Ylinen Vappu, Pylkkö Päivi, Peura Jussi, Valaja Jarmo
Department of Agricultural Sciences, University of Helsinki, Helsinki, Finland.
Kannus Research Farm Luova Oy, Kannus, Finland.
Arch Anim Nutr. 2020 Jun;74(3):237-255. doi: 10.1080/1745039X.2020.1716655. Epub 2020 Mar 11.
To formulate low-protein diets for blue foxes with sufficient amounts of amino acids (AA), AA digestibility and AA requirements of the animals are crucial information. Therefore, a digestibility and nitrogen (N) balance trial was conducted with 20 blue foxes to determine the macronutrient and AA digestibility and N utilisation in low-protein diets supplemented with DL-methionine (Met) and L-histidine (His). In addition, plasma urea and plasma AA were measured. The diets were designated as P24 (control), P20, P20M, P16M and P16MH and contained energy from digestible crude protein (DCP) at 24%, 20% or 16% of total dietary metabolisable energy (ME). The 20% protein level was fed with or without Met and the 16% protein level was fed with Met and with or without His. The apparent total-tract digestibility (ATTD) of crude protein linearly decreased with decreasing dietary protein level. The ATTD of dry matter, organic matter and crude carbohydrates increased when wheat starch was added as a replacement for protein. The apparent ileal digestibility (AID) and ATTD methods were compared to determine the AA digestibility. The decreasing dietary protein supply decreased the ATTD of most of the AA: threonine, tryptophan (Trp), valine, alanine (Ala), aspartic acid (Asp), glutamic acid, glycine (Gly), proline (Pro), serine (Ser) and total AA. The AID of the AA was constant between diets. Diverging AA showed higher or lower digestibility when determined in the AID or ATTD methods. Isoleucine, lysine, Met, Ala and tyrosine showed higher levels of AID. Arginine, His, cysteine (Cys), Trp, Asp, Gly, Pro and Ser showed higher levels of ATTD, which may reflect the net loss of these AA in the large intestine. Met and His supplementation improved the ATTD and AID of the AA in question, respectively, but did not affect the other variables examined. N retention did not differ between diets and renal N excretion decreased with decreasing protein level; thus N utilisation improved. It was concluded that the protein supply and AA composition in low-protein diets with supplemented Met were adequate for adult blue foxes, since the lower protein supply improved N utilisation and did not affect N retention. However, His supplementation failed to reach the designed level and therefore showed no clear results.
为了配制氨基酸（AA）含量充足的蓝狐低蛋白日粮，动物的AA消化率和AA需求量是关键信息。因此，对20只蓝狐进行了消化率和氮（N）平衡试验，以确定在补充DL-蛋氨酸（Met）和L-组氨酸（His）的低蛋白日粮中常量营养素和AA的消化率以及N的利用率。此外，还测定了血浆尿素和血浆AA。日粮被指定为P24（对照）、P20、P20M、P16M和P16MH，其可消化粗蛋白（DCP）提供的能量分别占日粮总代谢能（ME）的24%、20%或16%。20%蛋白质水平的日粮分别添加或不添加Met，16%蛋白质水平的日粮添加Met且分别添加或不添加His。随着日粮蛋白质水平的降低，粗蛋白的表观全肠道消化率（ATTD）呈线性下降。当用小麦淀粉替代蛋白质时，干物质、有机物和粗碳水化合物的ATTD增加。比较了表观回肠消化率（AID）和ATTD方法来测定AA消化率。日粮蛋白质供应的减少降低了大多数AA的ATTD：苏氨酸、色氨酸（Trp）、缬氨酸、丙氨酸（Ala）、天冬氨酸（Asp）、谷氨酸、甘氨酸（Gly）、脯氨酸（Pro）、丝氨酸（Ser）和总AA。各日粮之间AA的AID保持恒定。不同的AA在AID或ATTD方法测定时显示出较高或较低的消化率。异亮氨酸、赖氨酸、Met、Ala和酪氨酸的AID水平较高。精氨酸、His、半胱氨酸（Cys）、Trp、Asp、Gly、Pro和Ser的ATTD水平较高，这可能反映了这些AA在大肠中的净损失。补充Met和His分别提高了相关AA的ATTD和AID，但未影响所检测的其他变量。各日粮之间N保留无差异，且肾脏N排泄随蛋白质水平的降低而减少；因此N利用率提高。得出的结论是，补充Met的低蛋白日粮中的蛋白质供应和AA组成对成年蓝狐是充足的，因为较低的蛋白质供应提高了N利用率且未影响N保留。然而，His的补充未达到设计水平，因此未显示出明确的结果。
