黑龙江省主要栽培的禾本科牧草对奶牛的营养价值评价

Nutritive evaluation of common grass forage crop for dairy cattle in Heilongjiang

通过对常见的13种栽培禾本科牧草的常规营养成分测定及用尼龙袋法测定的干物质在瘤胃72 h降解率(RDMD)的测定,结果表明:l)用营养成分和RDMD等指标进行评定,2个冰草Agropyron cristatum品种营养价值最高,猫尾草Phleum pratense次之,3个披碱草Puccinellia tenuiflora品种居中,羊草Leymuschinensis和墨西哥玉米Zea mays较差,谷莠子Setaria anceps和稗草Echinochloa crusgalli最差。2)禾本科牧草RDMD与ADF、ADL含量呈极显著负相关(P<0.05)。利用回归方程可以用ADF、ADL含量来预测禾本科牧草的RDMD。3)应用干物质采食量(DMI)、产奶净能(NEL)估测模型计算了各种禾本科牧草的分级指数(GI)值,并参照豆科和禾本科牧草质量分级标准对研究测定的禾本科牧草等级进行划分,其结果是:符合优质牧草等级的有高冰草、中间冰草,符合中等牧草等级标准的有无芒雀麦Bromus inermis、垂穗披碱草、东北羊草、吉生羊草、百特猫尾草、猎犬披碱草、润宝高丹草Sorghum×Sudan。属于劣质牧草的有粗穗披碱草Elymus dahuricus、墨西哥玉米、稗草、谷莠子。4)用单一的营养指标如化学成分、干物质降解率不能准确地评价牧草的营养价值。只有综合考虑DMI、养分含量、消化率和有效能才能对牧草的营养价值做出正确的评价。使用GI值能明显区分养分含量差异很小的不同种类牧草,这说明分级指数是评价牧草营养价值的最权威指标。

The study was conducted to determine chemical composition and 72 hours dry matter de gradability of 15 variety of common cultivated grass by nylon bag method with objective of evaluating nutritional value of grass for dairy cattle. The results showed： 1） in terms of chemical composition and ruminal dry matter degradability （RDMD）, two wheatgrass （Agropyron cristatum） varieties had the highest nutritional value of all gramineous samples, timothy（Phleum pratense） was the second, three wildryegrasses（Puccinellia tenuiflora ） were medium, northeast wild-rye （Leymus chinensis ） and Mexico corn（Zea nays） were poor, hristlegrass （Setaria anceps） and barnyard grass （Echinochloa crusgalli） were the lowest. 2） There was significantly negative correlation between RDMD and ADF or ADL content in gramineaes（P^0.05）. RDMD of gramineous hay could be predicted by the regres- sion equation in which ADF and ADL contents were independent variables. 3）Grading Index of various grass were estimated by using DMI and NE prediction model. The present research classes these forages into five categories according to GI value as follows; high wheatgrass and median wheatgrass belong to high quality forage, smooth brome（Bromus inermis）, droop-ear wildryegrass, Northeast wild-rye, Jilin wildrye, Baite timothy, Hound wildryegrass and Sorghum × Sudan grass belong to medium quality forage, thick-ear wildryegrass（Elymus dahuricus）, Mexico maize, barnyard grass and bristlegrass belong to low quality forage. 4）It is impossible to precisely evaluate nutritional value of forage using single index（for example, chemical composition, dry matter degradability）. As long as DMI, nutrient content, digestibility and available energy are together taken into account, evaluation of forage with precision is possible. Differentiation of a variety of forage with minor nutrient discrepancy by using GI can indicate that GI is an authoritative index evaluating forage quality.