利用体外产气法和CNCPS法对不同生育期虉草营养价值的评价研究

为了评定不同生育期虉草的营养价值,分析体外产气法和CNCPS法两种营养评价方法的相关性。采用体外产气法测定抽穗期、开花期、灌浆期、乳熟期4个生育期虉草的体外发酵产气量、发酵参数(a、b、c)、DM消化率、NDF和ADF降解率,用康奈尔净碳水化合物和蛋白质体系(cornell net carbohydrate and protein system,CNCPS)分析方法测定相应组分,评价其营养价值,并比较研究两种方法评价结果的相关性。结果表明,体外发酵至72 h结束,累计总产气量和产气参数a以开花期最高(122.68 和4.46 mL),显著高于各组(P<0.05),且从抽穗期、灌浆期、乳熟期有降低的趋势;抽穗期和开花期的DM消化率、NDF和ADF降解率分别显著高于灌浆期和乳熟期(P<0.05)。随着虉草生育期的延长,CP和SOLP呈递减趋势,即抽穗期和开花期显著高于灌浆期和乳熟期(P<0.05);NDF、ADF和ADL呈递增趋势,但NDFIP、ADFIP呈递减趋势。灌浆期和乳熟期的CHO含量显著高于抽穗期和开花期(P<0.05),而CA和CNSC含量则相反,且CC含量同样以灌浆期与乳熟期较高;蛋白质组分中,PA与CA及CC与PC组分呈现同样的趋势。虉草CNSC、CA、CB₁、CB₂、PA、PB₃组分含量与不同时间点产气量呈显著或极显著的相关性(P<0.05或P<0.01)。因此,开花期虉草营养价值最高,其次为抽穗期、灌浆期和乳熟期,产气法和CNCPS评价牧草具有相关性,用体外产气量估测牧草CNCPS组分是可行的。

The nutritional value of reed canary grass at different growth stages,as determined by in vitro gas production and Cornell net carbohydrate and protein system methods

The objective of this study was to evaluate the nutritional value of reed canary grass at different growth stages using in vitro gas production and the Cornell net carbohydrate and protein system (CNCPS) methods,and to compare results from these two methods.The in vitro gas production method was used to de-termine gas production,fermentation parameters (a,b,c),dry matter (DM)digestibility,and the degrada-tion rates of neutral detergent fiber (NDF)and acid detergent fiber (ADF)at heading,flowering,seed filling and milk ripe growth stages of reed canary grass.CNCPS components were also determined for comparison of the two methods.The cumulative total gas production and the a value (122.68 and 4.46 mL)at the flowering stage were significantly higher than those at other stages,and they tended to decrease from the heading to milk ripe stages.Similarly,DM digestibility and degradation rates of NDF and ADF at the heading and flowering stages were significantly higher than those at the seed filling and milk ripe stages.As reed canary grass ma-tured,the crude protein (CP)and soluble protein (SOLP)contents tended to decrease,and were significantly lower at the seed filling and milk ripe stages than at the heading and flowering stages NDF,ADF and acid de-tergent lignin (ADL)components increased while the NDF insoluble protein (NDFIP)and ADF insoluble pro-tein (ADFIP)generally decreased.The carbohydrate (CHO)content at the filling and milk ripe stages was sig-nificantly higher than that at the heading and flowering stages,while sugar content in CHO (CA)and non-structural carbohydrate (CNSC)contents were higher at the heading and flowering stages.The unavailable fi-ber (CC)content was also higher at the milk ripe stage.The protein component,the non-protein nitrogen (PA),and the bound protein (PC)showed similar trends to those of CA and CC.The levels of CNSC,CA, starch+non-starch polysaccharide fractions (CB1 ),CB2 ,PA,and low degradability protein (PB3 )levels of reed canary grass were significantly or very significantly correlated with the gas production at different time points.Therefore,the nutritional value of reed canary grass was the highest at the flowering stage,followed by the heading stage,filling stage and milk ripe stage in that order.The results from the two evaluation meth-ods,in vitro gas production and the CNCPS method,were closely correlated,suggesting that it was feasible to estimate CNCPS components of forages using the in vitro gas production method.