Effects Of Different Sources Of Roughage On Growth Performance,Digestion And Metabolism,Rumen Fermentation And Microflora Of Calves

The aim of this experiment was to explore the suitable source of roughage for feeding weaned calves and to provide scientific theoretical basis and practical guidance for healthy breeding of calves in animal husbandry.The routine nutritional values of peanut vine,oat hay and alfalfa hay were measured,and then the protein and carbohydrate components of 3 different roughage sources were compared using Cornell net carbohydrate-protein system.The effects of 3 different roughages on growth and development,digestion and metabolism,blood biochemical parameters,rumen fermentation and microflora of weaned Holstein calves were studied by a feeding trial.The fifty-four healthy weaned Holstein male calves（age = 70 ± 2.54 d,body weight = 77.50 ± 5.07 kg）were randomly blocked into 3 treatment groups according to body weight and age,with 18 calves in each group.The roughage source of dietary in each group was peanut vine（PV）,oat hay（OH）and alfalfa hay: Oat hay =1:1（AO）.The calves were required to adapt to the diets within 7-day,followed by a 60-day feeding experiment.The feed intake of calves was measured daily,body weight（BW）and body structure indexes of calves were measured every 15 days,and the average daily feed intake（ADFI）,average daily gain（ADG）and feed/ gain（F/G）were calculated.On d 60 of the trial period,each treatment group randomly selected 9 calves,jugular vein blood collected was used for the determination of serum alanine aminotransferase（ALT）,aspartate aminotransferase（AST）activity and total protein（TP）,albumin（ALB）,globulin（GLB）,urea nitrogen（UN）,glucose（GLU）,total cholesterol（CHOL）,triglyceride（TG）,high density lipoprotein（HDL-C）,low density lipoprotein（LDL-C）.Rumen fluid was collected to determine rumen fermentation parameters and microflora.The digestion and metabolism tests were performed on the 60 th day of the trial period.The results were as follows:（1）The contents of crude protein（CP）and neutral detergent fiber（NDF）in the 3roughages are high,which could meet the CP,NDF and other nutrients required by the growth and production of ruminants.Compared with oat hay and alfalfa hay,peanut vine has the potential as roughage for ruminants.（2）The final weight,ADFI and ADG of calves in PV and AO groups were significantly higher than those in OH group（P < 0.05）,and the ratio of F/G of calves in PV group was the lowest.On day 60,the body height and chest girth of calves in PV group were significantly higher than those in OH group（P < 0.01）.Feeding peanut vine improved the economic benefit of calf rearing,reduced the cost of feed weight gain（P < 0.01）,and increased the profit margin of calf rearing.（3）The apparent digestibility of dry matter and biological value of nitrogen in PV group were significantly higher than those in OH group（P < 0.05）;Meanwhile,the apparent digestibility of organic matter and calcium,digestible energy,absorbed nitrogen and deposited nitrogen of calves in PV group were significantly higher than those in OH group（P < 0.01）.（4）The contents of CHOL,HDL-C,LDL-C and GLU in blood of calves in PV group were significantly higher than those in OH and AO groups（P < 0.01）,and the contents of UN in PV group was significantly lower than that in OH and AO groups（P < 0.01）.（5）Rumen fluid p H of calves fed with peanut vine and oat hay was significantly increased（P < 0.05）.In addition,the concentration of propionate in rumen fluid of calves in PV and AO groups was significantly increased（P < 0.05）.The relative abundance of Bacteroidetes and Firmicutes in phylum level was higher,but the difference was not significant（P > 0.05）.At the genus level,the Rikenellaceae_RC9_gut_group,Shuttleworthia,Ruminococcacae,Prevotella and Succiniclasticum were the key rumen genera in this study.The relative abundance of Rikenellaceae_RC9_gut_group was significantly negatively correlated with BW and ADG（P < 0.05）.The relative abundance of Shuttleworthia was significantly positively correlated with BW,ADG,ADFI,body length and propionate concentration（P < 0.05）,but negatively correlated with ADF and calcium digestibility,ALT,AST and ALB contents and p H（P < 0.05）.The relative abundance of Ruminococcace AE_UCG-014 was significantly negatively correlated with BW and body height（P < 0.05）,and Ruminococcus₂ was significantly positively correlated with GLB content（P < 0.05）.The relative abundance of Ruminococcus₁ was positively correlated with butyrate and NH3-N concentration（P < 0.05）.The relative abundance of Prevotella₁was positively correlated with NDF digestibility（P < 0.05）.The Prevotella₇ was significantly negatively correlated with ALT,CHO,HDL-C and LDL-C（P < 0.05）,but significantly positively correlated with TP（P < 0.05）.The relative abundance of Prevotella₇ was negatively correlated with butyrate concentration（P < 0.05）.The Succiniclasticum was significantly negatively correlated with AST,CHO,HDL-C and LDL-C（P < 0.05）,and was negatively correlated with butyrate concentration（P < 0.05）.These key bacteria may play important roles in carbohydrate transport and metabolism,amino acid transport and metabolism,and energy production and transport,and are expected to be the target bacteria for regulating rumen function.In conclusion,compared with alfalfa hay and oat hay,peanut vine had similar nutrient components,but the feed intake of calves was increased and the nutrient apparent digestibility of calves was increased during production,even better than the oat hay and mixed feeding of oat hay and alfalfa hay.At the same time,the application of peanut vine improved the rumen fermentation pattern of calves.The Rikenellaceae_RC9_gut_group,Shuttleworthia,Ruminococcacae,Prevotella and Succiniclasticum in this experiment could be used as the key target bacteria of roughage regulating the rumen function of weaned calves.In conclusion,peanut vine could be the main source of roughage for calves at 2-4months of age.