School of Animal Sciences, Virginia Tech, Blacksburg, VA 24061, United States.
Department of Animal Science, Aarhus University, Foulum, DK-8830 Tjele, Denmark.
Animal. 2023 May;17(5):100778. doi: 10.1016/j.animal.2023.100778. Epub 2023 Mar 16.
Characterisation of amino acid (AA) use by the ruminal vein-drained viscera (RDV) has not been assessed in vivo in dairy cattle, and thus, the extent of ruminal AA use from arterial and postabsorptive blood supplies is unclear. Understanding the complete use of AA by the splanchnic bed may lead to alternative feeding programmes that maximise animal N efficiency. The objective of this work was to determine how different nutritional manipulations affect RDV net appearance and apparent affinity for arterial AA in lactating dairy cattle. Data from two arterio-venous (A-V) difference studies, that used a common set of multicatheterised lactating Holstein cows, assigned to different nutritional treatments, were used to assess ruminal metabolism. Study 1 consisted of three dietary treatments at calving [an alfalfa-glucogenic diet, a glucogenic diet (GLCG), or a ketogenic diet (KETO)] to investigate the effects of dietary nutrients and increasing intake postpartum on RDV metabolism of AA at -14, +4, +15, and +29 days relative to calving (DRTC). Study 2 consisted of two dietary levels of CP (17 or 13%) and three ruminal buffers (ammonia, butyrate, and control) to investigate the level of dietary CP and ruminal fermentation products on RDV metabolism of AA. Blood was collected at 9, 20, and 30 min after buffer administration. Regardless of dietary nutrients or fermentation products present in ruminal fluid, net RDV uptake was positive for most AA, excepting Asp, Cys, Glu, and Ser, which were consistently negative. The general positive net uptakes indicate that any AA potentially absorbed from the rumen were not adequate to meet apparent needs. Ruminal plasma flow and net RDV uptake of Trp, Ala, Gly, and Pro increased linearly with increased DRTC. Feeding KETO or GLCG diets increased ruminal plasma flow, and net RDV uptake of Thr and Gly. Feeding high CP diets increased ruminal uptake of Leu, Phe, and Val. The increased AA uptakes were partially driven by increased plasma flow, however, tissue affinity as reflected in clearance rates also increased or tended to for Met, Trp, Ala, Gly, Pro, and Tyr suggesting that changes in RDV uptake were regulated and not due solely to mass action. In conclusion, splanchnic tissue bed responses to dietary and washed rumen conditions were in part driven by changes in RDV nutrient demand and metabolic activity. The adaptive responses alter the fraction of absorbed AA utilised for non-productive purposes and thus the efficiency of conversion of those AA to product.
瘤胃静脉引流脏器（RDV）对氨基酸（AA）的利用特性尚未在奶牛体内进行评估，因此，尚不清楚来自动脉和吸收后血液供应的瘤胃 AA 利用程度。了解内脏器官对 AA 的完整利用情况可能会导致采用最大化动物氮效率的替代饲养方案。本工作的目的是确定不同的营养处理如何影响泌乳奶牛的 RDV 净出现和对动脉 AA 的表观亲和力。使用一组常见的多导管化泌乳荷斯坦奶牛，分配到不同的营养处理，来自两项动静脉（A-V）差异研究的数据用于评估瘤胃代谢。研究 1 在分娩时包括三种饲粮处理[苜蓿-生糖饲粮、生糖饲粮（GLCG）或生酮饲粮（KETO）]，以研究饲粮营养物和产后摄入增加对 -14、+4、+15 和+29 天相对分娩日（DRTC）时 RDV 代谢 AA 的影响。研究 2 包括两种 CP 水平（17 或 13%）和三种瘤胃液缓冲剂（氨、丁酸盐和对照），以研究饲粮 CP 水平和瘤胃发酵产物对 RDV 代谢 AA 的影响。缓冲剂给药后 9、20 和 30 分钟采集血液。无论瘤胃液中存在何种饲粮营养物或发酵产物，大多数 AA 的 RDV 净摄取均为正值，除 Asp、Cys、Glu 和 Ser 外，这些 AA 的 RDV 净摄取均为负值。总的净摄取呈正表明，从瘤胃中吸收的任何 AA 都不足以满足表观需求。随着 DRTC 的增加，Trp、Ala、Gly 和 Pro 的 RDV 净摄取和瘤胃血浆流量呈线性增加。饲喂 KETO 或 GLCG 饲粮增加了 Thr 和 Gly 的瘤胃血浆流量和 RDV 净摄取。饲喂高蛋白饲粮增加了 Leu、Phe 和 Val 的瘤胃摄取。AA 摄取的增加部分是由血浆流量增加驱动的，然而，如清除率所示，组织亲和力也增加或倾向于 Met、Trp、Ala、Gly、Pro 和 Tyr，这表明 RDV 摄取的变化是受到调节的，而不仅仅是由质量作用驱动的。总之，内脏组织床对饲粮和冲洗瘤胃条件的反应部分是由 RDV 营养需求和代谢活性的变化驱动的。适应性反应改变了用于非生产性目的的吸收 AA 部分，从而改变了这些 AA 转化为产物的效率。
