Department of Animal Sciences, University of Lavras, Lavras, MG 37200-000, Brazil; Department of Animal Sciences, University of Florida, Gainesville 32611.
Department of Animal Sciences, University of Lavras, Lavras, MG 37200-000, Brazil.
J Dairy Sci. 2018 Oct;101(10):9052-9057. doi: 10.3168/jds.2018-14870. Epub 2018 Aug 9.
The objectives of this study were to determine (1) the effect of grinding size (1, 2, 4, and 6 mm) to determine effective ruminal disappearance (ERD); (2) the most adequate method to estimate the rapidly degradable fraction (A); (3) a time point to measure the indigestible fraction (C); and (4) the viability of using fewer time points to estimate starch fractional disappearance rate (k) of mature corn grain. Fraction A was determined by rinsing in a bucket or washing machine, rumen immersion followed by bucket or washing machine, and water immersion for 30 min followed by bucket or washing machine. Ruminal in situ incubations were performed at 48, 72, 96, and 120 h to determine fraction C, and at 0 (washing machine), 3, 6, 12, 18, 24, and 48 h to determine the kinetics of starch disappearance. Models were used with either 2 or 3 pools and k was determined by the linear slope of the log-transformed bag residues as a proportion of incubated samples over time. The ERD was calculated as A + B [k/(k + kp)], where kp is the ruminal fractional passage rate = 16.0% h. Data were analyzed using PROC MIXED of SAS (SAS Institute Inc., Cary, NC) with the fixed effects of run (for fraction A analysis only) method (either washing or model), grinding size, and method by grinding size interaction, with cow as a random effect. Correlation between estimates calculated using all time points or combinations of 2 and 3 time points were determined using PROC CORR. Fraction A was reduced as grinding size increased, but was not altered by washing method. Samples ground at 6 mm had greater fraction C than other grinding sizes at 48, 72, or 96 h, but not at 120 h. Model affected the slowly degradable fraction (B) values solely, but the difference was minor (0.5 percentage units). Greater fractions B and C but reduced k and ERD were observed as grinding size increased. Based on correlation analysis the 2-pool model, incubation times of 0, 3, and 48 h were suitable to evaluate ruminal starch degradation kinetics in mature corn. Ruminal in situ incubation at 120 h highlighted the lack of a fraction C of starch (0.13% of starch). Washing method did not affect determination of fraction A of starch. Ruminal in situ incubations of 0, 3, and 48 h for starch degradation kinetics using a 2-pool model were adequate for mature ground corn, but 120 h of incubation is suggested to confirm the existence or absence of a fraction C. Grinding size affected starch degradation kinetics and fraction A determination.
（1）磨碎大小（1、2、4 和 6 毫米）对确定有效瘤胃消失率（ERD）的影响；（2）估计快速降解部分（A）最适当的方法；（3）测量不可消化部分（C）的时间点；以及（4）使用更少的时间点来估计成熟玉米颗粒淀粉分数消失率（k）的可行性。部分 A 是通过在桶或洗衣机中冲洗、瘤胃浸泡后在桶或洗衣机中冲洗、以及 30 分钟水浸后在桶或洗衣机中冲洗来确定的。在 48、72、96 和 120 小时进行瘤胃原位孵育以确定部分 C，并在 0（洗衣机）、3、6、12、18、24 和 48 小时确定淀粉消失动力学。使用具有 2 或 3 个池的模型，并且 k 通过在一段时间内作为孵育样品的比例的对数转换袋残渣的线性斜率来确定。ERD 计算为 A + B [k/（k + kp）]，其中 kp 是瘤胃分数通过速率= 16.0% h。使用 SAS（SAS Institute Inc.，Cary，NC）的 PROC MIXED 对数据进行分析，固定效果为运行（仅用于部分 A 分析）方法（冲洗或模型）、磨碎尺寸和方法与磨碎尺寸的交互作用，以牛作为随机效应。使用 PROC CORR 确定使用所有时间点或 2 和 3 个时间点组合计算的估计值之间的相关性。随着研磨尺寸的增加，部分 A 减少，但冲洗方法不改变。在 48、72 或 96 小时，但是在 120 小时，6 毫米研磨的样品具有比其他研磨尺寸更大的部分 C。模型仅单独影响缓慢降解部分（B）的值，但差异很小（0.5 个百分点）。随着研磨尺寸的增加，观察到更大的部分 B 和 C，但降低了 k 和 ERD。基于相关性分析，2 池模型，0、3 和 48 小时的孵育时间适用于评估成熟玉米的瘤胃淀粉降解动力学。在 120 小时的瘤胃原位孵育突出了淀粉的 C 部分（淀粉的 0.13%）的缺乏。冲洗方法不影响淀粉部分 A 的测定。使用 2 池模型进行淀粉降解动力学的 0、3 和 48 小时瘤胃原位孵育适用于成熟的地面玉米，但建议孵育 120 小时以确认 C 部分的存在或不存在。研磨尺寸影响淀粉降解动力学和部分 A 的测定。
