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核心能量来源，但其价格受环境与政治因素双重影响。2016年，干旱将玉米价格推至历史峰值，严重冲击了奶料比，使得精准配制日粮以实现奶牛最优生产性能成为迫切需求。随着生产成本持续攀升，优化营养平衡、通过提升消化率减少营养浪费已成为行业关键议题。

玉米淀粉消化率主要受醇溶蛋白（prolamin）包埋作用，以及直链淀粉（amylose）与支链淀粉（amylopectin）比例的调控。对玉米进行精细化粉碎可破坏醇溶蛋白的包埋结构，从而显著提升淀粉消化率。此外，直链淀粉与支链淀粉的比例同样会影响淀粉消化效率：直链淀粉占比越高，淀粉的消化难度越大。当前学界对营养性饲料添加剂与酶制剂的研究热度，旨在提升反刍动物的营养利用效率。诸如酵母、植物营养素等饲料添加剂，以及Ronozyme® Rumistar这类酶制剂，已在改善奶牛消化性能与整体生产表现方面展现出良好应用前景。Ronozyme® Rumistar作为一种纯淀粉酶制剂，可在不改变瘤胃pH值的前提下，提升玉米淀粉利用率与纤维消化能力。

本研究探究了不同玉米粒径与添加α-淀粉酶（α-amylase）制剂Ronozyme® Rumistar对淀粉消化及奶牛生产性能的影响。试验涵盖了通过体外法与尼龙袋法（in sacco）评估产奶量、粪便淀粉含量、淀粉与中性洗涤纤维（Neutral Detergent Fiber，NDF）消化率，以及瘤胃发酵参数。研究分为两个阶段开展：第一阶段在商业化奶牛场进行，试验组奶牛饲喂经不同粒径粉碎（粗碎、细碎、超微粉碎）的玉米日粮，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，但更小的玉米粒径可提升乳蛋白含量；更精细的粉碎处理可降低粪便中的淀粉残留量，而添加酶制剂则可减少粪便中的蛋白质含量，提示瘤胃发酵效率得到了改善。

第二阶段在比勒陀利亚大学（University of Pretoria）开展，试验采用安装瘤胃瘘管的奶牛，以精准测定淀粉降解率。结果表明，更精细的玉米粉碎处理可提升淀粉消化率，而添加酶制剂可提高全肠道消化率与挥发性脂肪酸（volatile fatty acid）产量。综合来看，本研究表明，添加酶制剂与优化玉米加工精细度可提升反刍动物日粮的淀粉消化效率与营养利用效能，但仍需开展进一步研究以全面阐明上述效应的作用机制。