| The rumen is a special digestive organ of ruminants,and its developmental state directly affects the performance and health of ruminants.In young ruminants,the rumen is not fully developed and it is unprepared for the digestion and absorption of solid feed.Promoting the rumen development in early life will help facilitate early weaning,reduce weaning stress,and allow for optimal performance.Therefore,accelerating the rumen development and maturation during early life through nutritional strategies may have great potential for long-term animal performance and health in ruminants.1.Effect of oral infusion of sodium butyrate on performance,blood parameters,rumen fermentation and epithelial morphology in lambsSeven pairs of newborn twin Hu lambs were chosen and assigned randomly.At 10 days old,one lamb received oral infusion of sodium butyrate(SB)at 1.8 ml/kg body weight(0.36 g/kg BW)(SB,n=7),while the other lamb was given the same volume of saline(Con,n=7)once a day,the amount of infusion was adjusted weekly according to BW.The starter,alfalfa and oat grass were fed ad libitum during the experimental period.All lambs had free access to water.The starter intake of lambs was recorded every day.The body weight of lambs was measured weekly before the morning feeding.At 49 d of age,all lambs were slaughtered after last infusion SB for 2 h.Results showed that the average daily feed intake(ADFI)of starter(P=0.010),average daily gain(ADG)(P=0.022),BW of lambs at ages of 5 weeks(P=0.028)and 6 weeks(P=0.032)in SB group were greater than those in Con group,while there were not significantly different(P>0.05)in BW of lambs at ages of 2 weeks,3 weeks,4 weeks and 7 weeks.The concentration of BHBA(P=0.009)and IGF-1(P=0.010)in blood plasma were greater in the SB group than those in the Con group,whereas there was not significantly different in the plasma glucose concentrate(P=0.524).Compared with Con group,infusion of SB significantly improved the concentration of total volatile fatty acids(P=0.020),acetate(P=0.048)and butyrate(P=0.002),as well as butyrate proportion(P=0.001),however,the proportion of other VFA proportion(P=0.033)was significantly reduced in rumen.SB infusion promoted rumen papillae growth,depicted by higher rumen dry weight(P=0.043),larger rumen papillae length(P=0.017),width(P=0.004),and surface area(P=0.002),greater thickness of stratum corneum(P=0.017),and total epithelium(P=0.048).Correlation analysis showed that there was significant positive correlation between the concentration of butyrate in the rumen fluid and the length(P<0.001;r=0.81)and surface area(P<0.001;r=0.79)of the rumen papillae.These results indicated that oral infusion of sodium butyrate improved the growth performance,promoted the rumen fermentation process and the morphological development of rumen papillae in suckling lambs.2.Effect of oral infusion of sodium butyrate on rumen epithelial proliferation and VFA absorption and metabolism in lambsAt 49 d of age,all lambs were slaughtered after last infusion SB for 2 h.Results showed that SB supplementation up-regulated the mRNA expression of Cyclin A2(P=0.043),Cyclin D1(P=0.047)and CDK6(P=0.004),and down-regulated the mRNA expression of Caspase-3(P=0.047)and Bax(P=0.020)in the rumen epithelium.Compared with the Con group,SB group up-regulated the mRNA expression of IGF-1R(P=0.031)and IGFBP-5(P=0.015),and down-regulated the mRNA expression of IGFBP-3(P=0.023)in the rumen epithelium of lambs.Meanwhile,SB infusion up-regulated the mRNA expression of MCT1(P=0.042),DRA(P=0.019),HMGCS2(P=0.005),and HMGCL(P=0.015)in the rumen epithelium,while down-regulated the mRNA expression of NHE2(P=0.024).Correlation analysis showed that the concentration of butyrate in rumen fluid was positive correlated with plasma IGF-1 concentration(P=0.007;r=0.68),IGF-1(P=0.026;r=0.59)and 1GF-1R(P=0.040;r=0.55)mRNA expression in rumen epithelium,and negative correlated with IGFBP-3(P=0.015;r=-0.63)and Caspase-3(P=0.014;r=-0.64)mRNA expression in rumen epithelium.There was significant positive correlation between plasma IGF-1 concentration and Cyclin A2(P=0.036;r=0.56)mRNA expression,and significant negative correlation with Caspase-3(P=0.041;r=-0.55)mRNA expression.In summary,oral infusion of sodium butyrate promoted the rumen papillae growth related to cell proliferation accelerated and cell apoptosis inhibited,and enhance expression of genes involved in rumen epithelial VFA uptake and metabolism in pre-weaning