| The purpose of this study was to investigate the effects of high temperature on growth performance,intestinal health and antioxidant status in weaned piglets and the significance parameters were selected as thermal indicators to explore the upper critical temperature.This work may provide a reference for the summer management of weaned piglets.Two experiments were included in this study:Exp.1 Effects of High Temperature on Growth Performance,Intestinal Health and Antioxidant Status in Weaned PigletsThe purpose of Exp.1 was to investigate the effects of high temperature on growth performance,intestinal health and antioxidant status in weaned piglets.A total of sixteen weaned piglets(Duroc × Landrace × Yorkshire,DLY)with an average initial body weight at 8.61 ± 0.24 kg(28 days of age)were randomly allotted into two groups(CON,HT)with8 replicates per group and 1 piglet per replicate.The room temperature among groups were controlled at 26±1℃ or 35±1℃.The trial lasted for 21 days.The results showed that:compared with CON group,1)Piglets in HT group has a higher temperature humidity index(THI)and increased rectal temperature(P<0.05);2)The ADFI and ADG of piglets in HT group were significantly decreased by 43.13%、50.36%(P<0.05),and F/G was significantly increased by 16.06%(P<0.05);3)There were no significant difference in the apparent digestibility of nutrients among groups(P>0.05);4)The organ indexs of liver,spleen and thymus of piglets in HT group were significantly decreased(P<0.05);5)The villous height(VH)of duodenum、jejunum and ileum of piglets in HT group were significantly decreased(P<0.05),the crypt depth(CD)of duodenum was significantly increased(P<0.05),the VH/CD of duodenum and ileum were significantly decreased(P<0.05);6)The MDA level of piglets in HT group was significantly increased(P<0.05),while the T-SOD activity was significantly decreased(P<0.05);7)The HK activity in semitendinosus muscle of piglets in HT group was significantly decreased(P<0.05),while the HK activity in longissimus dorsi muscle was decreased with a tendency(P=0.059);8)The observed-species index,PD whole tree index and Shannon index of piglets in HT group were significantly increased(P<0.05),indicating that there was significant difference in species richness and diversity between the two groups;at the genus level,the abundance of Desulfovibrio,Occillibater and Catenisphaera of colonic microbiota of piglets in HT groups were significantly increased(P<0.05),and heat stress significantly reduces the function of glycan biosynthesis and metabolism,transport and catabolism,lipid metabolism,metabolism of other amino acids,biosynthesis of other secondary metabolites,aging,endocrine system,signaling molecules and interaction of core flora of colon(P<0.05),but significantly increased the function of signal transduction,cell motility,transcription and genetic information processing(P<0.05).Therefore,high temperature leads to heat stress and oxidative stress of weaned piglets,which leads to decrease of growth performance,organ development inhibition,integrity of intestinal structure impair,and serum antioxidant function decreased,resulting in colonic microbe structure and function disorder.Changes in the function of gut microbial core flora may help host adapt to heat stress.Exp.2 Study on the upper critical temperature of weaned pigletsThe Exp.2 was to study on the upper critical temperature of weaned piglets with different thermal sensitive indexs.A total of thirty-two weaned piglets(DLY)with an average initial body weight of 7.25 ± 0.08 kg(21 days of age)were randomly allotted four groups(26℃ group,29℃ group,32℃ group and 35℃ group)with 8 replicates per group and 1 piglet per replicate.The trial lasted 21 days.The room temperature among groups were controlled at 26±1℃,29±1℃,32±1℃,35±1℃,all pigs fed basal diet.The trial lasted for 21 days.The results showed as follows: compared with 26℃ group,1)The rectal temperature of piglets in 29℃ group and 32 ℃ group were no significantly change(P>0.05),but piglets in 35℃ group was significantly increased(P<0.05);2)The ADFI and ADG of piglets in 29℃ group、32℃ group and 35℃ group was significantly decreased(P<0.05),piglets in 35℃ group was significantly increased the F/G(P<0.05),and according to regression equation of ADFI and ADG,the critical temperature were 30.02℃ and 30.63℃;3)There were no significant difference on the apparent digestibility of nutrients among groups(P>0.05);4)The organ index of liver,spleen,lung and thymus of piglets in 35℃ group was significantly reduced(P<0.05),and according to regression equation of spleen and thymus,the critical temperature were 35.12℃ and 34.83℃;5)The VH and VH/CD of the duodenum,jejunum and ileum of piglets in 29℃ group,32℃ group and 35℃ group were significantly decreased(P<0.05),the CD of the duodenum of piglets in 29℃ group,32℃ group and 35℃ group were significantly increased(P<0.05),and according to regression equation of intestinal morphology,the critical temperature were 30.12℃,30.16℃,29.88℃;6)The relative expression of ZO-1、ZO-2 and Occludin in jejunum mucosa of piglets in 29℃ group,32℃ group and 35℃ group were significantly decreased(P<0.05).Therefore,the upper critical temperature for significant change of ADFI and ADG were 30.0～30.6℃,the upper critical temperature for significant change of intestinal morphology were 29.9～30.2℃,the upper critical temperature for significant change in organ index of spleen and thymus were 34.8～35.2℃.In summary,under the condition of this experiment,high temperature induced heat stress and oxidative stress of weaned piglets,which leads to growth performance decrease,organ development inhibition,structure integrity and barrier of intestinal impairment,and colonic microbe structure and function disorder.The upper critical temperature for significant change of ADFI and ADG were 30.0～30.6℃,the upper critical temperature for significant change of intestinal morphology were 29.9～30.2℃,the upper critical temperature for significant change in organ index of spleen and thymus were 34.8～35.2℃. |
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