Evidence suggests fiber offers more value than long thought.
By Gustavo Cordero and Gemma González Feed represents around 70% of the total cost of pork production. A large proportion (about 85%) of that feed cost comes from the need to meet the animal’s energy requirement in the diet, something usually achieved with starch protein and fat. In contrast, the contribution of fiber has been estimated to be between 1 and 4%. However, it could be higher – perhaps up to 8% – if swine diets are based on more fermentable fiber sources. Over the past few decades, there has been a largely negative perception of fiber with regards to feed consumption, digestibility and performance, but today there is more evidence of the value of fiber. The intestinal tract per se is not able to digest fiber but the organism takes advantage of the resident microbial populations which produce a repertoire of endogenous carbohydrases which are able to hydrolyze the non-starch polysaccharides (NSP) of which fiber is composed. The consequence of this activity is the production of short-chain fatty acids (SCFA) which have subsequent beneficial effects on intestinal function, animal production, animal health and also welfare. Recent studies aiming to evaluate the effect of fiber, either insoluble (e.g. wheat bran, oat hulls or straw), or soluble (e.g. sugar beet pulp) in pigs have demonstrated promising results on how these substrates influence the microbial populations in the gut. Increasing fiber in diets results in higher counts of lactic acid bacteria like Lactobacillus spp. and Bifidobacterium spp, and also butyric acid producers like Faecalibacterium prausnitzi, while Enterobacteriaceae and other coliforms or pathogen-like organisms are minimized. This shift in the bacterial populations leads to an increase in the fermentation activity, thus boosting the concentrations of SCFA and reducing the pH of the gastrointestinal environment decreasing the chance for pathogens to proliferate. The selection of the right fiber source and level of inclusion in the diet are critical parameters which may determine the success without damaging performance. It is also important to consider the age of the animal and understand what they can tolerate. Insoluble fiber in young animals can prevent post-weaning diarrhea. The addition of soluble fiber like sugar beet pulp to growing/finishing pig diets provides an easily fermentable fiber source which provides energy to the animal due to the maturation of the fermentative capacity of the gastrointestinal tract of older animals. The beginning of the utilization of NSP-degrading enzymes (NSPases) in the 1990s opened a new horizon in the exploitation of the fiber fraction of the diet. Xylanase is the most recognized enzyme in this category of products allowing higher levels of inclusion of fiber. Xylanases minimize the negative effects of NSP by hydrolyzing the soluble arabinoxylans, reducing digesta viscosity and consequently improving nutrient digestibility. Moreover, the prebiotic mode of action of xylanases has been associated with the production of xylo-oligosaccharides (XOS) in the gut, a compelling substrate for lactic acid producing bacteria which stimulates several pathways of interest. These activities influence microbiota composition and acidification of the gut environment, improving gut integrity and likely boosting intestinal immunity, and as a result, increasing animal performance. This may be the underlying mechanism explaining how xylanase supplementation reduces mortality (~ -0.55%) in pig production. The model describing the reduction in mortality with xylanase notes that the higher the background mortality, the bigger the effect of the xylanase and this can account for 43% of the variation. In spite of the limited number of observations (n = 34), the model offers a good fit (Figure 1). The response to xylanase supplementation is possibly linked with the ability to moderate subclinical disturbances, improving animal health and thus reducing mortality in pigs.
Figure 1. Mortality variation as a result of supplementing xylanase in function of the mortality of the control group in pigs
Recently, further evolving research in this field has led to the generation of a new category of feed additives, the stimbiotic. This category refers to those products which are able to stimulate a fiber-degrading microbiome to increase fiber fermentability when incorporated in the diet at doses which clearly are too low to contribute in a meaningful manner to SCFA. The benefit of the stimbiotic is that it does not directly provide enough substrate to bacteria for the direct production of SCFA but stimulates an NSP fermenting microbiome, including species such as Lachnospiraceae, Lactobacillaceae, Clostridiaceae and Ruminicoccocaceae. The degradation of fiber takes place more efficiently (Figure 2), pulling out more energy from the digesta and extracting value from a substrate that otherwise would be discarded in the manure. The evaluation of the stimbiotic, Signis, across different experimental studies (N = 10) has showed better performance results compared to the control group, but also a 2.1% reduction in mortality rates compared to xylanase supplementation. Dietary fiber has been associated with impaired nutrient utilization and reduced animal performance, but it is well accepted that a minimum amount of dietary fiber is required to maintain normal physiological functions. At present nutritionists know that fiber has more value than was once thought and needs attention to extract the greatest value out of it. It is important to understand its role in intestinal function. Through the stimulation of the microbiota in the gut, there is the chance to increase the utilization of fiber leading to a more fibrolytic environment and effective use of energy that would otherwise be voided. Xylanases, and to a greater extent stimbiotics, promote the production of endogenous NSPases, increasing the fermentative activity of the microbiota, and encourage the own animal’s mechanisms to utilize fiber in a more efficient way. Thus, these additives may reduce the issues that arise from the removal of antibiotic growth promoters from the production process.
Figure 2. Apparent total tract digestibility (ATTD) expressed as percentage of dry matter (DM), nitrogen (N), organic matter (OM) and energy in growing pigs supplemented or not with a stimbiotic
Since their entry into the market and through subsequent research programs, the benefits of xylanase, and more recently the use of stimbiotics, in pigs have demonstrated that they add more than nutrition, they also provide an unexpected health benefit, providing an extra value in the swine industry. References available on request.
Gustavo Cordero is Global Swine Technical Manager at AB Vista.Gemma González is Research Manager at AB Vista.
