Li Yantao, Lin Xueyan, Liu Chen, Hu Zhiyong, Hou Qiuling, Wang Zhonghua
Ruminant Nutrition and Physiology Laboratory, College of Animal Science and Technology, Shandong Agricultural University, Taian, China.
Front Vet Sci. 2022 Jun 17;9:929587. doi: 10.3389/fvets.2022.929587. eCollection 2022.
To investigate the responses of amino acid metabolism in portal-drained viscera (PDV), liver, and mammary glands (MGs) to a graded gradual decrease of post-ruminal Lys supply, four multi-catheterized lactating goats were used in a 4 × 4 Latin square experiment. Goats were fasted for 12 h and then received a 33-h abomasal infusion of an amino acid mixture and glucose. Treatments consisted of a graded decrease of Lys content in the infusate to 100 (complete), 60, 30, or 0% as in casein. Lys-removed infusions decreased the production of milk, milk protein, fat, and lactose linearly and also decreased arterial Lys concentrations linearly ( < 0.05). Net PDV uptake decreased linearly ( < 0.05) with decreasing PDV loss ratio ( < 0.05). Although liver removal of Lys decreased linearly ( < 0.05), the removal ratio relative to portal absorption changed small, which was about 10% in all four treatments. Reduced Lys supply resulted in a linear decrease in the utilization of Lys in the peripheral tissues (except mammary, < 0.05) and the release of more Lys in MGs. Although net mammary uptake of Lys declined linearly ( < 0.05), lactating goats can partially offset the negative effect of decreased circulating Lys concentrations by increasing mammary affinity ( < 0.05) and increasing mammary blood flow ( < 0.05). Graded removal of Lys from the infusate linearly decreased mammary uptake-to-output ratios of Lys ( < 0.05) suggesting that mammary catabolism of Lys decreased. Meanwhile, the treatments linearly increased circulating concentrations of glucagon and linearly decreased prolactin ( < 0.05). In conclusion, the results of the present study indicated that there were several mechanisms used to mitigate a Lys deficiency, including reduced catabolism of Lys in PDV and peripheral tissues (including MGs) and linearly increased mammary blood flow and mammary affinity together with increased mammary uptake and U:O of branched-chain amino acids (BCAA). Given these changes, the decline in milk protein production could be attributed to the combined effect of mass action with Lys and hormonal status.
为研究门静脉引流内脏（PDV）、肝脏和乳腺（MGs）中氨基酸代谢对瘤胃后赖氨酸供应逐步减少的反应，在一项4×4拉丁方实验中使用了四只多导管插入的泌乳山羊。山羊禁食12小时，然后接受33小时的氨基酸混合物和葡萄糖真胃灌注。处理包括将灌注液中赖氨酸含量逐步降低至酪蛋白中的100%（完整）、60%、30%或0%。去除赖氨酸的灌注液使牛奶、乳蛋白、脂肪和乳糖产量呈线性下降，同时也使动脉赖氨酸浓度呈线性下降（P<0.05）。随着PDV损失率的降低，PDV净摄取量呈线性下降（P<0.05）。虽然肝脏对赖氨酸的清除呈线性下降（P<0.05），但相对于门静脉吸收的清除率变化较小，在所有四种处理中约为10%。赖氨酸供应减少导致外周组织（乳腺除外）中赖氨酸利用率呈线性下降（P<0.05），且乳腺中释放的赖氨酸增多。虽然乳腺对赖氨酸的净摄取量呈线性下降（P<0.05），但泌乳山羊可通过增加乳腺亲和力（P<0.05）和增加乳腺血流量（P<0.05）来部分抵消循环赖氨酸浓度降低的负面影响。从灌注液中逐步去除赖氨酸使乳腺赖氨酸摄取与输出比呈线性下降（P<0.05），表明乳腺中赖氨酸分解代谢减少。同时，处理使胰高血糖素循环浓度呈线性增加，使催乳素呈线性下降（P<0.05）。总之，本研究结果表明，存在几种减轻赖氨酸缺乏的机制，包括PDV和外周组织（包括MGs）中赖氨酸分解代谢减少，乳腺血流量和乳腺亲和力呈线性增加，以及乳腺对支链氨基酸（BCAA）的摄取和U:O增加。鉴于这些变化，乳蛋白产量下降可归因于赖氨酸质量作用和激素状态的综合影响。
