Department of Animal Science, Michigan State University, East Lansing 48824-1225.
Department of Animal Science, Michigan State University, East Lansing 48824-1225.
J Dairy Sci. 2018 Jun;101(6):5082-5091. doi: 10.3168/jds.2017-13607. Epub 2018 Mar 7.
Absorbed fuels from the digestion of starch include propionic acid (PA) produced by ruminal fermentation and glucose (GLU) from intestinal digestion, which may be partially metabolized to lactic acid (LA) by intestinal tissues. Our objective was to evaluate the effects of these fuels on dry matter intake (DMI) and feeding behavior of cows in the postpartum period. We hypothesized that these fuels affect feed intake differently and that their effects are related to differences in their hepatic metabolism. Glucose was expected to have little effect on feed intake because little or no GLU is extracted from the blood by the liver. Whereas both LA and PA are anaplerotic and can stimulate oxidation of acetyl CoA in hepatocytes, hepatic extraction of PA is greater than LA, which depends on cytosolic redox state. Continuous isoenergetic infusions (150 kcal of ME/h) of PA, LA, or GLU or no infusion were administered abomasally to 8 ruminally cannulated multiparous Holstein cows (12.4 ± 6.2 d postpartum) in a duplicate 4 × 4 Latin square design experiment, with four 1-d infusion periods, balanced for carry-over effects. Treatment sequences were assigned to cows randomly, and treatments included control (CON, no infusion), PA (0.41 mol/h), LA (0.46 mol/h), and GLU (0.22 mol/h). Solutions containing treatments were infused at 500 mL/h for 22 h/d and provided ∼3.3 Mcal/d. Feeding behavior was recorded by a computerized data acquisition system. Gross energy digestibility of the diet was determined for each cow and used to calculate metabolizable energy intake (MEI) from the diet. Total MEI was calculated as the sum of MEI from the diet plus energy from infusions. Data were analyzed statistically with a mixed model including the fixed effect of treatment and random effects of block and cow within block. Each treatment was compared with CON by contrasts. Compared with CON, PA decreased DMI by 24% (14.3 vs. 18.9 kg/d) and total MEI by 13% (34.8 vs. 40.2 Mcal/d) with a tendency to decrease meal frequency. Lactic acid decreased DMI by 14% (16.3 vs. 18.9 kg/d) compared with CON by decreasing meal size 20% but did not affect MEI. Glucose infusion did not affect DMI or MEI. Treatment effects on DMI and MEI were consistent with their expected effects on hepatic oxidation. Depression of feed intake in diets containing highly fermentable starch is likely because of differences in hepatic metabolism.
被消化的淀粉吸收的燃料包括瘤胃发酵产生的丙酸（PA）和肠道消化产生的葡萄糖（GLU），这些葡萄糖可能部分代谢为肠道组织的乳酸（LA）。我们的目的是评估这些燃料对产后奶牛干物质采食量（DMI）和采食行为的影响。我们假设这些燃料对采食量的影响不同，它们的影响与肝脏代谢的差异有关。预计葡萄糖对采食量影响不大，因为肝脏从血液中提取的 GLU 很少或没有。而 LA 和 PA 都是氨甲酰磷酸的前体，可以刺激肝细胞中乙酰辅酶 A 的氧化，但 PA 对肝脏的提取量大于 LA，这取决于细胞溶质的氧化还原状态。在一个重复的 4×4 拉丁方设计实验中，用 8 头瘤胃瘘管的经产荷斯坦奶牛（产后 12.4±6.2d）进行了连续等能量（150kcal ME/h）的 PA、LA 或 GLU 灌注（150kcal ME/h）或不灌注处理，共进行了 4 个 1d 灌注期，平衡了残留效应。处理顺序随机分配给奶牛，处理包括对照（CON，不灌注）、PA（0.41mol/h）、LA（0.46mol/h）和 GLU（0.22mol/h）。以 500ml/h 的速度灌注含有处理的溶液 22h/d，提供约 3.3 Mcal/d。通过计算机数据采集系统记录采食行为。为每头奶牛测定日粮的总能消化率，并用于计算日粮的可代谢能摄入量（MEI）。总 MEI 计算为日粮 MEI 与灌注能量之和。数据用包含处理固定效应和块和块内奶牛随机效应的混合模型进行统计分析。通过对比处理与 CON 来比较每个处理。与 CON 相比，PA 降低了 24%的 DMI（14.3 与 18.9kg/d）和 13%的总 MEI（34.8 与 40.2 Mcal/d），同时采食频率有降低的趋势。与 CON 相比，LA 通过降低 20%的采食大小降低了 14%的 DMI（16.3 与 18.9kg/d），但不影响 MEI。葡萄糖灌注不影响 DMI 或 MEI。DMI 和 MEI 的处理效应与它们对肝脏氧化的预期效应一致。高发酵淀粉日粮中采食量下降可能是由于肝脏代谢的差异。
