| Yeast culture（YC）,as a non-polluting,residue-free and healthy micro-ecological preparation,has been widely used as a nutrient regulator for ruminants.YC can improve animal production performance and product quality by regulating rumen bacterial community composition（BCC）and rumen metabolism,and increasing nutrient digestibility.There was a significant difference in YC utilization,and the diet composition is the one of important factors affecting the effective of YC.Based on 16S rDNA high-throughput sequencing technology,metabolomics technology,multivariate statistical analysis and other research methods,this study carried out a series of research on the effect of YC supplementation under different energy structure diet conditions.The purpose of this study was to evaluate the effects of YC supplementation on the rumen fermentation,nutrients digestion and metabolism,and fattening performance in sheep under different energy structure diet conditions,to investigate the mechanism of yeast culture,and provide theoretical basis for effective utilization of yeast culture in ruminant nutrition.Experiment 1:Effects of YC supplementation and dietary energy structure on rumen fermentation parameters（RFPs）,ruminal BCC and metabolome in sheepThis study aimed to evaluate the effects of YC supplementation and dietary non-structure carbohydrate/fat ratio（NSCFR）on RFPs and BCC using 6 ruminally cannulated sheep（age 12±1 month;body weight 30.5±2.13 kg）in a 2×3 factorial experiment.We formulated 6 dietary treatments with 3 levels of YC supplementation（0,0.8 and 2.3 g/kg of dietary dry matter）and 2dietary NSCFRs（17.02 and 5.60）.Each animal was fed 1 of 6 diets in a 6×6 Latin square arrangement during the experiment.Ruminal liquid was sampled at 0,2,4,6,8,and 12 hours after morning feeding on days 16 and 17（last 2 days）in all 6 of the Latin square periods.The results of RFPs showed that every indices were changes obviously at 2 hours after feeding.Supplementation of YC significantly increased the concentrations of acetic acid,butyric acid,TVFA and the ratio of acetic to propionic acid ratio（A/P,p<0.05）,and decreased the concentration of NH3-N（p<0.05）.Affected by dietary energy structure,the ratio of NH3-N,butyric acid,TVFA and A/P in H groups was significantly higher than that in L groups（p<0.05）,while pH and acetic acid concentration were significantly lower than that in L groups（p<0.05）.Moreover,all the RFPs were affected by the interaction between YC and NSCFR at 2hours after feeding except A/P（p<0.05）.Supplemental YC in H diet significantly decreased the pH values at 2 hours,while that in L groups with 0.8 g/kg of YC have a increased tendency of pH values（p=0.067）.With time progressing,the NH3-N concentration was increased followed by a decrease with YC supplementation,whereas there were lower（p<0.05）in L diet with YC supplementation than that without YC in every period after feeding.Supplementation of YC in H diet resulted in a significant increase in the concentrations of acetic acid,butyric acid and TVFA（p<0.05）,while the difference was not significant in L diet.Ruminal BCC was significantly affected by dietary NSCFR,YC and the YC×dietary NSCFR interaction.Supplementation of YC in both diets increased the relative abundance of Prevotella1,but increased more in the L group.Supplemental 2.3 g/kg of YC in H groups significantly increased the relative abundances of Ruminococcus2,RuminococcaceaeUCG-014,CandidatusSaccharimonas and[Ruminococcus]gauvreauii（p<0.05）,but the difference was not significant or opposite in L groups.Supplementation of 0.8g/kg of YC in L diet significantly increased the relative abundances of Pseudobutyrivibrio,Saccharofermentans,RikenellaceaeRC9 and Butyrivibrio2（p<0.05）,while the difference was not significant or opposite in H groups.The results of metabolome showed that YC supplementation significantly regulated the starch and sucrose metabolism,valine,leucine and isoleucine degratation and synthesis,unsaturated fatty acid synthesis,carbohydrate digestion and absorption,fructose and mannose metabolism in both diet groups（p<0.05）.Supplementation of YC in H diet significantly regulated steroid metabolism,fat digestion and absorption,fatty acid elongation,fatty acid degradation,and fatty acid