lambs.The underlying mechanism of sodium butyrate promoting rumen epithelial growth is closely related to IGF-1 pathway in suckling lambs.3.The underlying mechanism of sodium butyrate promote rumen epithelial proliferation was based on IGF-1 signaling pathway in suckling lambsThe primary rumen epithelial cells were isolated with trypsin digestion from four 49-day lambs.After the cells adhered to the wall,they were divided into following groups:Control group(Con,n=4),2 mM sodium butyrate group(2 mM SB,n=4),4 mM sodium butyrate group(4 mM SB,n=4),8 mM sodium butyrate group(8 mM SB,n=4),sodium butyrate+IGF-1R inhibitor group(SB+PPP,n=4).The trials were repeated 4 times.The same volume of DMEM was added to the Con group.When the cells were treated for 24 h,the cell fluid was collected for determinate IGF-1 concentration,and the cells were collected to analyses the expression of genes related to cell cycle and proliferation and apoptosis.Results showed that the proportion of cells in G0/G1 phase(P<0.001)and S phase(P<0.001)of rumen epithelial cells were changed quadratically with the increase of sodium butyrate concentration,the proportion of G0/G1 phase cells in the 0 mM and 8 mM sodium butyrate group was significantly higher than that in the 2 mM and 4 mM sodium butyrate group,and the proportion of G0/G1 phase cells in the 8 mM sodium butyrate group was significantly higher than that in 0 mM sodium butyrate group,the proportion of G0/G1 phase cells in the 2 mM sodium butyrate group was significantly higher than that in 4 mM sodium butyrate group.The proportion of S phase cells in the 4 mM sodium butyrate group was significantly higher than that in the 0 mM,2 mM and 8 mM sodium butyrate group,and the proportion of S phase cells in the 8 mM sodium butyrate group was significantly lower than that in the 2 mM sodium butyrate group.The proportion of cells in the G2/M(P=0.007)phase was decreased linearly with the increase of sodium butyrate concentration,and the proportion of cells in the G2/M in the 8 mM sodium butyrate group was significantly lower than that in the 0 mM,2 mM and 4 mM sodium butyrate group.The mRNA expression of Cyclin A2(P=0.006)and CDK1(P=0.007)in the rumen epithelial cells of lambs was decreased linearly with the increase of sodium butyrate concentration,the expression of Cyclin A2 in the 8 mM sodium butyrate group was significantly lower than that in the 0 mM,2 mM and 4 mM sodium butyrate group,and the CDK1 expression in the 8 mM sodium butyrate group was significantly lower than that in the 0 mM and 2 mM sodium butyrate group.The mRNA expression levels of Cyclin D1(P<0.001),CDK4(P=0.034)and CDK6(P=0.003)in the rumen epithelial cells of the lambs was changed quadratically with the increase of sodium butyrate concentration,the expression of Cyclin D1 in the 2 mM and 4 mM sodium butyrate groups was significantly higher than that in the 0 mM and 8 mM sodium butyrate group,and the in the 8 mM sodium butyrate group was significantly lower than that in the 0 mM sodium butyrate group.The expression of CDK4 in the 4 mM sodium butyrate group was significantly higher than that in the 0 mM,2 mM and 4 mM sodium butyrate groups.The CDK6 expression in the 2 mM and 4 mM sodium butyrate groups was significantly higher than that in the 8 mM sodium butyrate group.The mRNA expression of Caspase-3(P=0.039)and Bax(P=0.008)in the rumen epithelial cells of lambs were increased linearly with the increase of sodium butyrate concentration,and it was significantly higher in the 8 mM sodium butyrate group than that in 0 mM,2 mM and 4 mM sodium butyrate group.Before SB addition,the SB+PPP group was treated with 2.5μM IGF-1R inhibitor(PPP)to block the IGF-1 signal pathway.After adding SB for 24 h,the cells were collected for analysis of gene related to proliferation and apoptosis,and the cell culture fluid was collected for determination of IGF-1 concentration.Results showed that IGF-1 concentration(P=0.014)in cell culture fluid and IGF-1 R(P=0.028)mRNA expression of rumen epithelial cell in the SB+PPP group were significantly lower than those in the 4 mM SB group.In addition,the mRNA expression of Cyclin D1(P=0.042)and CDK4(P=0.028)in SB+PPP group was significantly lower than that in 4 mM SB group(P<0.05).These results suggested that 4 mM SB significantly promoted the rumen epithelial cell proliferation,mainly through the IGF-1 signaling pathway in suckling lambs. |
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