日粮能氮释放同步性对奶牛瘤胃代谢、生产效率与性能的影响研究
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摘要
针对当前奶牛养殖过程中所存在的饲料利用效率低,环境污染严重问题,本研究通过变换奶牛日粮主要能量原料(玉米)和蛋白原料(豆粕)加工方式,配制四种能氮同步化程度不同的日粮,系统研究了不同能氮同步释放日粮对奶牛瘤胃代谢、生产效率与性能的影响,为提高饲料利用效率、减少环境污染及改善牛奶品质提供了理论实践依据。鉴于瘤胃代谢研究需要采集瘤胃内容物,本研究首先优化了瘤胃导管(OST)取瘤胃内容物技术,为后续健康奶牛瘤胃代谢研究提供了有效技术手段。
1、瘤胃导管取瘤胃内容物技术评价及优化(试验一)
本试验的目的是通过两部分内容的研究对瘤胃导管取瘤胃内容物技术进行优化。首先比较了瘤胃不同位点瘤胃发酵参数的差异,通过瘤胃瘘管(RC)采集六头奶牛不同位点瘤胃液,每天采集一次,连采三天,分析瘤胃液pH值、VFA、NH3-N、Na、 K、Ca、Cl和P离子浓度。试验结果发现,瘤胃不同位点的瘤胃液发酵参数存在差异,与其它位点(前腹盲囊、瘤胃背囊、瘤胃腹囊、后背盲囊、后腹盲囊)相比,前背盲囊瘤胃液pH值、氨氮及Na离子浓度较高,乙酸、丙酸及丁酸浓度较低。因此,推测瘤胃导管的插入深度有可能影响所采集瘤胃液的发酵参数。然后,对OST不同插入深度(180或200cm)采集瘤胃液与通过RC(腹囊)所采集瘤胃液的发酵参数进行了对比。晨饲后5-6h采集六头奶牛瘤胃液,每周采集一次。试验结果发现,当插入深度为180cm时,瘤胃导管探头处于瘤胃前背盲囊(瘤胃前庭)的位置,OST所取瘤胃液pH值、Na离子浓度高于RC所取瘤胃液,但VFA、K、Ca和P离子浓度低于RC所取瘤胃液；当插入深度为200cm时,瘤胃导管探头可以穿过瘤胃前肉柱到达瘤胃中部,OST所取瘤胃液与RC所取瘤胃液pH值、VFA、氨氮及各离子浓度差异不显著。结果说明,OST的插入深度影响瘤胃发酵参数,使用OST取成年奶牛瘤胃内容物时,为取得具有代表性的样品,应插入瘤胃中部(插入深度为200cm)取样。
2、日粮能氮释放同步性对奶牛瘤胃发酵、微生物酶活及菌群组成的影响(试验二)
本试验的目的是阐明不同能氮同步释放模式与瘤胃微生物的相互关系及作用机制。根据不同加工方式玉米(蒸汽压片玉米和粉碎玉米)或豆粕(浸提豆粕和热处理豆粕)瘤胃降解率不同(尼龙袋法测定),采用2×2因子组合配制出四种能氮同步化程度不同的日粮用于体内试验。12头经产荷斯坦奶牛(体重=594±31kg;泌乳天数=130±14d;产奶量=31.3±1.8kg),进行4×4重复拉丁方设计,试验分四期,每期21天(前14天为适应期,后7天为采样期)。每期采样期第7天,采用试验一已优化的瘤胃导管技术在晨饲后3h采集瘤胃内容物,用于瘤胃发酵参数、酶活和微生物菌群组成分析。在本试验条件下,日粮能氮同步调控对瘤胃发酵参数、微生物酶活及数量方面没有表现出同步化效应；而不同加工方式玉米对瘤胃代谢的影响较大,在发酵参数方面,饲喂蒸汽压片组奶牛瘤胃液氨氮、乙酸浓度及乙丙比显著低于饲喂粉碎玉米组奶牛,总VFA浓度和CH4估测值较饲喂粉碎玉米组奶牛有降低的趋势,但瘤胃pH、丙酸和丁酸浓度差异不显著；在酶活性方面,饲喂蒸汽压片组奶牛瘤胃内容物木聚糖酶活性显著低于饲喂粉碎玉米组,淀粉酶活性也较饲喂粉碎玉米组奶牛有降低的趋势,但羧甲基纤维素酶活性差异不显著；在微生物菌群组成方面,蒸汽压片玉米处理组日粮奶牛瘤胃内容物甲烷菌、嗜淀粉瘤胃杆菌数量显著低于粉碎玉米组日粮处理组,而牛链球菌数量显著高于粉碎玉米日粮处理组；不同加工方式豆粕日粮对奶牛各瘤胃发酵参数、微生物酶活及数量没有显著影响。本研究结果说明,增加日粮能量释放速率能够提高瘤胃氨氮利用效率,并通过抑制甲烷菌数量减少甲烷排放。
