Analysis of starch digestibility in different particle size maize, effects of amylase enzyme and production parameters in dairy cows

In South Africa, maize is a key energy source for ruminant diets, but its price is influenced by environmental and political factors. In 2016, droughts drove maize prices to record highs, severely impacting the milk-to-feed price ratio and necessitating precise diet formulation for optimal dairy production. As production costs rise, optimizing nutrient balance and reducing nutrient wastage through improved digestibility is crucial.
Maize starch digestibility is primarily affected by prolamin protein encapsulation and the amylose-to-amylopectin ratio. Finer grinding of maize improves starch digestibility by damaging prolamin encapsulation. Additionally, starch digestibility is influenced by the amylose-to-amylopectin ratio, with higher amylose making digestion more challenging. Recent interest in nutrient feed additives and enzymes aims to enhance nutrient efficiency in ruminants. Feed additives like yeast and phytonutrients, and enzymes such as Ronozyme® Rumistar, have shown promise in improving digestion and overall performance in dairy cattle. Ronozyme® Rumistar, a pure amylase, enhances maize starch utilization and fiber digestion without affecting rumen pH.
This study explored how different maize particle sizes and the addition of the α-amylase enzyme Ronozyme® Rumistar affect starch digestion and dairy performance. It included evaluating milk production, faecal starch content, starch and NDF digestion through in vitro and in sacco methods, and rumen fermentation parameters. The research was conducted in two phases. Phase one took place on a commercial dairy farm and involved feeding cows diets with maize ground to different particle sizes (coarse, fine, and micro-milled) with or without the amylase enzyme. Results showed no significant impact on milk yield or fat, but smaller maize particles increased milk protein content. Finer maize reduced starch in manure, and enzyme supplementation decreased manure protein content, suggesting improved rumen fermentation.
Phase two, conducted at the University of Pretoria, involved rumen cannulated cows to measure starch degradability. The results indicated that finer maize particles improved digestibility, and enzyme addition enhanced total tract digestibility and volatile fatty acid production. Overall, the study suggests that enzyme supplementation and finer maize processing can improve starch digestion and nutrient efficiency in ruminant diets, though further research is needed to fully understand these effects.

在南非，玉米是反刍动物日粮的关键能量来源，但其价格受环境与政治因素影响。2016年，干旱推动玉米价格创下历史新高，严重影响了奶料比价，并要求精准日粮配制以实现最优乳品生产。随着生产成本攀升，通过提升消化率优化营养平衡、减少营养浪费至关重要。
玉米淀粉消化率主要受醇溶蛋白（prolamin）包被以及直链淀粉与支链淀粉比值的影响。对玉米进行更精细的粉碎，可通过破坏醇溶蛋白包被提升淀粉消化率。此外，淀粉消化率亦受直链淀粉与支链淀粉比值的影响，直链淀粉占比越高，消化难度越大。
近年来，学界对营养性饲料添加剂与酶制剂的关注聚焦于提升反刍动物的营养利用效率。酵母、植物营养素等饲料添加剂，以及Ronozyme® Rumistar这类酶制剂，已被证实可改善奶牛的消化功能与整体生产性能。Ronozyme® Rumistar作为纯淀粉酶，可在不影响瘤胃pH值的前提下提升玉米淀粉利用效率与纤维消化率。
本研究探究了不同玉米颗粒粒径与添加α-淀粉酶制剂Ronozyme® Rumistar对淀粉消化及乳品生产性能的影响。研究内容包括通过体外法（in vitro）与尼龙袋法（in sacco）评估产奶量、粪便淀粉含量、淀粉与中性洗涤纤维（NDF）的消化率，以及瘤胃发酵参数。本研究分为两个阶段开展。
第一阶段在商业化奶牛养殖场开展，试验组奶牛饲喂采用不同粒径（粗粉碎、细粉碎及超微粉碎）的玉米配制的日粮，分别添加或不添加淀粉酶制剂。结果显示，玉米粒径对产奶量及乳脂率无显著影响，但更小的玉米颗粒可提升乳蛋白含量；更精细的粉碎处理可降低粪便中的淀粉含量，而添加酶制剂则可降低粪便中的蛋白质含量，提示瘤胃发酵功能得到改善。
第二阶段在比勒陀利亚大学开展，试验采用瘤胃瘘管奶牛以测定淀粉降解率。结果表明，更精细的玉米粉碎处理可提升消化率，添加酶制剂则可提升全消化道消化率与挥发性脂肪酸生成量。综合来看，本研究表明，添加酶制剂与优化玉米粉碎工艺可提升反刍动物日粮的淀粉消化率与营养利用效率，但仍需开展进一步研究以全面阐明上述效应的作用机制。