The objectives of the present research were to investigate the changes in duodenal bacterial nitrogen flow and volatile fatty acids (VFAs) with the different dietary ratios of forage and concentrate (F:C) and to determine the relationship of duodenal bacterial nitrogen flow and volatile fatty acids with ruminal odd- and branched-chain fatty acids (OBCFAs). The experimental design was a 3 x 3 Latin square. Three rumen- and duodenal-fistulated dry Holstein cows were fed three rations with different dietary ratios of forage and concentrate (F:C; 30:70, 50:50 and 70:30). The rumen and duodenal samples were collected every two hours over 3 consecutive days of each sampling period. The determined parameters included OBCFA profiles in the rumen, duodenal bacterial nitrogen flow, VFAs, ammonia nitrogen (NH3-N) content and pH. The results showed that ruminal OBCFA contents, duodenal bacterial nitrogen flow, VFAs, ammonia nitrogen (NH3-N) and pH were significantly influenced by the different dietary F:C ratios and sampling times (P < 0.01). The ruminal contents of C15:0 and C15:0 + C17:0 were positively related to the molar proportions of duodenal acetate but negatively correlated with the propionate, butyrate and NH3-N contents (P < 0.05). The ruminal C15:0/C17:0 ratio was positively correlated with the proportions of acetate and pH (P < 0.05) but negatively correlated with VFA contents in the duodenum (P < 0.05). The duodenal bacterial nitrogen flow was positively correlated with ruminal C11:0 and isoC17:0 contents (P < 0.05) but negatively correlated with C15:0/C17:0 and isoC15:0/isoC17:0 (P < 0.05). These findings suggested that some ruminal OBCFAs are closely related to the microbial nitrogen and volatile fatty acids in duodenal flow and significantly changed with the proportion of forage in diets. Ruminal OBCFA have the potential to predict microbial nitrogen flow, and the predicted equations for duodenal microbial nitrogen flow were established with OBCFAs in the rumen.

The purpose of this research was to evaluate whether relationships exist between odd- and branched-chain fatty acids (OBCFAs) originating from milk fat and the corresponding data of ruminal fermentation parameters, microbial populations, and base contents that were used to mark microbial protein in rumen. Nine lactating Holstein dairy cows with similar body weights and parity were selected in this study, and the samples of rumen and milk were collected at the early, middle, and late stages, respectively. The rumen and milk samples were collected over three consecutive days from each cow, and the ruminal and milk OBCFA profiles, ruminal fermentation parameters, bacterial populations, and base contents were measured. The results showed that the concentrations of OBCFAs, with the exception of C11:0 and C15:0, were significantly different between milk and rumen (p < 0.05). The concentrations of anteiso-fatty acids in milk were higher than those in rumen, and the contents of linear odd-chain fatty acids were higher than those of branched-chain fatty acids in both milk and rumen. Significant relationships that existed between the concentrations of C11:0, iso-C15:0, anteiso-C15:0, C15:0, and anteiso-C17:0 in rumen and milk (p < 0.05). The total OBCFA content in milk was positively related to the acetate molar proportion but negatively correlated with isoacid contents (p < 0.05). The populations of Ruminococcus albus, R. flavefacients, and Eubacterium ruminantium were significantly related to milk C13:0 contents (p < 0.05). The adenine/N ratio was negatively related to milk OBCFA content (p < 0.05) but positively associated with the iso-C15:0/iso-C17:0 ratio (p < 0.05). Milk OBCFAs were significantly correlated with ruminal fermentation parameters, ruminal bacterial populations, and base contents. Milk OBCFAs had the potential to predict microbial nitrogen flow, and the prediction equations for ruminal microbial nitrogen flow were established for OBCFAs in dairy milk.

