The Unaffected Rumen Fermentation Parameters By Lowering DCAD Establish Its Feasibility For Hypocalcemia Prevention Of Goats

Reducing dietary cation-anion difference（DCAD;mmol/kg DM）can improve the blood calcium level,and then prevent hypocalcemia.Rumen fermentation is an important research content for ruminant nutrition.Till now,there is insufficient information on the effect of lowering DCAD on rumen fermentation in goats,therefore,based on the previous achievements of our research group,the present study is conducted to evaluate the effect of reducing DCAD and negative DCAD plus Ca,Ca and Mg on rumen fermentation and microflora composition and abundance,and growth performance,humoral metabolism,blood gas and plasma biochemicals as well.The result would lay the basis for a comprehensive evaluation on the feasibility of reducing DCAD for goat production in the practice.The paper consists of 3experiments.Experiment 1:Effect of Lowering DCAD on growth performance,humoral metabolism,rumen fermentation parameters and microflora of goatsExperiment design:Eighteen goats were randomly allotted to 3 blocks of 6replications with 1 goat each.Animals were fed 1 of 3 diets with varying DCAD levels at+338（HD）,+152（CON）,and-181（LD）,respectively.The detected indicators included growth performance,urine pH,plasma Ca,Glu,UN,GPT,GOT,AKP,TP,Alb,GSH-Px,CAT,SOD,and MDA;rumen pH,VFA,cellulolytic bacteria;and microflora composition and abundance.Results:（1）Compared with HD and CON,LD had no effect（P>0.05）on growth performance.（2）Urine pH in LD was lower（P<0.05）than HD and CON.（3）Feeding of LD resulted in higher（P<0.05）plasma Ca over HD and CON;DCAD variation had no effect（P>0.05）on plasma Glu,UN,GPT,GOT,AKP,TP,and Alb.Plasma antioxidant stress capacity metabolites of GSH-Px,CAT,SOD,and MDA were unaffected（P>0.05）for 3 blocks of goats.（4）Levels of rumen pH,acetate,propionate,butyrate,total volatile fatty acid（TVFA）,and acetate/propionate（A/P）were unaffected（P>0.05）for LD relative to HD and CON.（5）Ruminal cellulolytic bacteria populations of Fibrobacter succinogenes,Ruminococcus flavefaciens,Butyrivibrio fibrisolvens and Ruminococcus albus were unaffected（P>0.05）among 3 treatments.HD and LD had higher（P<0.05）Firmicutes abundance than CON.There was no difference（P>0.05）in the adversity of rumen bacterial flora and other phylum and genus with relative content greater than 1%as DCAD decreased.Conclusion:lowering DCAD has no effect on rumen pH,VFA,rumen bacterial flora and microflora composition and abundance,therefore,would alter the rumen health and function.It is believed that dairy goats have higher hypocalcemia frequency than goats,therefore,on the basis of experiment 1,experiment 2 was carried out,with dairy goats served as experimental animals,to investigate the effects of reducing DCAD on the rumen fermentation and hypocalcemia prevention as well.Experiment 2:Effect of lowering DCAD on growth performance,humoral acid-base balance,blood gas,plasma Ca homeostasis,rumen fermentation parameters and microflora of dairy goatsExperiment design:Thirty nonpregnant Saanen dairy goats were randomly allocated to 3 blocks of 2 replications with 5 goats each.Animals were fed 1 of 3 diets with varying DCAD levels at+349（HD）,+120（CON）,and-167（LD）,respectively.The detected indicators included growth performance（DMI,ANG,ADG,F/G）,urine pH,blood pH,pO₂,pCO₂ and HCO₃^-;blood Na⁺,K⁺,Ca²⁺,Cl^-;plasma Ca,VDR,TRPV6,Mg,Glu,UN,GPT,GOT,AKP,TP,Alb,CAT,SOD,MDA,Cr;rumen pH,buffer capacity,VFA,NH₃-N,cellulases activity,cellulolytic bacteria,microflora composition and abundance,and the cumulative gas production of rumen fermentation in vitro and its fermentation parameters at 60 h.Results:（1）reducing DCAD had no effect（P>0.05）on DMI,ANG,ADG and F/G.（2）Urine pH in LD was lower（P<0.05）relative to HD and CON.