Five ruminally cannulated steers (body weight = 390 ± 7.86 kg) were used in two experiments to evaluate the effects of flake density and starch retrogradation on in situ ruminal degradation of steam-flaked corn. In experiment 1, sifted flakes with flake densities of 257, 296, 335, 373, and 412 g/L (enzymatic starch availabilities: 87%, 76%, 66%, 43%, and 49%, respectively) were evaluated in a randomized complete block design experiment. In experiment 2, the experimental design was a randomized complete block design with a 3 × 2 factorial arrangement of treatments. Three steam-flaked corn fractions corresponding to different particle sizes were used: flakes + fines (not sifted; >4 and <4 mm), sifted flakes (>4 mm), and sifted fines (<4 mm). Particle size fractions were stored for 3 d at either 23 °C or 55 °C (starch availabilities averaged across particle sizes: 53.3% and 25.5%, respectively) in heat-sealed foil bags. Samples were ruminally incubated for 0, 3, 6, 12, 24, 48, 72, or 96 h. Degradation data were modeled to obtain the rate and extent of degradation and passage rate was set to 6% per hour. In experiment 1, the rate of degradation decreased linearly (P < 0.01) and in situ ruminal dry matter (DM) degradability decreased linearly (P < 0.01) from 78.9% to 57.3% as flake density increased from 257 to 412 g/L. In experiment 2, storage of steam-flaked corn samples at 55 °C for 3 d decreased (P < 0.01) the rate of degradation by 37.6% across all particle sizes. Storing samples at 55 °C for 3 d decreased (P < 0.01) in situ ruminal DM degradability of flakes + fines, sifted flakes, and sifted fines by 20.9%, 22.6%, and 14.7%, respectively. Using data from experiment 1 and 2, enzymatic starch availability of sifted flakes was positively correlated (R2 = 0.97; P < 0.01) with in situ ruminal DM degradability. The results demonstrate that decreased starch availability resulting from either starch retrogradation or increased flake density is associated with decreased ruminal digestibility. Decreases in starch availability and in situ ruminal degradability may indicate that increasing flake density or starch retrogradation could potentially alter the site of digestion in cattle. Using prediction equations, decreases in ruminal starch digestibility of steam-flaked corn caused by increasing flake density or increasing starch retrogradation could increase energetic efficiency, depending on the rate of passage and if small intestinal starch digestibility is maintained.

中文翻译：

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薄片密度和淀粉回生影响蒸汽压片玉米的原位瘤胃降解特性和预测的淀粉消化率和能量效率

在两个实验中使用 5 头瘤胃插管肉牛（体重 = 390 ± 7.86 kg）来评估玉米片密度和淀粉回生对蒸汽压片玉米原位瘤胃降解的影响。在实验 1 中，对片状密度分别为 257、296、335、373 和 412 g/L（酶淀粉利用率：分别为 87%、76%、66%、43% 和 49%）的筛分片进行了评估。随机完全区组设计实验。在实验 2 中，实验设计是具有 3 × 2 因子处理的随机完全区组设计。使用了对应于不同粒度的三种蒸汽压片玉米级分：薄片+细粉(未过筛；＞4和＜4mm)、过筛薄片(＞4mm)和过筛细粉(＜4mm)。将粒度级分在 23 °C 或 55 °C 下储存 3 天（不同粒度的平均淀粉利用率：分别为 53.3% 和 25.5%）在热封箔袋中。将样品在瘤胃中孵育 0、3、6、12、24、48、72 或 96 小时。对降解数据进行建模以获得降解速率和程度，并将通过速率设置为每小时 6%。在实验 1 中，随着薄片密度从 257 增加到 412 g/，降解率线性下降 (P < 0.01)，原位瘤胃干物质 (DM) 可降解性从 78.9% 线性下降到 57.3% (P < 0.01)。 L. 在实验 2 中，蒸汽压片玉米样品在 55°C 下储存 3 天后，所有粒径的降解率降低了 37.6%（P < 0.01）。将样品在 55°C 下储存 3 天减少（P < 0. 01) 薄片+细粉、筛分薄片和筛分细粉的瘤胃干物质原位降解率分别提高了20.9%、22.6%和14.7%。使用来自实验 1 和 2 的数据，过筛薄片的酶促淀粉利用率与瘤胃 DM 原位降解性呈正相关（R2 = 0.97；P < 0.01）。结果表明，淀粉回生或薄片密度增加导致的淀粉利用率降低与瘤胃消化率降低有关。淀粉可用性和原位瘤胃可降解性的降低可能表明增加薄片密度或淀粉回生可能会改变牛的消化部位。使用预测方程，