3、日粮能氮释放同步性对奶牛营养物质消化、代谢及生产性能的影响(试验三)
本试验的目的是找出能够增加微生物蛋白合成效率、提高动物生产性能的最佳能氮同步释放模式并阐明其机理。试验设计同试验二。在采样期采集奶样、饲料样、粪样、尿样、血样。结果发现,不同能氮同步释放日粮仅在MUN和BUN浓度方面表现出了同步化效应,但对其他营养物质消化、氮代谢及生产性能参数没有影响；不同加工方式玉米日粮对奶牛影响比较大。在生产性能方面,与饲喂含粉碎玉米日粮奶牛相比,饲喂含蒸汽压片玉米日粮奶牛DMI降低,但产奶量不受影响,从而导致饲喂蒸汽压片玉米组奶牛饲料转化效率显著提高。乳蛋白、乳脂肪及乳糖产量均不受玉米类型的影响;蒸汽压片玉米组日粮奶牛淀粉全肠道表观消化率显著高于粉碎玉米组,但对其他营养成分表观消化率没有影响；与饲喂粉碎玉米组奶牛相比,饲喂蒸汽压片玉米组奶牛氮利用效率(乳氮排出量/总氮摄入量)显著增加,尿中尿素含量及粪氮排出量都有降低的趋势；与饲喂粉碎玉米组奶牛相比,饲喂蒸汽压片组奶牛血清胰岛素含量有升高的趋势,血浆尿素氮浓度显著降低,但对其他血液各生化指标没有显著影响；不同加工方式豆粕仅对部分参数存在影响,与浸提豆粕日粮组相比,热处理豆粕组奶牛微生物蛋白合成量显著降低。本试验结果表明,提高日粮能量释放速率能够提高饲料转化率及氮利用效率。
综上所述,瘤胃导管(OST)取瘤胃液技术的优化,为奶牛瘤胃代谢研究提供了有效的技术手段；日粮能氮同步调控对泌乳中期奶牛瘤胃发酵、微生物蛋白合成及生产性能方面没有表现出预期的同步化效应；相较于蛋白质降解速率,日粮能量降解速率对于奶牛瘤胃代谢及生产性能的影响更大,表明适当增加日粮能量降解速率,可以提高饲料转化效率,减少环境污染。
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.
1、瘤胃导管取瘤胃内容物技术评价及优化(试验一)
本试验的目的是通过两部分内容的研究对瘤胃导管取瘤胃内容物技术进行优化。首先比较了瘤胃不同位点瘤胃发酵参数的差异,通过瘤胃瘘管(RC)采集六头奶牛不同位点瘤胃液,每天采集一次,连采三天,分析瘤胃液pH值、VFA、NH3-N、Na、 K、Ca、Cl和P离子浓度。试验结果发现,瘤胃不同位点的瘤胃液发酵参数存在差异,与其它位点(前腹盲囊、瘤胃背囊、瘤胃腹囊、后背盲囊、后腹盲囊)相比,前背盲囊瘤胃液pH值、氨氮及Na离子浓度较高,乙酸、丙酸及丁酸浓度较低。因此,推测瘤胃导管的插入深度有可能影响所采集瘤胃液的发酵参数。然后,对OST不同插入深度(180或200cm)采集瘤胃液与通过RC(腹囊)所采集瘤胃液的发酵参数进行了对比。晨饲后5-6h采集六头奶牛瘤胃液,每周采集一次。试验结果发现,当插入深度为180cm时,瘤胃导管探头处于瘤胃前背盲囊(瘤胃前庭)的位置,OST所取瘤胃液pH值、Na离子浓度高于RC所取瘤胃液,但VFA、K、Ca和P离子浓度低于RC所取瘤胃液；当插入深度为200cm时,瘤胃导管探头可以穿过瘤胃前肉柱到达瘤胃中部,OST所取瘤胃液与RC所取瘤胃液pH值、VFA、氨氮及各离子浓度差异不显著。结果说明,OST的插入深度影响瘤胃发酵参数,使用OST取成年奶牛瘤胃内容物时,为取得具有代表性的样品,应插入瘤胃中部(插入深度为200cm)取样。
2、日粮能氮释放同步性对奶牛瘤胃发酵、微生物酶活及菌群组成的影响(试验二)
