Effects of Candida utilis Supplemental Level in High Concentrate Total Mixed Ration on in Vitro Ruminal Fermentation Characteristics and Fiber Degradation

In vitro ruminal fermentation test and real-time gas production recording technique were combined to determine effects of Candida utilis(CU) supplemental level in high concentrate total mixed ration on in vitro ruminal fermentation characteristics and fiber degradation.Ruminal fluid was collected from five lactating Holstein cows.The CU was supplemented at levels of 0(control group),0.53×10,1.07×10,1.60×10,2.13×10 and 2.67×10 CFU/mL,respectively.The indices of 72 h accumulative gas production,kinetic parameters of gas production and ruminal fermentation characteristics were determined.The results showed as follows:with the increase of CU supplemental level,in vitro disappearance rates of nutrients(dry matter,neutral detergent fiber and acid detergent fiber) in the substrate,gas production at different time points,72 h accumulative gas production,kinetic parameters of gas production(theoretical maximum gas production and time of reaching 1/2 of it) and microbial protein and total volatile fatty acids concentrations as well as propionic acid,valeric acid and branch-chain fatty acids contents were significantly increased(P 0.050 or P 0.001),whereas acetic acid and butyric acid contents and methane production were significantly decreased(P 0.001).In summary,the supplementation of CU can increase degradation and fermentation of fiber by ruminal microbes.Under conditions of the present total mixed ration,the optimal supplemental level of CU is 2.67×106 CFU/mL.