【技术创新】评价反刍动物日粮养分利用率和能量效率

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评价反刍动物日粮养分利用率和能量效率的营养工具

多种因素影响奶牛和肉牛日粮的消化。瘤胃的主要功能是分解纤维和合成微生物蛋白质。这两种功能都是必不可少的，因为动物利用的大部分能量和蛋白质都来自瘤胃。

良好的瘤胃功能将确保最佳的饲料摄入量和消化，而不良的瘤胃功能会对采食量和整体动物生产性能产生负面影响。合理地制定日粮，了解日粮中各个成分是如何协同工作的，可以帮助保持瘤胃-乃至整个牛群-正常运作。

优化饲料利用率

在集约化奶牛及肉牛养殖中，饲料投入通常是最大的单一成本，占总生产成本的60%。然而，研究表明，饲料投入也是养殖场利用率最低的资源之一。饲料的质量和消化率对饲料转化为牛奶或增重有很大影响。

瘤胃不稳定的主要原因之一是酸中毒(即瘤胃pH值低)，这通常是由于消耗了大量高度可发酵的碳水化合物和缺乏足够的有效纤维来维持健康的瘤胃垫和适当的反刍造成的。当淀粉过多时，挥发性脂肪酸(VFA)会积聚并降低瘤胃的pH值。高脂肪日粮也会阻碍瘤胃微生物消化。

劣质牧草也可能对瘤胃功能产生负面影响，导致纤维消化不良和能量利用率降低。由于瘤胃酸中毒导致的纤维消化不良会导致饲料摄入量减少，粪便中未消化纤维的数量增加。

评估营养利用率

为了准确评估饲料的能量和养分的可用性，需要可靠和快速的饲料分析。传统的估计消化率的方法侧重于终产物测量，没有提供关于消化率或日粮将如何影响瘤胃功能的信息，这在评估动物可获得的营养素数量时非常重要。

奥特奇人工瘤胃模型是一种体外发酵模型，模拟瘤胃发酵，评估日粮的营养价值和终产物的形成。试验包括用瘤胃液浸泡饲料和模拟瘤胃自然发酵的缓冲系统。奥特奇人工瘤胃模型是养殖业者、营养学家和饲料厂使用的一种分析工具，用于筛选单独的配料、制定日粮，并就饲料质量或总混合日粮(TMR)做出明智的决定。全混合日粮或全价料的评估是必要的，因为它非常接近模拟动物饲养，并评估日粮中各成分的联合效果。

营养学家传统上依靠营养模型和饲料化学特性来制定奶牛和肉牛的日粮。许多营养服务提供化学成分和消化率的测量，但这些信息是静态的，不能提供对营养可获得性的完整评估。奥特奇人工瘤胃模型是一种更动态的诊断工具，除了估计瘤胃发酵的其他重要终产物外，它还可以估计饲料消化动力学，而不是简单地提供消化率的终点测量。

微生物活性是根据微生物生物量(反刍动物可消化蛋白质的关键来源)和挥发性脂肪酸(VFA)来衡量的，微生物生物量是反刍动物可消化蛋白质的关键来源，VFA是代谢能量的关键来源。奥特奇人工瘤胃模型的目标是为营养学家和生产者提供另一种看待饲料评价的方式，并提出可以补救任何潜在问题的解决方案和策略。通过使用奥特奇人工瘤胃模型，我们可以识别瘤胃发酵的障碍，根据营养可获得性制定日粮，并帮助减少能量损失和饲料浪费。

关键参数和应用

日粮碳水化合物(包括糖、淀粉和纤维)是奥特奇人工瘤胃模型分析的主要焦点，因为它们在瘤胃中被广泛发酵成VFA、气体和微生物生物量。发酵过程中产生的气体可以作为干物质或有机物消化的替代品。气体曲线被拟合到特定的数学模型，以提供关于不同碳水化合物组分的动态和平衡的详细分析。

有两个主要的产气池：一个快速产气池，对应于快速发酵的碳水化合物(主要是糖和有机酸、淀粉和果胶)和一个由不溶性有效纤维或缓慢发酵的碳水化合物组成的慢产气池。

由快速或缓慢降解的碳水化合物提供的能量比例取决于饲料。例如，青贮饲料含有更多的有机酸；谷物含有淀粉；甜菜粕、柑橘渣和大豆皮含有大量果胶单位的能量损失。干草、糖蜜和甜菜粕含有高浓度的糖。瘤胃微生物可利用的养分类型会影响快池和慢池的降解速度，其大小将决定发酵过程中产生的有机酸类型，并可能影响瘤胃微生物的生长速度。

最终的结果将是动物可利用的可消化能量和蛋白质的数量。在日粮中保持粗饲料和精饲料和 (即快速降解碳水化合物)之间的平衡对于最大限度地提高发酵效率至关重要。我们的目标是最大限度地提高微生物生物量和挥发性脂肪酸(VFA)的产量，这是可代谢能量和蛋白质的重要来源，并将被认为造成动物能量损失的发酵气体(如二氧化碳和甲烷)降至最低。

