高精料对泌乳期山羊肝脏氨基酸分配与重分配及乳蛋白的影响

为了探讨饲喂不同精粗比日粮对肝脏氨基酸分配与重分配的影响及可能的机制,本研究选择6只安装了肝脏多血管瘘的健康泌乳奶山羊,分别饲喂精粗比为40∶60(对照组)和60∶40(高精料组)的饲料,2×2拉丁方设计,饲喂期16周。期间取乳样,测定乳蛋白含量,并通过肝门静脉、肝静脉和股动脉血管瘘取血, RP-HPLC法测定血浆中游离氨基酸含量。结果表明,高精料组山羊乳中乳蛋白含量显著低于低精料组(P<0.05);肝门静脉血液中各游离氨基酸含量均高于低精料组,而肝静脉和股动脉血液中各游离氨基酸含量均低于低精料组,即高精料组各游离氨基酸在肝脏中的消耗量均多于低精料组,通过股动脉进入乳腺组织的氨基酸含量也少于低精料组。本研究结果显示,长期饲喂高精料日粮,乳蛋白含量降低。其机制与肝脏中氨基酸分配与重分配发生改变,氨基酸在肝脏中消耗量增大,进入乳腺组织合成乳蛋白的前体物氨基酸减少有关。

Effect of a high-concentrate diet on the distribution and redistribution of amino acids in liver and on milk protein of lactating goats

This study explored the effects and probable mechanisms of distribution and redistribution of amino acids in liver of lactating goats fed with different concentrates of forage diet. Six lactating goats fitted with hepatic vascular fistulas were used and they were randomly divided into two groups, in a 2×2 Latin square experiment design with different concentrates to forage ratios of 40∶60 (the control group) and 60∶40 (the high-concentrate group). The experimental interval was 16 weeks. Milk samples were collected and assayed by measuring milk protein content, and plasma samples, including hepatic portal vein, hepatic vein and femoral artery. They were collected via the hepatic vascular fistulas and the contents of free amino acids in plasma were analysed by RP-HPLC. The milk protein content in the high-concentrate group was significantly (P<0.05) lower than that in the low-concentrate group. However, the hepatic portal vein plasma free amino acids content was higher but the contents of hepatic vein and femoral artery plasma free amino acids were lower in the high-concentrate group compared with the low-concentrate group. Thus in the high-concentrate group, the consumption of free amino acids in the liver was more than that in the low-concentrate group, and the content of available free amino acid which transferred into mammary tissue via the femoral artery was less than that in the low-concentrate group. This indicated that long-time feeding with a high-concentrate diet could reduce the milk protein content. Furthermore, it explained that the mechanism of influencing milk protein synthesis was an alteration in concentrations of available free amino acids associated with distribution and redistribution of amino acids in the liver. The amino acids expended in the liver reduced the contents of the mammary gland available amino acids, which are used to synthesize milk protein.