本试验的目的是阐明不同能氮同步释放模式与瘤胃微生物的相互关系及作用机制。根据不同加工方式玉米(蒸汽压片玉米和粉碎玉米)或豆粕(浸提豆粕和热处理豆粕)瘤胃降解率不同(尼龙袋法测定),采用2×2因子组合配制出四种能氮同步化程度不同的日粮用于体内试验。12头经产荷斯坦奶牛(体重=594±31kg;泌乳天数=130±14d;产奶量=31.3±1.8kg),进行4×4重复拉丁方设计,试验分四期,每期21天(前14天为适应期,后7天为采样期)。每期采样期第7天,采用试验一已优化的瘤胃导管技术在晨饲后3h采集瘤胃内容物,用于瘤胃发酵参数、酶活和微生物菌群组成分析。在本试验条件下,日粮能氮同步调控对瘤胃发酵参数、微生物酶活及数量方面没有表现出同步化效应；而不同加工方式玉米对瘤胃代谢的影响较大,在发酵参数方面,饲喂蒸汽压片组奶牛瘤胃液氨氮、乙酸浓度及乙丙比显著低于饲喂粉碎玉米组奶牛,总VFA浓度和CH4估测值较饲喂粉碎玉米组奶牛有降低的趋势,但瘤胃pH、丙酸和丁酸浓度差异不显著；在酶活性方面,饲喂蒸汽压片组奶牛瘤胃内容物木聚糖酶活性显著低于饲喂粉碎玉米组,淀粉酶活性也较饲喂粉碎玉米组奶牛有降低的趋势,但羧甲基纤维素酶活性差异不显著；在微生物菌群组成方面,蒸汽压片玉米处理组日粮奶牛瘤胃内容物甲烷菌、嗜淀粉瘤胃杆菌数量显著低于粉碎玉米组日粮处理组,而牛链球菌数量显著高于粉碎玉米日粮处理组；不同加工方式豆粕日粮对奶牛各瘤胃发酵参数、微生物酶活及数量没有显著影响。本研究结果说明,增加日粮能量释放速率能够提高瘤胃氨氮利用效率,并通过抑制甲烷菌数量减少甲烷排放。
3、日粮能氮释放同步性对奶牛营养物质消化、代谢及生产性能的影响(试验三)
本试验的目的是找出能够增加微生物蛋白合成效率、提高动物生产性能的最佳能氮同步释放模式并阐明其机理。试验设计同试验二。在采样期采集奶样、饲料样、粪样、尿样、血样。结果发现,不同能氮同步释放日粮仅在MUN和BUN浓度方面表现出了同步化效应,但对其他营养物质消化、氮代谢及生产性能参数没有影响；不同加工方式玉米日粮对奶牛影响比较大。在生产性能方面,与饲喂含粉碎玉米日粮奶牛相比,饲喂含蒸汽压片玉米日粮奶牛DMI降低,但产奶量不受影响,从而导致饲喂蒸汽压片玉米组奶牛饲料转化效率显著提高。乳蛋白、乳脂肪及乳糖产量均不受玉米类型的影响;蒸汽压片玉米组日粮奶牛淀粉全肠道表观消化率显著高于粉碎玉米组,但对其他营养成分表观消化率没有影响；与饲喂粉碎玉米组奶牛相比,饲喂蒸汽压片玉米组奶牛氮利用效率(乳氮排出量/总氮摄入量)显著增加,尿中尿素含量及粪氮排出量都有降低的趋势；与饲喂粉碎玉米组奶牛相比,饲喂蒸汽压片组奶牛血清胰岛素含量有升高的趋势,血浆尿素氮浓度显著降低,但对其他血液各生化指标没有显著影响；不同加工方式豆粕仅对部分参数存在影响,与浸提豆粕日粮组相比,热处理豆粕组奶牛微生物蛋白合成量显著降低。本试验结果表明,提高日粮能量释放速率能够提高饲料转化率及氮利用效率。
综上所述,瘤胃导管(OST)取瘤胃液技术的优化,为奶牛瘤胃代谢研究提供了有效的技术手段；日粮能氮同步调控对泌乳中期奶牛瘤胃发酵、微生物蛋白合成及生产性能方面没有表现出预期的同步化效应；相较于蛋白质降解速率,日粮能量降解速率对于奶牛瘤胃代谢及生产性能的影响更大,表明适当增加日粮能量降解速率,可以提高饲料转化效率,减少环境污染。
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.
引文
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