发酵参数和营养概况被用来生成详细的报告，以解决日粮的优点和缺点，并最终提出纠正这些低效的策略。对于养殖场或饲料厂，奥特奇人工瘤胃模型可以帮助解决日粮中的潜在问题、测试养殖场策略、筛选潜在的新产品和/或协助制定日粮。通常，通过改变现有饲料的比例来重新制定日粮，就足以解决很多问题。其他时候，为了实现高效消化，可能需要采购其他饲料。

更可持续的奶牛和肉牛养殖

使用奥特奇人工瘤胃模型配制更多瘤胃友好型日粮，不仅有助于生产者减少实物饲料废物，也有助于减少环境污染。典型奶牛场或育肥场大约60%的碳足迹来自肠道排放(即来自瘤胃的甲烷)和总饲料投入。与Alltech E-CO2农场环境评估结合使用，奥特奇人工瘤胃模型是预测农场和饲料特定肠道甲烷排放量的有效工具。通过联合使用这些工具计算的甲烷排放量数据，已被碳信托基金证实位于IPCC第二级农场模型的第三级。一旦一个农场进行了这样的评估并确定了它的碳足迹，减轻这些排放的各种方法就会变得显而易见。例如，甲烷和一氧化二氮的排放可以通过战略性地改善饮食和粪便管理来减少。Alltech E-CO2已经进行了10,000多个农场评估，可以证明环境效率最高的农场往往也是最有利可图的农场。

全球分析

继最近在英国哈珀·亚当斯大学开设奥特奇人工瘤胃模型实验室之后，奥特奇现在世界各地有7个IFM实验室，另一个将于今年晚些时候在拉丁美洲开设。这样的全球实验室分布有助于使所有地区的生产者都能获得这一工具，从而提高了其农场的整体效率。

自2012年以来，奥特奇人工瘤胃实验室已经分析了超过7000个饲料样本。对这些样本的评估证明，反刍动物的日粮之间存在巨大的差异，反映了饲养系统、原料类型和饲料质量的差异。IFM评估可有效识别以极端发酵为特征的样品，这些样品最有可能带来生产挑战。此外，在动物的生命周期阶段、遗传潜力和其他管理和环境因素允许的情况下，根据它们的生产水平对TMR样本进行排序可以帮助得出“理想的”发酵概况，应该能最大限度地提高动物的性能。

做出合理诠释

瘤胃发酵是一个复杂的过程，发酵的最终产物(包括消化饲料、微生物生物量、挥发性脂肪酸和产气量)的产生主要取决于底物的可获得性和微生物生长的效率。在对日粮做出结论和潜在的调整时，重要的是要考虑到每个参数，而不是专注于单一的指标。

现在，奥特奇IFM比以往任何时候都可以在帮助生产商解决主要环境问题、减少农场废物方面发挥重要作用，并最终能够带来更有利可图和可持续的奶牛和肉牛养殖。

Nutritional tool to evaluate nutrient availability and energy efficiency of ruminant diets

Multiple factors impact the digestion of dairy and beef rations. The primary functions of the rumen are to break down fibre and to synthesise microbial protein. Both functions are essential, as much of the energy and protein utilised by the animal come from the rumen.

Good rumen function will ensure optimal feed intake and digestion, while poor rumen function can negatively impact intake and overall animal performance. Properly formulating the ration and understanding how the individual ingredients in the ration work together can help keep the rumen — and the herd in general — functioning properly.

Optimising feed utilisation

In intensive dairy or beef production, feed inputs typically represent the single biggest cost, accounting for up to 60% of total production costs. However, research suggests that feed inputs are also one of the most under-utilised resources on the farm. Efficient conversion of feed into milk or liveweight gain is highly influenced by the quality and digestibility of feeds.

One of the main causes of rumen upset is acidosis (i.e., low rumen pH), often caused by consuming large amounts of highly fermentable carbohydrates and a lack of enough effective fibre to maintain a healthy rumen mat and proper rumination. When there is too much starch, volatile fatty acids (VFA) can build up and reduce the rumen pH. Rations that are high in fat can also impede microbial digestion in the rumen.

Poor-quality forage may also negatively impact rumen function, leading to poor fibre digestion and reduced energy availability. Poor fibre digestion due to ruminal acidosis conditions can lead to reduced feed intake and increased amounts of undigested fibre in the manure.

Evaluating nutrient availability

To accurately assess the availability of energy and nutrients of feeds, reliable and rapid feed analyses are required. Traditional methods of estimating digestibility focus on end-point measurements and do not provide information about the rates of digestion or about how the diet will impact rumen function, which are very important to know when assessing the amount of nutrients available to the animal.

Alltech IFM is an in vitro fermentation model that simulates rumen fermentation and evaluates the nutritive value of a ration and end-product formation. The test consists of incubating feeds with rumen fluid and a buffer system to mimic natural rumen fermentation. Alltech IFM is an analytical tool used by farmers, nutritionists and feed manufacturers to screen individual ingredients, formulate rations and make informed decisions about the quality of feeds or total mixed rations (TMRs). The evaluation of TMRs or complete feeds is advantageous because it closely simulates animal feeding and evaluates the associative effects of ingredients within the ration.

