“Fibre”: necessary paradigm shift in pig feeding

In performance-oriented pig feeding, nutrient-rich and highly digestible diets are standard. In this context, the topic of "fibre" in pigs has long been associated with dilution of energy, reducing digestibility, feed conversion and performance. Currently, however, the perspective has changed and the importance of fibre for digestion, health and animal welfare is increasingly in focus.

This view has its origin in human nutrition indicating that dietary fibre can have a large influence on reducing the incidence and severity of diarrhoea, constipation and reduction of inflammation. Dietary fibre is increasingly considered as a prerequisite for “intestinal health” which is characterized by a stable, balanced microflora that is able to suppress pathogenic bacteria.

Many challenges remain before fibre for swine achieves the same status it holds in human nutrition. A step on this path is the reconsidering of the terminology used for “fibres”. A good example comes from Germany. The German Animal Welfare Regulation (TierSchNutztV, 2006) requires a minimum content of 8% crude fibre per kg of dry matter in the feed for pregnant sows or a daily supply with at least 200 grams of crude fibre per animal. These requirements are established against the background of animal welfare (environmental enrichment, satiety and the associated reduction of aversive behaviour). The term "crude fiber" is thus fixed by law and is also commonly used as a synonym for "fibre". At this point, a first dilemma reveals: from the point of view of modern animal nutrition, the crude fibre from the Weender feed analysis developed in the 19th century is completely inadequate. The dilemma widens on closer examination of the expectations regarding the "fibre": it should have positive effects on digestion, satiety, environmental enrichment and health - but these effects are not associated with "crude fibre".

In Europe, the topic of environmental enrichment is gaining in importance. Regarding the fibre, it should be considered separately from health or digestive effects. Unlike the other factors, impacts of fibre on environmental enrichment can actually be attributed to specific feed materials (hay, straw, maize silage).These are structured fibre-rich roughages with low energy density, often given via separate troughs, that provide long eating and attraction time. Effects are measurable in animal welfare aspects (e.g., reduction of tail biting, reduced aggressiveness). Increasing fibre intake with these forms of roughages can also have a positive impact on the other mentioned factors, but these are not the focus of this strategy.

Digestion, satiety and health are much more complex. A variety of positive effects of fibre for pigs is described in the literature and also visible in the field. Examples are the improvement of intestinal peristalsis/ passage rate with improved defecation, support of intestinal health and immune competence, higher proportion of metabolic fermentation products in the hindgut (short chain fatty acids SCFA), reduction of diarrhoea, shortening farrowing time in the sow, etc. These effects result from various properties of the fibre, e.g. viscosity, solubility, fermentability or swelling capacity.

The targets differ greatly. While in pregnant sows, a high level of satiety with reduced feed intake is desired, the opposite applies for the lactating sow and the growing pig. In piglet feeding, a reduction of the occurrence of diarrhoea and promotion of intestinal health are the main goals.

This results in different demands on "fibre" or on the feed used as fibre carriers. Not all the effects of the "fibre" can be described by a single analytical parameter due to the large number of chemical and physical properties and their interactions. They are not associated with a single feed material as fibre carrier - effects achieved in the animal depend solely on the characterization of the total diet.

"Fibre" is the generic term for a variety of plant cell wall carbohydrates, which cannot be hydrolysed by the body's own enzymes of the small intestine. One of the most important physiological properties is that, depending on the composition, gut bacteria can ferment them. Insoluble, non-fermentable fibres regulate peristalsis in the gastrointestinal tract. Soluble fibres enhance viscosity and tend to have negative effects on nutrient absorption but are more often colon-fermentable. The classification of the fibre fractions is shown in Figure 1.

Neither the “crude fibre” nor the ADF (acid detergent fibre)/NDF (neutral detergent fibre) take into account the importance of soluble fibres, while both non-starch polysaccharides (NSP) and dietary fibres are chemically divided into "soluble" and "insoluble" fractions. This differentiation is important for the properties of the fibres, as shown in Figure 2 below:

The distinction between non-fermentable and fermentable fibres is an essential feature of the insoluble fibres, but an analytical differentiation is currently not possible.