（3）LD resulted in lower（P<0.05）blood pH over CON but not for pO₂,pCO₂ and HCO₃^-levels（P>0.05）.Blood[Ca²⁺]level in LD was increased（P<0.05）compared with HD.（4）LD resulted in higher plasma Ca over HD（P<0.05）.LD and CON had higher（P<0.05）plasma VDR level than HD.No difference（P>0.05）was observed for plasma TRPV6 levels for 3 treatments.LD resulted in higher（P<0.05）plasma AKP over HD.There was no effect（P>0.05）on plasma Mg,Glu,UN,TP,Alb,GPT,GOT,Cr and CAT,SOD,MDA levels for HD,CON,and LD.（5）Reducing DCAD had no effect（P>0.05）on levels of rumen pH,buffer capacity,acetate,propionate,butyrate,TVFA,A/P,NH₃-N,microcrystallinecellulose,xylanase,cellobiaseand carboxymethyl cellulose.（6）The relative abundances of ruminal Fibrobacter succinogenes,Ruminococcusflavefaciens,Butyrivibriofibrisolvensand Ruminococcus albus were nonsignificant（P>0.05）for DCAD variation.No difference（P>0.05）in the adversity of rumen bacterial flora and main phylum and genus were observed as DCAD decreased.（7）Cumulative gas production at 3 h,4 h,5 h,6 h,7 h,8 h,9 h,10 h,11 h,12 h,24 h,48 h were unaffected by DCAD variations.Reducing DCAD had no effect（P>0.05）on fermentation fluid pH,buffer capacity,acetate,propionate,butyrate,TVFA,A/P,NH₃-N,microcrystalline cellulose,xylanase,cellobiase and carboxymethyl cellulose levels.Conclusion:Lowering DCAD has no negative effect on rumen fermentation parameters,cellulolytic bacteria and microflora composition and abundance.It is reported that blood calcium concentration would increase when mammals were fed more Ca and Mg levels in the diet.Experiment 3 was focused on the effect of lowering DCAD plus Ca,Ca and Mg on blood Ca,and meanwhile,to evaluate whether reducing DCAD had negative effect on rumen fermentation function.Experiment 3:Effects of Lowering DCAD plus Ca,Ca and Mg on urine pH,plasma Ca homeostasis,rumen fermentation parameters and microflora of dairy goats.Experiment design:Twenty-seven nonpregnant Saanen dairy goats were randomly allotted to 3 blocks of 3 replications with 3 goats each.Diary goats were fed LD（-160）,LD plus Ca（LD-Ca;-151）;and LD plus Ca and Mg（LD-Ca-Mg;-155）,respectively.The Ca source was calcium carbonate（CaCO₃）,and the Mg source was magnesium oxide（MgO）.The detected indicators included urine pH,plasma Ca,VDR,TRPV6,Mg,rumen pH,buffer capacity,VFA,NH₃-N,cellulase activity,cellulolytic bacteria and microflora composition and abundance.Results:（1）Urine pH was unaffected for 3 blocks of goats（P>0.05）.（2）Plasma Ca,VDR and TRPV6 levels were unaffected by DCAD variations（P>0.05）.Plasma Mg level was higher（P<0.05）for LD-Ca-Mg relative to LD and LD-Ca.（3）LD-Ca-Mg resulted in lower（P<0.05）rumen NH₃-N level than LD and LD-Ca.No other difference（P>0.05）on rumen pH,buffer capacity,acetate,propionate,butyrate,TVFA,A/P,microcrystalline cellulose,xylanase,cellobiase and carboxymethyl cellulose were observed among 3 treatments.（4）The relative abundance of ruminal Fibrobacter succinogenes in LD-Ca-Mg was higher（P<0.05）relative to LD and LD-Ca.The relative abundance of Ruminococcus flavefaciens,Butyrivibrio fibrisolvens and Ruminococcus albus were unaffected（P>0.05）by DCAD alteration.No difference（P>0.05）in the adversity of rumen bacterial flora and main phylum and genus were observed among 3 groups.Conclusion:Reducing DCAD plus Ca,Ca and Mg could maintain plasma calcium homeostasis,and had no negative effect on rumen fermentation function and microflora composition and abundance.The above-mentioned results indicate that lowering DCAD is able to improve blood Ca concentration.Reducing DCAD plus Ca,Ca and Mg are beneficial to maintaining blood Ca homeostasis and have no negative effect on rumen fermentation and microflora.The unaffected rumen fermentation parameters by lowering DCAD establish its feasibility for hypocalcemia prevention of goats in the practice.