Feed ingredients with high concentration of dietary fibre, such as distillers dried grains with solubles (DDGS), are widely available and a price-competitive source of energy and nutrients for swine feeding programmes (Shurson et al., 2012).

In spite of being widely available and price-competitive, inclusion rates of these ingredients are limited because they contain high concentration of dietary fibre (DF) that decreases the nutritional value of the diet (Zijlstra and Beltranena, 2013). The nutritional value is reduced because DF increases variability in digestibility of energy and nutrients. Underfeeding digestible energy of nutrients, compared to the actual nutritional value, is costly because the full genetic capacity of the pig is not captured. Similarly, overfeeding digestible energy and nutrients is also costly because pig performance will not increase to capture value of the diet.

Therefore, "nutritional tools" are needed to quantify the energy value of feed ingredients with high concentration of DF and enable nutritionists to accurately capture the true nutritional value of each feed ingredient when formulating swine diets.

Dietary fibre is the sum of all plant derived carbohydrates that are indigestible to digestive enzymes in the gastrointestinal tract (GIT) of mammalians, e.g. pigs and poultry. However, these carbohydrates are not only indigestible to GIT enzymes of mammalians but they also reduce digestibility of nutrients (e.g. crude protein, lipid, and starch) and efficiency of energy utilisation (Gutierrez et al., 2014).

The objective of this work is to review current research by the University of Minnesota Swine Nutrition Group on the impact of DF in diets for growing and finishing pigs.

There are numerous definitions for dietary fibre but most of these definitions are based on analytical methods, or chemical physiological functions (Jones et al., 2006).

The simplest definition of DF is that it is composed of plant derived polysaccharides that are not degraded by digestive enzymes in the small intestine of monogastric animals.

The analytical definition has many more variations including (Figure 1): crude fibre, neutral detergent fibre (NDF), acid detergent fibre (ADF), total dietary fibre (TDF).

Therefore, regardless of analytical method, dietary fibre should include the following aspects:

1. indigestible portion of the diet
2. consisting in carbohydrates or lignin, and
3. that has physiological effects in the pig (NRC, 2012).

Figure 1. Differences between physiological and analytical classification of carbohydrates
(NRC, 2012)

These physiological effects of DF include modification of digesta transit time, laxation, binding of organic molecules in the digestive tract, water holding/binding capacity, solubility and susceptibility to fermentation (Schneeman, 1998).

However, many of these chemical entities do not accurately express the effect of DF on nutrient digestibility and energy utilisation. For example, a key question regarding dietary fibre is how much of it is degraded in the GIT and utilised for energy retention. Therefore, the researchers have used data from the literature to determine if the concentration of TDF is correlated to the concentration of DF (Figure 2).

Figure 2. Prediction of degradable fibre from concentration of total dietary fibre
(Urriola et al. 2010)

This low correlation suggests that the concentration of TDF does not predict how much of this fibre is actually degraded in the GIT of pigs.

Therefore, the Swine Nutrition Group at the University of Minnesota, has been using a series of in-vitro digestion and gas production techniques to characterise the composition and types of DF among feed ingredients for swine.

They collected 16 sources from three different kinds of high-fibre feed ingredients.

They selected corn DDGS, wheat straw and soybean hulls for their known inherent differences in digestibility.

Figure 3. In-vitro dry matter disappearance (IVDMD, per cent) after incubation with fecal microbes from growing pigs
(Huang et al., 2015)

The researchers used a series of enzymes (pepsin and pancreatin) that are regularly secreted in the stomach and small intestine of pigs along with fecal inoculum (Boisen and Fernandez 1997; Jha et al., 2011). After incubating 16 different sources of DDGS, wheat straw and soybean hulls with enzymes from stomach and the small intestine, theye observed that in-vitro dry matter disappearance (IVDMD) varies greatly among ingredients and among sources of each ingredient.

For example, among sources of DDGS, IVDMD varied between 46 to 62 per cent (Huang et al., 2014). Not only have they varied in the degradability in the gastric and small intestine digestion, but also in the degradability in the large intestine.

They measured in-vitro gas production that resulted from incubation of feed ingredients with pig faecal inocula, which is a mixing solution for faecal microbial to ferment, mainly including the pig faeces, macro-nutrients and buffer.

In conclusion, classifying and analysing sources of DDGS based on in-vitro degradability has greater benefit than current fibre analytical systems because it will provide a fast, accurate and less expensive "nutritional tool" to estimate nutrient digestibility in high-fibre ingredients, avoiding over- or under-feeding energy and nutrients to pigs.

The next steps will be to refine these in-vitro methods and measure the impact of various fibre degradation strategies such as utilisation of exogenous enzymes.

References

• Boisen, S. and Fernandez, J.A., 1997. Prediction of total tract digestibility of energy in feedstuffs and pig diets by in vitro analyses. Anim. Feed Sci. Technol. 68:277-286.
• Gutierrez, N.A., Serão, N.V.L., Kerr, B.J., Zijlstra, R.T. and Patience, J.F. 2014. Relationships among dietary fibre components and the digestibility of energy, dietary fiber, and amino acids and energy content of nine corn coproducts fed to growing pigs. J. Anim. Sci. 92(10):4505-4517.
• Jha, R., Bindelle, J., Rossnagel, B., Van Kessel, A. and Leterme, P. 2011. In vitro evaluation of the fermentation characteristics of the carbohydrate fractions of hulless barley and other cereals in the gastrointestinal tract of pigs. Animal Feed Science and Technology, 163(2):185-193.
• Jones, J.R., Lineback, D.M. and Levine, M. J. 2006. Dietary reference intakes: implications for fiber labeling and consumption: a summary of the International Life Sciences Institute North America Fiber Workshop, June 2004, Washington, DC. Nutrition reviews, 64(1), 31-38.
• NRC. 2012. Nutrient Requirements of Swine. The National Academies Press. Washington, DC.
• Shurson, G.C., Zijlstra, R.T., Kerr, B.J. and Stein, H. H. 2012. Feeding biofuels co-products to pigs. Opportunities and Challenges in Utilizing Co-products of the Biofuel Industry as Livestock Feed. FAO, Rome, Italy. p175-207.
• Schneeman, B.O. 1998. Dietary fiber and gastrointestinal function. Nutrition Research, 18(4):625-632
• Urriola, P.E. Shurson, G.C. and H.H. Stein. 2010. Digestibility of dietary fiber in distillers co-products fed to growing pigs. J. Anim. Sci. 88(7):2373-2381.
• Zijlstra, R.T. and Beltranena, E. 2013. Swine convert co-products from food and biofuel industries into animal protein for food. Anim. Frontiers, 3(2):48-53.

April 2015