Wageningen Livestock Research, Wageningen University & Research, PO Box 338, 6700 AH, Wageningen, the Netherlands.
Animal Nutrition Group, Wageningen University & Research, PO Box 338, 6700 AH, Wageningen, the Netherlands.
J Dairy Sci. 2021 Dec;104(12):12520-12539. doi: 10.3168/jds.2021-20323. Epub 2021 Sep 3.
The objectives of this study were to induce hindgut and metabolic acidosis via abomasal infusion of corn starch and β-hydroxybutyrate (BHB), respectively, and to determine the effects of these physiological states in early-lactation dairy cows. In a 6 × 6 Latin square design, 6 rumen-fistulated Holstein-Friesian dairy cows (66 ± 18 d in milk) were subjected to 5 d of continuous abomasal infusion treatments followed by 2 d of rest. The abomasal infusion treatments followed a 3 × 2 factorial design, with 3 levels of corn starch and 2 levels of BHB. The infusions were water as control, 1.5 kg of corn starch/d, 3.0 kg of corn starch/d, 8.0 mol BHB/d, 1.5 kg of corn starch/d + 8.0 mol BHB/d, or 3.0 kg of corn starch/d + 8.0 mol BHB/d. A total mixed ration consisting of 35.0% grass silage, 37.4% corn silage, and 27.6% concentrate (on a dry matter basis) was fed at 90% of ad libitum intake of individual cows. The experiment was conducted in climate respiration chambers to facilitate determination of energy and N balance. Fecal pH decreased with each level of corn starch infused into the abomasum and was 6.49, 6.00, and 5.15 with 0.0, 1.5, and 3.0 kg of corn starch/d, respectively, suggesting that hindgut acidosis was induced with corn starch infusion. No systemic inflammatory response was observed and the permeability of the intestine or hindgut epithelium was not affected by the more acidic conditions. This induced hindgut acidosis was associated with decreased digestibility of nutrients, except for crude fat and NDF, which were not affected. Induced hindgut acidosis did not affect milk production and composition and energy balance, but increased milk N efficiency. Abomasal infusion of BHB resulted in a compensated metabolic acidosis, which was characterized by a clear disturbance of acid-base status (i.e., decreased blood total CO, HCO, and base excess, and a tendency for decreased urinary pH), whereas blood pH remained within a physiologically normal range. Abomasal infusion of BHB resulted in increased concentrations of BHB in milk and plasma, but both remained well below the critical threshold values for subclinical ketosis. Induced compensated metabolic acidosis, as a result of abomasally infused BHB, increased energy retained as body fat, did not affect milk production and composition or inflammatory response, but increased intestinal permeability.
本研究的目的是通过瘤胃灌注玉米淀粉和β-羟丁酸（BHB）分别诱导后肠和代谢性酸中毒，并确定这些生理状态对泌乳早期奶牛的影响。采用 6×6 拉丁方设计，对 6 头荷斯坦-弗里生奶牛（泌乳 66±18 天）进行 5 天连续瘤胃灌注处理，随后进行 2 天休息。瘤胃灌注处理采用 3×2 析因设计，有 3 个玉米淀粉水平和 2 个 BHB 水平。灌注处理分别为水（对照）、1.5kg/d 玉米淀粉、3.0kg/d 玉米淀粉、8.0mol/d BHB、1.5kg/d 玉米淀粉+8.0mol/d BHB、3.0kg/d 玉米淀粉+8.0mol/d BHB。用 35.0%的草青贮料、37.4%的玉米青贮料和 27.6%的精料（以干物质为基础）组成的全混合日粮，以个体牛自由采食量的 90%进行饲喂。实验在气候呼吸室中进行，以方便确定能量和氮平衡。随着瘤胃中灌注的玉米淀粉水平的增加，粪便 pH 逐渐降低，分别为 6.49、6.00 和 5.15，0.0、1.5 和 3.0kg/d 玉米淀粉时，表明后肠酸中毒是由玉米淀粉灌注引起的。未观察到全身性炎症反应，肠道或后肠上皮的通透性不受更酸性条件的影响。这种诱导的后肠酸中毒与除粗脂肪和 NDF 外的养分消化率降低有关，这些养分不受影响。诱导的后肠酸中毒不会影响产奶量和组成以及能量平衡，但会提高牛奶氮效率。BHB 瘤胃灌注导致代偿性代谢性酸中毒，其特征为酸碱状态明显紊乱（即血液总 CO2、HCO3-和碱剩余减少，尿液 pH 呈下降趋势），而血液 pH 值仍在生理正常范围内。BHB 瘤胃灌注导致牛奶和血浆中 BHB 浓度增加，但均远低于亚临床酮病的临界阈值。由于 BHB 瘤胃灌注导致的代偿性代谢性酸中毒增加了体脂肪的能量保留，不会影响产奶量和组成或炎症反应，但增加了肠道通透性。