OBJECTIVE:This study aims to identify the relationship between odd- and branched-chain fatty acids (OBCFAs) and microbial nucleic acid bases in the rumen, and to establish a model to accurately predict microbial protein flow by using OBCFA.METHODS:To develop the regression equations, data on the rumen contents of individual cows were obtained from 2 feeding experiments. In the first experiment, 3 rumen-fistulated dry dairy cows arranged in a 3×3 Latin square were fed diets of differing forage to concentration ratios (F:C). The second experiment consisted of 9 lactating Holstein dairy cows of similar body weights at the same stage of pregnancy. For each lactation stage, 3 cows with similar milk production were selected. The rumen contents were sampled at 4 time points of every two hours after morning feeding 6 h, and then to analyse the concentrations of OBCFA and microbial nucleic acid bases in the rumen samples.RESULTS:The ruminal bacteria nucleic acid bases were significantly influenced by feeding diets of differing forge to concentration ratios and lactation stages of dairy cows (p<0.05). The concentrations of OBCFAs, especially odd-chain fatty acids and C15:0 isomers, strongly correlated with the microbial nucleic acid bases in the rumen (p<0.05). The equations of ruminal microbial nucleic acid bases established by ruminal OBCFAs contents showed a good predictive capacity, as indicated by reasonably low standard errors and high R-squared values.CONCLUSION:This finding suggests that the rumen OBCFA composition could be used as an internal marker of rumen microbial matter.

Objective This trial was performed to examine the effects of ruminally degradable starch (RDS) levels in total mixed ration (TMR) with low corn-based starch on the milk production, whole-tract nutrient digestibility and nitrogen balance in dairy cows. Methods Eight multiparous Holstein cows (body weight [BW]: 717±63 kg; days in milk [DIM]: 169±29) were assigned to a crossover design with two dietary treatments: a diet containing 62.3% ruminally degradable starch (% of total starch, low RDS) or 72.1% ruminally degradable starch (% of total starch, high RDS). Changes to the ruminally degradable levels were conducted by using either finely ground corn or steam-flaked corn as the starch component. Results The results showed that dry matter intake, milk yield and composition in dairy cows were not affected by dietary treatments. The concentration of milk urea nitrogen was lower for cows fed high RDS TMR than low RDS TMR. The whole-tract apparent digestibility of neutral detergent fiber, acid detergent fiber and crude protein decreased, and that of starch increased for cows fed high RDS TMR over those fed low RDS TMR, with no dietary effect on the whole-tract apparent digestibility of dry matter and organic matter. The proportion of urinary N excretion in N intake was lower and that of fecal N excretion in N intake was higher for cows fed high RDS TMR than those fed low RDS TMR. The N secretion in milk and the retention of N were not influenced by the dietary treatments. Total purine derivative was similar in cows fed high RDS TMR and low RDS TMR. Consequently, estimated microbial N flow to the duodenum was similar in cows fed high RDS TMR and low RDS TMR. Conclusion Results of this study show that ruminally degradable starch levels can influence whole-tract nutrient digestibility and nitrogen balance in dairy cows fed low corn-based starch diets, with no influence on performance.

This trial was performed to examine the effects of different ruminally degradable starch levels in the diet with low corn-based starch on in vitro ruminal fermentation.Three Holstein cows fitted with permanent rumen fistulas were used as the donor of rumen fluid.Diets with different ruminally degradable starch levels were used as substrates, and the changes of gas production and ruminal fermentation parameters during 48 h incubation were determined using in vitro gas production method, and the ruminal microflora change during 24 h incubation was also determined.The results showed as follows: 1) with the ruminally degradable starch level increasing, gas production (GP), potential gas production (a+b) and gas production rate constant for "gas production from the slowly soluble fraction (b)" (c) were linearly increased (P<0.05), the gas production from the immediately soluble fraction (a) was linearly decreased (P<0.05), and the dry matter digestibility was linearly increased after 48 h in vitro incubation (P<0.05).2) With the ruminally degradable starch level increasing, fermentation fluid microprotein (MCP), acetate, propionate, butyrate and total volatile fatty acids (TVFA) concentrations were linearly increased after 48 h in vitro incubation (P<0.05), but the pH and ammoni anitrogen concentration were not significantly changed (P>0.05).3) With the ruminally degradable starch level increasing, the relative counts of R.albus and R.amylophilus in fermentation fluid after 24 h in vitro incubation were linearly increased (P<0.05), while the relative counts of R.flavefacien, F.succinogenes, B.fibrisolvens, S.bovis and S.amylolytica had no significant changes (P>0.05).It is concluded that incraesing ruminally degradable starch level can improve ruminal fermentation under the condition of low starch diet.

