Benefit of fibre in layer dietsPublished Tuesday, 29th November 2022
Dr. Dimcho Djouvinov and Dr. Xaviere Rousseau, AB Vista, Marlborough, UK
Fibre compound is traditionally assumed to have minimal or diluting effects on dietary nutrients – and even having a potentially antinutrient effect. But newly-developed fibre assays and cumulated data of feed fibre effects give a different view on fibre structure and its role in poultry nutrition, including laying hens.
Because of the impact of fibre on animal performance and gut health, this topic is of great interest, especially considering the long lifecycle of those animals, animal welfare concerns and the higher concentration of fibrous ingredients typically used in laying hen diet formulations.
How is fibre measured?
The assay of crude fibre is easy to perform and is still in use as a declared dietary parameter for poultry feeds in many countries.
However, this method underestimates total dietary fibre content. The neutral detergent (NDF) and acid detergent fibre (ADF) methods (Van Soest, 1963) give better quantification of fibre levels in feeds but analyse all insoluble compounds that are not necessarily fibre.
Chemically, total dietary fibre should be considered as the sum of lignin and non-starch polysaccharides (NSPs), with NSPs representing the main proportion and playing a functional role. The NSP levels and profile in the final feeds for layers are a consequence of optimization constraints, type and inclusion rate of ingredients and their processing and storage.
Formulation of conventional layer diets for peak production phase with wheat, maize and soya could result in total dietary fibre content of around 11% (Table 2).
However, in different commercial situations, depending on geography, market conditions and prices, alternative cereals and protein sources, rich in fibre, are available and might be preferred for usage. These include barley, oats, wheat bran, sunflower meal, rapeseed meal and oat hulls.
Introduction of such ingredients increases total dietary fibre, total NSP and modifies the NSP profile and contents compared to a low fibre diet (Table 2).
Typically, the diluting effect of increasing fibre ingredients requires two approaches, depending on the targeted production goals and effectiveness: maintaining the energy density of the formula by increased addition of oil (High Fibre HF diet) or feeding lower energy diet (HF/low energy diet).
Laying hens are able to compensate the latter type of diets through increased feed intake and maintaining a daily intake of nutrients. This means that the daily intake of fibre per head is increased. Other nutrients can also be adjusted in line with the energy density targeted. But it is necessary to stress that only considering the dilution effect of dietary fibre would be an oversimplification.
Chemical properties and levels of NSPs in feeds should be estimated in relation to their functionality, their effects on digestion and on the intestinal balance.
The use of NSPase typically overcomes the detrimental effect of high inclusion of viscous ingredients and even shows further benefits through the production of prebiotics oligosaccharides. The value of soluble NSPs is clearly underestimated as only their viscosity effect is considered whereas they also have a role in hindgut fermentation end products that are a non negligeable source of energy, evaluated up to 10% in broilers and up to 30% in pigs.
What do studies show?
Nguyen et al. (2020) also showed that more soluble NSP in the diet means lower pH in the lower gut, reflecting more fermentation of carbohydrates into SCFA, giving less opportunity for pathogenic bacteria to establish as described previously by Apajalahti (2005).
Insoluble fibre doesn’t influence digesta viscosity and can have benefits when fed at appropriate levels. When included in the diet, it is retained longer in the gizzard, stimulates HCl secretion from the proventriculus and results in reduced pH in gizzard content.
Low pH in turn stimulates pepsin activity in laying hens (Yokhana et al., 2016). Elevated fibre level by sunflower meal led to increased ileal digestibility of protein and fat and reduced energy digestibility (Kalmendal et al., 2011).
In recent decades, there has been an increasing number of studies in poultry, including layers, providing a solid base to revise the negative attitude to the fibre in poultry diets and to consider its role as a possible beneficial factor. These advances in fibre nutrition are even more important considering that to realise the genetic potential of the modern layer strains, it is necessary to raise birds with well-developed and functional gastro-intestinal tract.
Adding 3% of wheat bran in laying hens has been shown to also improve intestinal morphology by increasing jejunum villus height, villus height to crypt depth ratio and villus surface area (Abdollahi et al., 2020). Therefore, it is important to prepare pullets already in the developer phase (9-16 weeks of age) for the following production period.
In commercial conditions this is usually achieved by providing higher amounts of insoluble NSPs in the form of oat or barley hulls, sunflower meal, DDGS or other fibre rich sources in diets of pullets which in turn positively affects birds’ performance in subsequent laying period.
On the other hand, it should be stressed that soluble NSPs may play a role as substrates for beneficial bacterial fermentation in hind gut of birds.
Final compounds of such fermentation are butyrate and other SCFAs that provide energy for enterocytes, increase their proliferation, and limit the growth of pathogenic bacteria.
More recently, Gonzales-Ortiz et al. (2019) has developed a new category of product defined as “stimbiotic” that is incorporated as low as 0.1 g/kg inclusion rate that steers the hindgut microbiome towards a fibrolytic environment and allows it to extract more energy from undigested fibre. Due to the low level of inclusion this effect cannot be explained quantitively due to the negligible energy equivalency of 0.3 kcal/kg for the product (Ribeiro et al., 2018).
Several studies reported the beneficial effect from stimbiotic supplementation on microbiome modulation (Parra Perez et al., 2021) through the stimulation of the fibrolytic bacteria that results in higher SCFA, low pH and increased caecal bacterial enzyme activity (González-Ortiz et al., 2021).
Improved gut resilience helps animals to better cope with enteric challenges.
Recent studies in poultry (Rousseau et al., 2022) have demonstrated that the stimbiotic may be of interest to mitigate the enteric challenges that animals are facing in commercial production systems.
Studies in laying hens indicate the critical role of NSPs in layer production performance that reinforce the relevance to consider this criterion when formulating laying hens’ diets. Estimation of fibre levels in diets for laying hens should definitively go beyond the traditional crude fibre approach. Current research contributes to better understanding, not only of physio-chemical properties of NSPs compounds, but their functionality and role in nutrition.
However, more research is needed, as the introduction of NSPs as a parameter in diet formulations will require defining those NSP fractions and their levels and proportions that would be optimal for stimulating gut microbiome in a manner that improves nutrient digestion, ensures gut health, and thus birds’ performance.
The use of stimbiotic is a relevant strategy to promote dietary fibre fermentation and achieve better gut resilience to the birds facing multifactorial sources of challenges in commercial production systems.
Table 2. Different fibre contents in diets for peak layer production based on low and high fibre raw materials
|Ingredients, %||Low fibre||High fibre||High fibre/low density|
|Crude protein, %||15.9||15.7||15.7|
|Total dietary fibre||11.5||14.38||15.10|
*600FTU/kg phytase added with mineral matrix and 60 kcal AME
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