构树在肉牛瘤胃中降解特性的研究

Ruminal degradation characteristics of Broussonetia papyrifera in beef cattle

为使构树能够作为非常规饲料用于反刍动物养殖生产中,以3头安装有永久瘘管的24月龄安格斯肉牛为试验动物来探究构树在瘤胃中的降解特性和营养价值,使用瘤胃尼龙袋法测定构树的叶、去叶枝条、125~135 cm及145~155 cm高全株构树在瘤胃内的降解率和降解参数并计算瘤胃能氮平衡参数。结果表明:1)叶的粗蛋白质(CP)水平高达23.18%,显著高于其他3种形态构树(P<0.05),全株构树的CP含量显著高于去叶枝条(P<0.05),而酸性洗涤纤维(ADF)则呈现相反规律,其中125~135 cm全株ADF含量低于145~155 cm全株(P>0.05);2)叶的干物质(DM)、有机物(OM)、CP和ADF的有效降解率(ED)均显著大于125~135 cm和145~155 cm全株(P<0.05),三者又均显著大于去叶枝条(P<0.05),四者DM的ED均在40%以上,叶为65.82%;3)叶的瘤胃降解蛋白(RDP)与过瘤胃蛋白(RUP)之比显著高于其他3种形态构树(P<0.05),说明叶的RDP含量高于RUP含量,而其他3种形态构树RUP含量高于RDP含量;4)叶的瘤胃能氮平衡值(RENB)为负(-22.27 g·kg^-1),去叶枝条、125~135 cm及145~155 cm全株的RENB为正,分别为28.79、30.87和27.74 g·kg^-1。结论:4种形态构树的营养价值依次为叶>125~135 cm全株>145~155 cm全株>去叶枝条。其中,构树叶可作为蛋白质饲料使用,其他3种形态构树可以粗饲料的形式使用,4种形态构树均有成为优质饲料资源的潜力,但是在使用时应注意保持能氮平衡。

In order to evaluate the potential of Broussonetia papyrifera for use in ruminant production as an unconventional feed,three beef cattle aged 24 months,each with a permanent rumen fistula,were used to investigate the degradability characteristics and nutritive value of different plant parts of B.papyrifera.Leaves,leafless branches,and whole plants of B.papyrifera were evaluated with a nylon bag technique,to calculate ruminal energy and nitrogen balance using digestibility and degradation parameters.Tests were carried out for smaller(height 125-135 cm)and larger(height 145-155 cm)plants.It was found that:1)Crude protein(CP)content of the leaves was 23.18%,which was significantly higher than branches or whole plants of B.papyrifera(P<0.05),while the CP contents of the whole plants were significantly higher than that of the leafless branches(P<0.05).As expected,the pattern of results for acid detergent fiber(ADF)was opposite to that for CP.The ADF content of 125-135 cm whole plants was lower than that of 145-155 cm whole plants(P>0.05).2)For leaves,values for effective degradability(ED)of dry matter(DM),organic matter(OM),CP and ADF were significantly higher than for whole plants of either height range(P<0.05).Furthermore,leaves and whole plants of B.papyrifera had higher ED of DM,OM,CP and ADF than leafless branches(P<0.05).The ED of DM of all tested B.papyrifera materials was above 40%,and the ED of leaves was up to 66%.3)The ratio of rumen degradable protein(RDP)to rumen undegradable protein(RUP)of leaves was significantly higher than that of branches or whole plants(P<0.05),indicating that RDP proportion was in leaves.For branches and whole plants,the RDP content was lower than RUP content.4)Rumen energy nitrogen balance value(RENB)of leaves was negative(-22.27 g·kg^-1)while the RENB values of leafless branches(28.79 g·kg^-1),125-135 cm whole plants(30.87 g·kg^-1)and 145-155 cm whole plants(27.74 g·kg^-1)were positive.In conclusion,the ranking for nutritive value of the tested B.papyrifera materials was:leaves>125-135 cm whole plants>145-155 cm whole plants>leafless branches.All of the tested materials have the potential for use in high-quality feeds.Leaves can be used as a dietary protein source,while branches or whole plants can be used as roughage.However,energy and nitrogen balance are practical details also needing to be considered.