This trial was performed to examine the effects of different ruminally degradable starch levels on lac?tation performance, nutrient apparent digestibility and nitrogen balance of dairy cows fed high starch diets. Ten multiparous Holstein cows [(average lactation days: (214±38) d; average milk yield: (26.2±2.4) kg/d;average body weight: (727±65) kg] were randomly assigned to 2 groups, and each group had 5 dairy cows. Two types of diets with different ruminally degradable starch levels were formulated, one of them contained 62.3% ( percentage of total starch) ruminally degradable starch which named as low?ruminally degradable starch diet ( L?RDS) , and the other contained 72.1% ( percentage of total starch) ruminally degradable starch which named as high?ruminally degradable starch diet ( H?RDS) . A crossover experimental design was applied. There were two experimental periods, the transition period lasted for 7 d, and each period lasted for 21 d (14 d of pretrial period, and 7 d of sampling period). The results showed as follows:1) the apparent digesti?bility of starch and organic matter was significantly increased (P<0.05), the apparent digestibility of neutral detergent fiber and acid detergent fiber was significantly decreased ( P<0.05) , and the apparent digestibility of dry matter had a rising trend (P=0.07) for H?RDS group compared with L?RDS group, but no significant difference in the apparent digestibility of crude protein among them (P>0.05). 2) Compared with L?RDS group, urinary urea?nitrogen and the proportion of urinary urea?nitrogen in nitrogen intake had a decrease trend for H?RDS group (P=0.09). The nitrogen intake, milk nitrogen, urinary nitrogen, fecal nitrogen, nitrogen retention and the proportions of them in nitrogen intake were not significantly affected by dietary ruminally de?gradable starch level (P>0.05), and the urinary excretion of purine derivatives and microbial protein yield were also not significantly affected by dietary ruminally degradable starch level ( P>0.05) . 3) Dry matter in?take, milk yield and milk composition of dairy cows were not significantly affected by dietary ruminally de?gradable starch level ( P>0.05) . Results of this study show that different ruminally degradable starch levels can affect the nutrient apparent digestibility of dairy cows fed high starch diets, with no significant influences on lactation performance and nitrogen balance.

This experiment was conducted to investigate the effects of feeding steam-flaked corn in varying proportions on ruminal acidity. This experiment was designed as a 4*4 Latin square using four Holstein cows in dry period with rumen-cannulated. Diets were chemically similar but varied in steam-flaked corn added(0%, 30%, 60%, 100%). They were divided into 4 groups (4 trial time) and first 14 d to adjust the diet and last 12 d for experiments. The results showed that reducing steam-flaked corn ritio of diets, declined ruminal pH significantly(P<0.01); As increasing steam-flaked corn ritio of diets, the propionate acid content and TVFA (total volatile fatty acids) content is significantly higher than three other groups(P<0.01), and acetate/propionate ratio of high steam-flaked corn added significantly lower than three other groups(P<0.01),it had changed the ruminal fermentation type. Therefore, the effects of feeding steam-flaked corn in varying proportions on ruminal pH in varying time had difference significantly, and so were the propionate acid, it had changed the ruminal fermenta?tion type. This study indicates that adding steam-flaked corn in dairy diets play an active role.

This experiment was conducted to investigate the effects of diet supplementation with Se-yeast on blood Se contents and anti-oxidation performance and provide data for Se-yeast application in prepartum dairy cows .A total of 20 Chinese Holstein dairy cows whose body condition,parity and the expected calving period were similar were randomly divided into four groups(A,B,C and D group):A group as the control group was fed basic diet,B group was basic diet supplemented with 2.4 g Se-yeast/day,C group was fed basic diet supplemented with 4.8 g Se-yeast/day,D group diet was basic diet supplemented with 7.2 g Se-yeast/day.The results showed that:the Se-yeast could in crease blood selenium contents and improve anti-oxidation performance.It was concluded that the supplementation of Se-yeast 2.4 g/day had better improvement on blood Se contents and anti-oxidation performance.

本研究旨在通过给围产前期奶牛饲喂不同水平的酵母硒,探讨酵母硒对围产前期奶牛全血硒浓度和血清抗氧化能力的影响,为酵母硒在国产前期奶牛养殖的应用提供参考依据.试验选取20头体况、胎次和预产期相近的奶牛,分为4组(A、B、C和D组),A组(对照组)饲喂基础日粮,B、C和D组在基础日粮基础上分别饲喂酵母硒2.4、4.8 g/d和7.2 g/d.对试验牛群血样分析表明:在本试验条件下,综合考虑全血硒浓度和抗氧化指标,饲喂酵母硒2.4 g/d(硒含量0.49 mg/kg DM)的效果最好.