Managing fiber better in feed formulation – essential for sustainable livestock production

Fiber often receives scant attention in feed formulation. Primarily because the physicochemical effects of fiber in the gastrointestinal tract are poorly understood and secondly due to an absence of accurate data on the real fiber content, composition and variation in feed ingredients. However this is no longer an option for nutritionists, who must embrace a wider range of higher fiber by-products associated with the consumers’ desire for more sustainable feeds. In this first article we will explore how improved fiber management fits with the quest for more sustainable animal feed production.

The World Resources Institute predicts that to meet the needs of a world population of 9.7 billion, animal protein consumption will reach 445 million tons in 2050. In line with new figures from FAO this means approximately 70% growth compared with today. Consequently, this places the livestock industry under a spotlight, making it a target for criticism, with many questioning how these growth targets can be achieved in a sustainable way. Concurrently, consumers have become more interested in where and how food is produced. Considering the ever shrinking land we have remaining for agricultural expansion and increased consumer demand, using available resources as efficiently as possible will be essential in the future. Similarly, embracing more food and biofuel industry by-products and sourcing more locally will ultimately be key to producing the extra tons of animal protein required.

Animal feeds are changing

With increasing consumer and government pressure to be sustainable, animal nutritionists are increasingly compelled to include a wider range of often more variable ingredients than in the past. This may result in monogastric diet composition changes, which if not appropriately managed could negatively affect animal performance. Specifically, more by-products need to be included to increase global food security and availability but also for economic reasons. There is a shift away from soybean meal to more locally grown protein sources which are perceived to be more sustainable These are often associated with higher fiber content (Figure 1) and contain different fiber profiles, so it is essential to understand their relative contribution and impact.

In recent years there has also been renewed interest in the role of fiber in nutrition, particularly regarding its role in gut health, where moderate levels of certain fiber rich ingredients have been shown to be beneficial. To guide such use as precisely as possible however, requires a deeper understanding of individual fibers and their physiological effects.

Conventional ingredients such as wheat, corn and soybean meal are also under scrutiny. Although typically lower in fiber, they can still exhibit marked variation due to differences in genetics, climate, harvest year and processing conditions (Figure 2). This variation is not always well quantified, and if not well managed can have negative consequences on efficiency and uniformity of animal production.

Figure 1: More sustainable feed raw materials typically increase fiber in monogastric diets

Fibers are not all the same

Historically, dietary fiber has been considered an antinutritional factor, due to its adverse effects on feed intake and nutrient digestibility. Soluble fibers such as beta-glucan from barley and oats, arabinoxylan from wheat and rye or pectin from sugar beet can increase viscosity and decrease passage rate particularly in young poultry and pigs. This in turn reduces feed intake, the rate of nutrient uptake and may impact growth performance. In contrast, strategic use of moderate levels of insoluble fibers found in ingredients such as oat hulls, sunflower hulls, rapeseed meal and sunflower meals have been shown to have a range of positive physiological effects. For example, in poultry diets they may increase chyme retention time in the upper part of the gastro-intestinal tract. This stimulates both gizzard development and endogenous enzyme production, resulting in improvements in digestibility of starch, lipids and other dietary components. Fiber can also help maintain the integrity of small and large intestines by strengthening mucosal structure and function. It can also modulate beneficial microbiota in the large intestine. While dietary fibers cannot be hydrolyzed by the digestive enzymes in the small intestine, they can be somewhat fermented by microflora in the gastro-intestinal tract. The end products include various gases, lactic acid and short chain fatty acids, providing positive benefits for gut health.

These positive effects are, however, very dependent on the level and type of fiber, therefore, a detailed insight into the source, type, form and inclusion level of dietary fiber is critical in order to achieve optimal performance and economic benefits under commercial conditions.

Time to get more accurate

Although there are clear benefits linked to managing fiber better, the approach in feed formulation has evolved little over the last 30 years, where in many cases crude fiber is still used. Developed in 1865, this methodology measures the residue of plant-based food remaining after extraction with solvent, dilute acid and dilute alkali. However, this measurement is somewhat meaningless for monogastric animal nutrition, failing to describe real fiber content in terms of level, composition or physicochemical properties. Furthermore, it underestimates the importance of fiber in feed (Figure 3) and fails to give the insights needed to take advantage of any benefits fiber can bring. For these reasons, it may represent the largest source of error in modern day feed formulation. Two other terms from the 1960’s - acid detergent fiber (ADF) and neutral detergent fiber (NDF) also refer to arbitrary extracts of feed constituents, both ignoring a significant fraction of the total dietary fiber.

A more relevant set of values, representing the content and functional effects of fiber is needed. A good starting point is to replace crude fiber with total dietary fiber (sum of non-starch polysaccharide + lignin) and to split this into water soluble and insoluble fractions (Figure 4).

Considering individual soluble and insoluble non-starch polysaccharides (NSP) such as arabinoxylan, beta-glucan and pectin, as well as certain ratios of mono-sugars which make up these complex structures can help make more informed nutritional decisions. In addition, inclusion of resistant starch, a fraction of starch that is resistant to amylase degradation in the small intestine but displays fiber like properties can add additional insights. Quantitative knowledge about different fiber structures can also help make more informed and targeted decisions on the choice and dose of NSP degrading enzymes in fiber rich diets.

Figure 4: Measuring soluble, insoluble NSP and lignin gives a more complete picture of dietary fiber

Rapid and reliable fiber determination is key

NSP values are primarily derived from enzymatic chemical procedures such as that of Englyst and Cummings, 1988. This method involves enzymatic removal of starch, followed by hydrolysis of the NSP to the constituent sugars, which are measured by gas chromatography. The sugar composition can be used to predict the characteristics of dietary fiber. Whilst information tables of this type exist, they are typically dated and based on relatively few replicates. Composition analysis is time consuming, costly and not suited to routine analysis. Fortunately, the recent development of accurate NIR calibrations for measuring different fiber fractions more precisely can improve the situation immeasurably.

Managing fiber better – essential for sustainable livestock production

In conclusion, feed formulators need to move away from using crude fiber to more accurate and precise measurements of dietary fiber. This is essential if fiber rich ingredients, typical of many locally sourced by-products are to be managed without negative effects on performance efficiency. By taking such steps, nutritionists will also be able to make more strategic use of certain fiber structures for improved health and efficiency as well as managing variation in conventional raw materials better. A more targeted and informed use of NSP degrading enzymes will also be possible. The emerging availability of rapid and reliable NIR based tools for measuring fiber fractions routinely will help spearhead this change in approach.