the effects of temperature and dietary energy composition on growth performance,nutrient oxidation and energy metabolism in growing pigs,as well as to elucidate the change in gene expression of lipid metabolic pathways on the molecular level.Thus,the current study can provide theoretical basis for optimization of energy structure and regulation of CO₂ emission in pigs,under low environmental temperature.This research mainly includes the following content: Experiment 1: Effects of environmental temperature and dietary energy composition on growth performance and nutrient digestibilityThirty-two pigs?Duroc×Landrace×Large White?with initial weight of 25.16±1.91 kg were assigned to treatments in 2×4 factorial design.All pigs were divided into eight treatments and each treatment consisted of 4 replicate.All pigs were fed with two isoenergetic and isoproteic diets of different fat levels?fat level: 0 and 5% fat?under four environmental temperatures?23 oC,18 oC,13 oC or 8 oC?.After 21 days feeding,growth performance and nutrient digestibility reflected the interaction effect of environmental temperature and energy composition on growth and digestion of the growing pigs.The results showed that:The results of the growth performance showed that the average daily feed intake?ADFI?was significantly increased with the temperature decreasing?P<0.001?.The average daily gain?ADG?was significantly reduced with the temperature decreasing?P<0.001?.F/G was significantly increased with the temperature decreasing?P<0.001?.Energy composition of dietary had no effect on ADFI,ADG and efficiency of feed utilization at all temperatures?P>0.05?.There was no interaction between temperature and energy composition on growth performance.The digestibility experiment results indicated that there was no effect of temperature and energy composition on apparent digestibility of energy?P>0.05?.The apparent digestibility of protein was significantly decreased with the temperature decreasing?P=0.007?.There was no significantly difference between two fat level dietary groups,the apparent digestibility of protein had a tendency to decrease in HF group?P=0.051?.The apparent digestibility of fat was significantly decreased with the temperature decreasing?P<0.001?,there were no obvious difference in two fat level dietary groups?P=0.616?.There was no interaction between temperature and energy composition on the apparent digestibility of energy and nutrients.Experiment 2: Effects of environmental temperature and dietary energy composition on CO₂ emission,nutrient oxidation and energy metabolismThe design of the experiment is the same as that of experiment one.This part aimed to evaluate the effect of temperature and dietary energy composition on CO₂ emission,heat production,nutrient oxidation and energy metabolism used gas exchange and carbon-nitrogen balance in growing pigs.The results showed that:The respiratory quotient?RQ?was decreased with the temperature decreasing,RQ of 18 oC and 23 oC group were greater than 1 with LF diet,RQ of 13 oC and 8 oC group were less than 1.In HF group,RQ was less than 1 in each temperature group.The CO₂ emission and O₂ consumption were significantly increased with the environmental temperature decreasing?P<0.001?.The CO₂ emission in HF was significantly lower than LF group?P=0.013?,O₂ consumption was significantly higher than LF group?P=0.038?.There was no interaction between temperature and energy composition on the CO₂ emissions and O₂ consumption.The results of energy metabolism showed that the energy intake,energy in urine and total heat production?HP?were significantly increased with the temperature decreasing?P<0.05?.Energy retention on 23 oC,18 oC and 13 oC group were not significant difference,but had a tendency to reduce with temperature decreasing,energy retention on 8 oC was significantly lower than the other groups?P=0.013?.The effect of dietary energy composition on each index of energy metabolism has not reached significant level?P>0.05?.There was no interaction between temperature and energy composition on each index of energy metabolism.Significant interactions between environmental temperatures and energy composition were observed on carbohydrate oxidation?OXCHO?and fat oxidation?OXF??P<0.001?.The OXCHO was significantly greater in the 8 oC group than the other groups?P<0.001?.OXCHO was significantly decreased in HF group?P<0.001?.The OXF was significantly increased with the temperature decreasing?P<0.001?,OXF was significantly increased in HF group?P<0.001?and amount of OXF increased by 306% than LF group.No significant differences were observed for protein oxidation?OXP?in different environmental temperatures and energy composition diets.HP contributed from OXCHO was significant decreased?P<0.001?,while that from OXF was significant increased?P<0.001?with environmental temperature decreasing.HP contributed from OXCHO was decreased?P<0.001?,but HP from OXF was increased?P<0.001?in high fat than in low fat groups.No differences in the ratio of OXP to HP were observed due to either dietary fat level or temperature.The daily nitrogen intake,nitrogen in feces?FN?and urine?UN?were significantly increased with the temperature decreasing?P<0.05?.Nitrogen digestibility ratio was significantly decreased with the temperature decreasing?P=0.003?.The temperature did not influence nitrogen retention ratio but there was a tendency?P=0.059?that N retention ratio will reduced with the temperature decreasing.There had no significant difference for nitrogen metabolism with different dietary energy composition?P>0.05?.No significant interaction was observed between temperature and energy composition of diets for nitrogen balance.The daily carbon intake,carbon in feces?FC?and urine?UC?and gaseous C losses were significantly increased with the temperature decreasing?P<0.05?.C retention was significantly decreased with the temperature decreasing?P=0.048?.The carbon intake,UC and C retention were not significantly affected by different dietary energy composition?P>0.05?.FC was significantly increased with HF diet?P=0.047?.Gaseous C losses was significantly decreased with HF diet?P=0.017?,amount of gaseous C losses decreased by 3% than LF group.No significant interaction was observed between temperature and energy composition of diets for carbon balance.Experiment 3: Effects of environmental temperature and dietary energy composition on blood parameters and lipid metabolism genes expression of liverThe design of the experiment was the same as that of experiment one.This part aimed to evaluate the effect of temperature and dietary energy composition on nutrient and energy metabolism by blood parameters and lipid metabolism genes expression of liver.The results showed that:In LF group,the TP and GLU were significantly lower than the other groups with the temperature decreasing?P<0.05?.UN was significantly increased with the temperature decreasing?P<0.05?.GLU was significantly increased and INS was significantly decreased with the temperature decreasing?P<0.05?.T4 was significantly increased with the temperature decreasing?P<0.05?.The trends of blood parameters in HF were similar to LF group.CPT-1 and PPAR? mRNA expression in liver were significantly increased with temperature decreasing?P<0.05?.CPT-1 and PPAR? mRNA expression were also affected by energy composition of diets,CPT-1 mRNA expression in HF group were significantly greater than LF groups under 23 oC and 13 oC?P<0.05?.PPAR? mRNA expression in HF group were significantly increased under 13 oC,18 oC and 23 oC?P<0.05?,there was no significant difference of PPAR? mRNA expression in HF and LF group under 8 oC?P>0.05?.These results indicated that growth performance,CO₂ emission,nutrition and energy metabolism,nutrient oxidation and contribution of nutrients to HP are influenced by the environmental temperatures in which they are maintained.The nutrition and energy deposition are not affected by energy structure adjustment,but contribution of nutrients to HP are changed,CO₂ emission is reduced.