metabolism（p<0.05）,whereas in the L group,protein digestion and absorption,phenylalanine acid metabolism and amino sugar and ribose metabolism were significantly affected by YC supplementation（p<0.05）.Experiment 2:Effects of YC supplementation and dietary energy structure on nutrient digestiblity,growth performance,carcass quality and longissimus dorsi muscle fatty acid profile in sheepThe aim of this study was to evaluate the effects of different energy diets supplemented with YC on nutrient digestibility,growth performance,carcass quality and LD muscle fatty acid profile.Thirty-six male small-tailed Han sheep（87±2.5 days old,body weight 23.93±1.86kg）were selected as experimental animals,and a 2×3 factorial test design was used.According to the NRC（2012）,two total mixed pellet rations with a similar proportion of NSCFR as experiment one were constructed,which were high-starch（H,11.37）and high-fat（L,4.57）,respectively.There were 6 treatment groups in the trial:H diet without YC（Hc）,H diet supplemented with low level YC（0.8g/kg,Hl）,H diet supplemented with high level YC（2.3g/kg,Hh）,L diet without YC（Lc）,L diet supplemented with low level of YC（0.8 g/kg,Ll）and L diet supplemented with high level of YC（2.3 g/kg,Lh）.The trial included a 15-day pre-feeding period and a 60-day feeding period.The whole fecal and urine collection method was used for digestion and metabolism test on the 55th to 59th days All the sheep were slaughtered on the 61st day.During the feeding period,the average daily gain（ADG）,dry matter intake（DMI）,and diet conversion ratio（FCR）for each sheep were recorded and calculated.The body weight（DW）,slaughter rate（DP）,backfat thickness（BFT）,visceral fat weight（VFW）,internal fat percentage（VFR）and fur weight（SWT）of all the experimental animals were obtained after slaughtering.The LD muscle samples used for the determination of nutrients and fatty acids.The results showed that YC supplementation in H diet significantly increased the CP digestibility and metabolic rate（p<0.05）,and supplemental high dose of YC increased NDF digestibility（p=0.12）,reduced the BUN concentration（p<0.05）,but no significant difference were observed in above mentioned 5 indices of L group.The TCHO concentrations in the Hl,Hh and Lh groups were lowered（p<0.05）,while the GLU concentrations was increased（p<0.05）,compared with their control groups respectively.High-dose of YC supplementation in L diet significantly reduced BHBA concentrations,but had no significant effect on H diet（p<0.05）.Supplementation of high-dose YC in H diet more effective increased the ADG and GR in sheep（21 g/d,5.8%）,while the supplementation of low-dose YC in L diet was the most effective（32g/d,8.7%）.Supplementation with high-dose YC significantly increased visceral fat weight（VFW）and visceral fat ratio（VFR）in both two feed treatment groups（p<0.05）.H diet supplemented with both doses of YC significantly reduced the contents of crude fat and saturated fatty acids（SFA）in the LD muscle（p<0.05）,and high dose of YC significantly increased polyunsaturated fatty acids（PUFA）content（p<0.05）.Supplementation of low-dose YC in L diet significantly increased LD crude fat content（p<0.05）and decreased monounsaturated fatty acid（MUFA）content（p<0.05）.Based on the results of this study,the dietary energy structure and YC supplementation level had significant effects on the RFPs,ruminal BCC,nutrients digestion and metabolism,the fattening performance and carcass quality.Moreover,there are significant interaction effects between dietary energy structure and YC supplementation level on many indicators of rumen function and environment,nutrient digestion and metabolism and fattening performance.Supplemental high-dose YC in high-starch diet can significantly increase VFA production,improve rumen BCC,regulate metabolic pathways,increase nutrient digestibility and growth performance,and increase PUFA content in the LD muscle.However,these indicators have shown opposite trends in high-fat diets.On some important indicators,the optimal result appeared in the low-dose YC group.These findings demonstrate that the use of YC in the fattening process of sheep should determine the amount of additive as appropriate,depending on the composition of the energy structure of the diet. |