The pig needs a combination of fibres with different properties. Unfortunately, there are currently no reliable recommendations, but apart from practical experience. French recommendations (Lebreton, 2017) for sow feeding refer to soluble and insoluble dietary fibres (Table 1).

Proportions of more than 20% dietary fibres appear to be unusually high compared to the usual "crude fibre values" know from feeds, but on closer inspection of levels measure in feed materials (Table 2), they are realistic compared to crude fibre contents.

Especially the Lignocellulose products contain high amounts of insoluble and fermentable fibres. In other fibre components, there are no comparable proportions. Low amounts of lignocellulose provide high proportions of the desired fibre fractions into the diet.

One aspect that is common among all production stages is the need for an affordable concentrated source of fibre so as not to dilute the diet with nutrient-sparse fibre sources. Lignocelluloses generally meet these requirements, but there are some differences between sources. A clear distinction can be seen between first and second generation Lignocellulose. The first generation consists of 100% insoluble, nonfermentable fibres. It has a strong "physical" effect in the gastrointestinal tract. The micronization (average particle size 50-120 μm) ensures a high number of inert particles with a large surface area, which helps to regulate peristalsis. This prevents the ascension of pathogens and shifts microbial fermentation to the rear section of the colon.

Adding to this physical mode of action, the insoluble fibres of the second generation lignocellulose are partially fermentable, leading to a prebiotic effect and additional physiological effects, specifically, the production of butyric acid through fermentation. Butyric acid is, by now, well known for being highly beneficial for intestinal tissue.

The use of fibre-rich feedstuffs for satiety in gestating sows, as well as for prophylactic treatment for constipation and MMA (mastitis, metritis, agalactia) issues, is standard practice, however, the specific mode of action is quite complex. Constipation continues to be a major concern in gestating sows for both production and obvious welfare reasons. Fibres can alleviate this issue by promoting peristalsis through interaction with the gut mucosa, and by keeping the ingesta bulky and moist to ease its passage through the intestinal tract. This “bulking” effect also has implications in sow satiety as it helps to create a feeling of physical “fullness. The other main type of satiety is physiochemical; its mode of action is complex in itself, but is mainly linked with stable blood glucose levels controlled by the short chain fatty acids produced in the hindgut.

Fermentable fibres play an important role here, as they produce energy long after the digestion of other feed components is finished. Colonic fermentation can cover up to 30% of a sow’s maintenance requirements. This leads to a more continuous release of energy from the diet and can effectively prevent sudden peaks and drops in blood glucose levels. Major risk factor for MMA are, in addition to obese sows, constipation before birth as well as starvation periods in the late pregnancy phase (decrease in blood glucose level). Feeding fibre to sows can affect the piglets in other ways as well. The SCFA produced by fermentation can be transported throughout the body via the blood stream; this includes the placenta where blood-borne SCFA can provide additional energy for the growing litter, independent of sow blood glucose levels. This can increase the growth of piglets, leading to heavier birthweights. The longer energy release can also help reduce farrowing times by continuing to provide energy for the sow even after she goes off feed pre-farrow. The consequence of this is generally a reduction in the number of stillborn pigs. A study by Baarslag et al. (2013) was able the capture these three phenomena by feeding a fermentable lignocellulose at 1% for just 1 week prior to farrowing. (Table 3)

If the sow is stabilized by an adequate supply of fibre during the time of farrowing, the piglets will benefit as well. A high feed and water intake of the sow ensures sufficient colostrum and milk production. Together with the reduced incidence of MMA and shortened farrowing, this gives the piglets an optimal start.

The benefits do not stop at birth though, as the first bacterial colonization in the piglet (about 80% of the total flora within three hours after birth) comes from the microflora of the sow. Feeding sows fibres that will promote the growth of beneficial microbes, will give these microbes an advantage over pathogenic types when it comes to the colonization of the piglet.

In this context, a study of the University of Veterinary Medicine Hannover (Leurs, 2016) showed that a fibre rich diet fed in the period from one week pre partum to weaning could significantly reduce the incidence of Clostridium perfringens (measured immediately after farrowing) in sow manure compared to a standard diet.

Perhaps the most critical change occurs at weaning as the piglet shifts from a liquid to solid diet. During this time, the microflora takes on an entirely different form as microbes specialized in digesting solid feed components replace the existing “milk” specialists in their prominence. This change coincides with stress, insufficient feed intake and digestive enzyme activity and atrophy of villi. Consequently, the intestinal transit time is prolonged.

