Fibre in Poultry Rations and Its Relationship with Broiler Performance and Gut Health

Fibre is a nutrient that has been largely ignored in feed formulation, not because it is unimportant, but because it is not well known what ‘fibre’ actually stands for. Firstly, the terms used to describe fibre in feed are confusing and the values they represent are inaccurate. For instance, ‘crude fibre’ is a 19th century relic that does not mean much in monogastric animal nutrition. Its continued use in feed formulation perhaps represents the single largest source of inaccuracy in so-called “least cost feed formulation” that relies on the additivity of all nutrients present in a given diet. This is because crude fibre values are highly variable, and miss up to a third of the fibre constituents in key ingredients such as soybean meal. Furthermore, two other terms that came into existence in the 1960s, acid detergent fibre (ADF) and neutral detergent fibre (NDF), refer to the arbitrary extracts of feed constituents that do not represent unique classes of chemically defined molecules, and these values are not used in feed formulation. They are also not accurate; for example, NDF ignores up to a quarter of the true fibre components - mainly soluble hemicellulose and pectic polysaccharides. A further confusion has arisen in recent years from the use of “fibre additives” that come under the term “structural fibre or components”. This particular class of “fibre” consists mainly of NSP and lignin and is used as additives in poultry feed to enhance gut development in birds that have little or no access to a sufficient amount of coarse material in their feed or environment. Examples of such additives are tree fibres, cereal hulls, straws, bagasse, and woody grass that have a reasonable level of coarseness and can stimulate the gizzard first and foremost.

Secondly, the feed industry currently does not have a reliable and applicable fibre database for feed ingredients commonly used in poultry feed formulation. The true fibre content of feed is well represented by the sum of non-starch polysaccharides (NSP) and lignin. However, it is important to highlight that even when some nutritionists have access to NSP values for commonly used feed ingredients, they have difficulty applying them to feed formulation. This is because: a) there is no clear correlation between the levels of crude fibre and NSP, hampering the ability of nutritionists to set a minimum or maximum value in feed formulation; b) the physical properties of fibre, to a significant degree, dictate its nutritional roles in poultry diets. It is not just solubility or viscosity, rather it is the way the NSP are associated with various components of cell walls, i.e., how they are embedded in cell wall architectures. Such information is not readily available; and c) NSP come in various chemical structures, meaning their digestibility naturally differs widely. The chemical structures also influence the nutritional properties of NSP, be it the digestion by the animal consuming them, or by feed additives such as exogenous enzymes targeting them.

Thirdly, nutritionists need to have the awareness that the use of crude fibre in feed formulation must be phased out because it is not accurate, nor is the representation of true fibre contents in feed ingredients. To achieve this goal, the development of NSP database may initially focus on the total, insoluble and soluble NSP and their relationship with the crude fibre levels used in commercial diets, followed by techniques that enable rapid determination of these fractions. Then, concerted efforts should be directed to producing a database that provides not just NSP values but also physiochemical and nutritional characteristics. For instance, the chemical structures of the entities making up each fraction will be essential for determining the susceptibility of each entity to the digestive process of the animal as well as to exogenous enzymes. This in-depth understanding of the physical and chemical characteristics of NSP will inform future nutritional strategies that target specific fractions and types of fibre in ingredients, to produce desired nutritional and health outcomes in pigs and poultry.