Effects Of Dietary Neutral Detergent Fiber And Starch Ratio On Milk Composition Synthesis And Rumen Metabolism In Dairy Cows

Carbohydrate is the major part of the diet in dairy cows, which was closely connected with the metabolism of the three major nutrients(carbohydrate, protein and fat). Dietary carbohydrate can be diveided into structural and non-structural parts, which neutral detergent fiber(NDF) and starch are the major components of structural and non-structural carbohydrates according to the chemical composition. Therefore, dietary NDF and starch content could reflect the composition of dietary carbohydrate. This study was designed to investigate the effect of dietary carbohydrate on milk production and component synthesis, and furthermore reveal the nutritional foundation, which could provide scientific basis for dietary carbohydrate efficient utilization in dairy practice.1. Meta-analysis was conducted to investigate the effect of dietary NDF and starch content on milk production and component synthesis in dairy cows. 26 published papers were collected including 115 experimental treatments. The correlationship and regression analysis was conducted between dietary NDF, starch and NDF: starch ratio and milk production and component synthesis. Compared with dietary NDF and starch content, NDF:starch ratio was highly correlated with DMI(r =-0.799, P < 0.01), milk production(r =-0.730, P < 0.01), milk fat content(r = 0.664, P < 0.01) and milk protein content(r =-0.788, P < 0.01). Significant regression relationship was observed between dietary NDF:starch ratio and DMI, milk yield, milk fat content, milk protein content, and milk protein and lactose yields. Therefore, Meta-analysis results indicated that NDF:starch ratio could be applied to reflect the dietary carbohydrate composition, which should be payed more attention when formulating diets.2. This study was designed to investigate the effect of dietary NDF:starch ratio on milk production and components synthesis. Eight primiparous dairy cows including four rumen cannulated animals were assigned to 4 total mixed rations in a replicated 4×4 Latin square design. The duration of each period was 21 d including 14 d adaptation period and 7d sampling period. The dietary treatments were achieved by altering the forage(corn silage and oat hay) and concentrate(corn) to achieve the different NDF:starch ratios: diet 1( NDF: starch = 0.86), diet 2(NDF: starch = 1.18), diet 3(NDF: starch = 1.63) and diet 4(NDF: starch = 2.34). The results showed that milk yield, milk protein content and yield and lactose content and yield significantly decreased as dietary NDF: starch ratio increased. The digestibility of dry matter, organic matter, crude protein, neutral detergent fiber and ether extract decreased and starch digestibility tended to increase. Rumen microbial protein and metabolizable protein decreased when dietary NDF:starch ratio increased. Blood glucose content linearly decreased and blood NEFA content were increased as dietary NDF:starch ratio increased. The results showed that the dietary NDF:starch ratio could have significant impact on milk yield and components synthesis.3. This study was designed to investigate the effect of dietary NDF:starch ratio on the rumen environment. Nutrients degradation, rumen fermentation and microbe community was analyzed. The results showed that dietary dry matter and neutral detergent fiber degradation rate linearly decreased as dietary NDF:starch ratio increased. However, dietary crude protein degradation showed no significant difference. Ruminal p H increased as dietary NDF:starch ratio increased, which the cows in Diet 1 treatment suffered subacute rumen acidosis(SARA). The result of regression analysis revealed that the risk of SARA increased when dietary NDF:starch ratio was below 1.08. Rumen fermentation pattern was affected by dietary NDF:starch ratio, which rumen fermentation was shifted from propionate to acetate pattern as dietary NDF:starch ratio increased. Cellulolytic bacteria of Fibrobacter succinogene showed the increasing trend and lactic acid utilization bacteria of Megasphaera elsdenii linearly decreased as dietary NDF:starch ratio increased. The results showed that dietary NDF:starch ratio could affect rumen enviroment and rumen health, which could be used as an nutritional indicator to modulate rumen environment.4. The study was designed to investigate the effect dietary carbohydrate composition on nitrogen efficiency. The experiment design was the same as the experiment two. The correlationship and nitrogen efficiency analysis was conducted among dietary CP intake, MCP, MP and milk protein secretion.. The results revealed that crude protein had the dominant effect on milk protein synthesis, which was followed by MP and MCP. Quadratic effect of milk nitrogen efficiency was observed in dietary CP intake conversion to milk protein. Increasing trend of linear effect of nitrogen efficiencywas observed in dietary CP intake conversion to MP as dietary NDF:starch ratio improved. Trend of quadratic effect of nitrogen efficiency was observed in MP conversion to milk protein. No treatment effect was observed in the efficiency of MP conversion to milk protein and crude protein conversion to MP. When dietary NDF:starch ratio was 1.71, the efficiency of dietary CP intake conversion to milk protein reached the highest level of 27.6%. Therefore, it suggested that reasonable dietary carbohydrate composition(NDF:starch ratio) has profound sense in improving nitrogen efficiency.5. This study was designed to investigate the effect of dietary NDF: starch ratio on rumen morphological structure and gene expression of cell growth and metabolism of epithelial cells. The experiment design was the same as the experiment two. Rumen epithelial papilla was collected from rumen cannulated cows. Gene expression was detected with quantitative real-time PCR. The results showed that the thickness of stratum spinosum and basale increased as dietary NDF:starch ratio increased. Gene expression of NHE4 and HMGCS decreased linearly when dietary NDF:starch ratio increased, which indicated that dietary carbohydrate composition could affect the VFA absorption and metabolism. As dietary NDF:starch ratio increased, gene of IGFBP5 expression decreasd and IGFBP6 expression increased. The results indicated that dietary carbohydrate composition could affect rumen epithelial cell morphology and related genes expression.In summary, dietary NDF and starch were the important components of carbohydrate. Meta analysis showed that dietary NDF: starch ratio was highly related with milk yield and components synthesis. Dietary NDF:starch ratio could affect rumen environment, rumen epithelial structure and related genes expression. Therefore, dietary NDF:starch can be considered as a nutritional indicator to reflect the carbohydrate composition when formulating diets, but also can be applied as indicator to evaluate rumen health risk assessment.