This extension from a normal value of 50-70 h allows the pathogenic bacteria in the intestine optimal time to multiply and in many cases causes diarrhoea. Results of a study by Schnabel et al. from 1983 clearly show how effectively an increase in fibre content from 0.5% to 5.5% crude fibre can normalize the intestinal transit time in the period after weaning (Figure 3).

The insoluble dietary fibres are responsible for the effects of a shortened transit time. A study (Table 4) compared a weaner diet low in dietary fibre (DF 7.3%) with high dietary fibre diets (DF 14.5%) where the fibre source was either soluble (pectin) or insoluble (barley hulls).

The feed intake and weight gain in piglets receiving the diet high in soluble DF were clearly reduced compared to the low DF diet while the parameters were improved with the supply of highly insoluble DF. In addition, the insoluble dietary fibre also supported the gut integrity by increasing the villi length.

Soluble fibre is therefore not the tool of choice for the piglet - at most in addition to sufficient amounts of insoluble fibre.

Insoluble and concurrent fermentable fibre can sustainably improve intestinal health and performance in the piglet. The avoidance of diarrhoea and the control of pathogenic germs are of particular importance. In an Australian trial, increasing levels of insoluble NSP (2nd gen. lignocellulose) were fed to weaned piglets and positively influenced their growth and intestinal health parameters. In addition, increasing levels of lignocellulose reduced the incidence of E. coli and increased the butyric acid-producing Christensenellaceae (Figure 4).

The composition and properties of dietary fibres in the feed used as "fibre compounds" in pig feeding differ significantly. The effects in pigs go well beyond the saturation of the pregnant sow - not at least because the topic of intestinal health and its impact on performance is becoming increasingly important. The "crude fibre" has served its purpose, but numerous investigations are still needed to qualify and quantify the effects of different fibre fractions. The goal must be, not to reduce the positive effects to the effect of the feeding of “fibrous” components but to provide reliable feeding recommendations for fibre classes (insoluble/soluble/fermentable).

Baarslag L. et al. (2013): Wirkung eubiotischer Lignocellulose auf die Abferkeldauer von Zuchtsauen, Proceedings 12. BOKU-Symposium Tierernährung, 175-178. Wien, Austria.

Braach, J. et al. (2017): Charakterisierung verschiedener Faserquellen mittels Wasserbindungs- und linearisierter Pufferkapazität. Proceedings 16. BOKU-Symposium Tierernährung, 64-67. Wien, Austria.

Hedemann, M.S. et al. (2014): Intestinal morphology and enzymatic activity in newly weaned pigs fed contrasting fiber concentrations and fiber properties. J. Anim. Sci. 84: 1375–1386.

Jenkins, N.S. et al. (2015): Relationships between diets different in fibre type and content with growth, Escherichia coli shedding, and faecal microbial diversity after weaning, Anim. Prod. Sci. 55: 1451.

Lebreton, P. (2017): Key moments in the Asian Sow Cycle: how can we leverage them by using functional ingredients? Contribution of special fibres on gestation, farrowing and birth performance. Presentation at Performance Conference 2017: “Managing hyperprolific sows in Asia”. Bangkok March 14th 2017.

Leurs, M.M. (2016): Einfluss unterschiedlicher Fütterungskonzepte im peripartalen Zeitraum und der Laktation auf die Gesundheit und die Körpermassenentwicklung von Sauen und Ferkeln. Dissertation University of Veterinary Medicine Hannover.

NRC (2012): Nutrient Requirements of Swine. 10th rev. ed. Washington, D.C: Natl. Acad. Press

Swords, W.E. et al. (1993): Postnatal changes in selected bacterial groups of the pig colonic microflora. Biol. Neonate 63: 191–200.

TierSchNutztV (2006): Verordnung zum Schutz landwirtschaftlicher Nutztiere und anderer zur Erzeugung tierischer Produkte gehaltener Tiere bei ihrer Haltung. Bekanntmachung vom 22. August 2006. Geändert durch die Verordnung vom 30. November 2006. Bundesgesetzblatt I: 2759.