Nutritionists have traditionally relied on nutritional models and feed chemical characteristics to formulate diets for dairy and beef animals. Many nutritional services provide measurements of chemical composition and digestibility, but this information is static and does not provide a complete evaluation of nutrient availability. Alltech IFM is a more dynamic diagnostic tool that estimates the kinetics of feed digestion, in addition to other important end products of rumen fermentation, rather than simply providing an end-point measurement of digestibility.

Microbial activity is measured in terms of microbial biomass, a critical source of digestible protein for ruminants, as well as VFA, a critical source of metabolizable energy. The goal of Alltech IFM is to offer nutritionists and producers another way of looking at feed evaluation and to propose solutions and strategies that could remedy any potential issues. By using Alltech IFM, we can identify barriers to rumen fermentation, formulate rations based on nutrient availability and help reduce energy losses and feed wastage.

Key parameters and applications

Dietary carbohydrates (including sugars, starch and fibre) are the main focus of Alltech IFM analysis, as they are extensively fermented in the rumen into VFA, gases and microbial biomass. The gas produced during fermentation can be used as a proxy for dry or organic matter digestion. The gas curve is fitted to specific mathematical models to provide detailed insights on the dynamics and balance of different carbohydrate fractions. Two major pools are derived: a fast pool that corresponds to rapidly fermented carbohydrates (mainly sugars and organic acids, starch and pectin) and a slow-pool gas production that consists of insoluble available fibre or slowly fermented carbohydrates.

The proportion of energy supplied from quickly or slowly degrading carbohydrates depends on the feedstuff. For example, ensiled feeds contain more organic acids; cereal grains contain starch; and beet pulp, citrus pulp and soy hulls contain significant amoconsidered energy losses unts of pectins. Grass hay, molasses and beet pulp contain large concentrations of sugars. The type of nutrients available to rumen microbes will affect the rate of degradation of the fast and slow pools, and their sizes will determine the type of organic acids produced during fermentation and may affect the growth rates of rumen microbes.

The end result will be variable amounts of digestible energy and protein available to the animal. Maintaining a balance between forages and concentrates (i.e., quickly degrading carbohydrates) among feedstuffs in a ration is critical to maximise the efficiency of the fermentation. The goal is to maximise the production of microbial biomass and VFA, which are important sources of metabolizable energy and protein, and to minimise the fermentation gases (e.g., carbon dioxide and methane) that are considered energy losses for the animal.

Fermentation parameters and nutrient profiles are used to generate detailed reports to address the strengths and weaknesses of rations and, ultimately, to propose strategies to correct these inefficiencies. For a farm or feed manufacturer, Alltech IFM can help troubleshoot potential problems in a ration, test on-farm strategies, screen potential new products and/or assist in formulating rations. Often, reformulating the ration by changing the feeding rates of the existing feedstuffs is sufficient to fix any issues. Other times, sourcing other feeds may be required in order to achieve efficient digestion.

More sustainable dairy and beef production

The use of Alltech IFM to formulate more rumen-friendly diets helps producers reduce not only physical feed waste but environmental waste, too. Around 60% of a typical dairy or beef farm’s carbon footprint is derived from enteric emissions (i.e., methane from the rumen) and total feed inputs. Used together with an Alltech E-CO2 on-farm environmental assessment, Alltech IFM is an effective tool for predicting farm- and feed-specific enteric methane emissions. Data on methane emissions calculated by using these tools together, has been verified by the Carbon Trust to sit within tier 3 of an IPCC tier 2 farm model. Once a farm has undertaken such assessments and has identified its carbon footprint, various ways to mitigate these emissions will become apparent. For instance, methane and nitrous oxide emissions can be reduced by strategically improving diets and manure management. Alltech E-CO2, which has conducted more than 10,000 farm assessments, can testify that the most environmentally efficient farms are often the most profitable farms as well.

Global analysis

Following the recent opening of the Alltech IFM lab at Harper Adams University in the UK, Alltech now has seven IFM labs around the world, with another due to open in Latin America later this year. Such a global presence has helped make this tool accessible to producers in all regions leading to improvements in the overall efficiency of their farms.

Since 2012, more than 7,000 feed samples have been analysed at Alltech IFM labs. The evaluation of these samples has proven that there are vast differences among ruminant diets, reflecting variabilities in feeding systems, types of ingredients and the quality of feeds. Alltech IFM evaluations are effective at identifying samples that feature extreme fermentation, which are most likely to present production challenges. In addition, ranking TMR samples according to their level of production can help derive an “ideal” fermentation profile that should maximise animal performance, provided the animals’ stage of lifecycle, genetic potential and other management and environmental factors are permissive.

Making the right interpretation

Rumen fermentation is a complex process in which the end products of fermentation (including digested feed, microbial biomass, VFA and gas production) are produced in proportions that depend primarily on substrate availability and the efficiency of the microbial growth. It is important to take every parameter into consideration instead of focusing on a single metric when making conclusions about and potential adjustments to a diet.

Now, more than ever before, Alltech IFM can play a significant role in helping producers address major environmental concerns, reduce waste on-farm and, ultimately, can lead to more profitable and sustainable dairy and beef production.

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