Effects Of Synchronizing Supply Of Dietary Energy And Nitrogen On Rumen Metabolism,Productive Efficiency And Performance In Dairy Cows

In the current dairy farming, feed utilization efficiency is very low, which caused serious environmental pollution. In this study, four different nutrient synchrony diets were formulated by changing processing method of the main ingredients (corn and soybean). A systematic research was given on the effects of synchronizing supply of dietary energy and nitrogen on rumen metabolism, productive efficiency and performance, which provided theoretical and practical basis for increasing feed utilization efficiency, reducing environmental pollution and improving milk quality. Because collection of ruminal contents is needed for rumen metabolism research, an oral stomach tube (OST) technique was fisrtly validated for the collection of ruminal contents; and then was applied to the subsequent in vivo experiment for study of rumen metabolism.1. Validation of the technique for ruminal content collection by oral stomach tube and its optimization (Experiment1)The objective of this experiment was to validate the technique for the collection of ruminal content by an OST. Six rumen-fistulated dairy cows were used in two trials. Firstly, the differences of ruminal fermentation parameters among rumen sites (cranial dorsal, cranial ventral, central, ventral, caudal dorsal and caudal ventral) were compared. The ruminal fluid was collected once a day for3consecutive days through rumen cannula (RC). The samples were analyzed for pH, volatile fatty acids (VFA), ammonia-nitrogen (NH3-N), sodium, potassium, calcium, chloride and phosphorus concentrations. The ruminal fermentation parameters varied significantly among rumen sites. Compared with the central or ventral rumen, the cranial dorsal rumen had significantly higher pH, NH3-N and sodium concentrations and lower acetate, propionate and butyrate concentrations, indicating that the sampling site may be one of the main factors contributing to the difference of ruminal fermentation parameters between the samples collected via the OST and RC. After that, the fermentation parameters of ruminal fluid collected via OST at two insertion depths (180or200cm) were compared with those of ruminal fluid collected via RC (ventral sac). Ruminal fluid was collected once a week at5to6hours after morning feeding. When the OST was inserted to a depth of180cm, the OST head was located in the cranial dorsal (atrium) of the rumen. The ruminal fluid collected via the OST had higher pH and sodium concentrations but lower VFA, potassium, calcium and phosphorus concentrations than that collected via RC. However, when the OST was inserted to a depth of200cm, the OST head could pass through the front rumen pillar and reach the central rumen for sampling. No differences were found in pH, VFA, NH3-N and ion concentrations between the samples collected via the two sampling methods. These results indicated that the OST should be inserted to reach the central rumen to obtain representative ruminal content.2. Effects of synchronizing supply of dietary energy and nitrogen on rumen fermentation, enzyme activity and microbial population in dairy cows (Experiment2)The objective of this experiment was to investigate the relationship between diets and rumen microorganisms and their interaction mechanism. Two types of corn (dry ground (DGC) and steam-flaked corn (SFC)) and two types of soybean meal (SBM)(solvent-extracted (SSBM) and heat-treated SBM (HSBM)) differing in their rate and extent of ruminal degradation (measured using in situ method) were used to formulate four diets. Twelve multiparous Holstein dairy cows (BW=594±31kg; days in milk=130±14d; milk yield=31.3±1.8kg) were used in a4×4Latin square design with a2×2factorial arrangement. Each period lasted for21days, including14d adaptation and a7d of data collection. Ruminal contents were collected using oral stomach tube (validated in experiment1) at approximately3h after morning feeding at d7of each data collection period and was analyzed for rumen fermentation characteristics, enzyme activity and microbial population. Synchronizing supply of dietary energy and nitrogen had no effects on these parameters. Corn types had greater influence on rumen metabolism than SBM types. Ruminal concentrations of NH3-N and acetate were greater, and total VFA and predicted methanes tended to be greater for DGC than SFC based diets. Xylanase activity was lower, and amylase activity tended to be lower for SFC than DGC based diets, but no difference was found in carboxymethyl cellulase activity. In microbial population, SFC based diets had lower methanogens and R.amylophilus, but higher S. bovis population, compared with DGC based diets. The SBM types differing in CP degradation have no effects on rumen fermentation, enzyme activity and microbial population. These results suggested that increasing rate of energy degradation could improve efficiency of rumen NH3-N utilization, reduce methanogens population and decrease methane emission.3. Effects of synchronizing supply of dietary energy and nitrogen on nutrient digestion, metabolism and productive performance in dairy cows (Experiment3)The objective of this study was to find out the best pattern of nutrient synchrony that can improve microbial protein synthesis and productive performance and elucidate its mechanism. The experiment design was the same as Experiment2. Samples of milk, feces, urine and blood were collected during sampling period. Synchronizing supply of energy and nitrogen resulted in lower concentrations of urea N in milk (MUN) and blood (BUN), but had no effects on nutrient digestion, N metabolism and productive performance. Dietary energy degradability had more influences on productive performance and nutrient utilization than protein degradability. The cows fed SFC had lower DMI than DGC based diets. However, milk yield was not affected by corn types, resulting in higher feed utilization efficiency for cows fed SFC than DGC based diets. Milk ptotein, milk fat and milk lactose yield were not influenced by corn types. Apparent total tract digestibility of starch was greater for SFC than DGC based diets. However, apparent digestibilities of dry matter, organic matter, crude protein, and neutral detergent fiber were not influenced by corn types. Efficiency of N utilization (milk N/total N intake) was greater and excretion of urine urea N and fecal N tended to be lower for SFC than DGC based diets. Concentration of BUN was lower, while insulin concentration tended to be greater for SFC than DGC based diets. Other parameters were not influenced by corn types. Soybean meal types differing in CP degradability only had influence on few parameters. Cows fed HSBM had significant lower microbial cell protein mass than SSBM based diets did. These results suggested that increasing rate of energy degradation could improve efficiency of feed and N usage.In summary, the OST technique was optimized for ruminal fluid collection, and effectively applied to the subsequent in vivo experiments for ruminal metabolism research. Under the condition of this study, synchronizing supply of energy and nitrogen did not have great effects on rumen fermentation, MCP yield and productive performance in mid-lactation dairy cows. Energy degradability had greater influences than protein degradability on rumen metabolism and productive performance in dairy cows. Increasing energy degradability could properly improve feed utilization efficiency and contribute to reduce environmental pollution.