Dietary fibre, the missing nutrient in pig production

The pig’s gut is a key factor for health and consistent performance. ‘Gut health’ is an underestimated factor. Not only is the gut a digestive organ, but also an important immunological organ. It is the largest organ system in a pig with a surface area of several hundred m2 (equalling the area of about two tennis courts). It is the largest contact surface between the organism and the environment and it consists of high activity tissue with an energy consuming metabolism.Modern livestock animals are typically fed high concentrate nutrient-dense diets to meet nutrient requirements. However, high-concentrated diets cannot meet physiological requirements. Animals need dietary fibre for optimal health and digestion. “Inadequate fibre supply is a co-factor for diseases such as MMA*, chronic colitis, dysentery and constipation,” said Prof Klaus Neufeld of the Animal Nutrition Research Centre in Austria. He spoke at the Agromed sponsored symposium on “Eubiotic fibre in profitable pig production: The missing nutrient,” on 8 May, in conjunction with the 2011 Pig Feed Quality Conference in Cebu, the Philippines.

The more concentrated feeds are, the less space available for fibre. And this can lead to disruptions in gut health. A minimal level of fibre is a prerequisite for optimal nutrition and ingredients metabolism. Dietary fibre consists of a heterogeneous group with different physiological effects. Fibre is not digested in the small intestine, but in the hindgut and/or caeca (depending on animal species).

The percentage of crude fibre in a diet does not equal the total dietary fibre. Fibre is a complex mixture of poorly characterised constituents. Dietary fibre is considered to be plant-cell skeletal remains that are resistant to digestion. Although primarily plant cell walls consisting of cellulose, lignin, and hemicelluloses, dietary fibre also includes soluble polysaccharides such as pectin, plant gums, and mucilages. Fibre is not totally carbohydrate because it includes lignin, which is a non-carbohydrate polymer. In addition, fibre is not totally unavailable, because a portion of dietary fibre is metabolised and converted to volatile fatty acids in the gastrointestinal tract of animals.

Shortcomings of crude fibre
In contrast to the current concept of dietary fibre, the older concept of “crude fibre” has serious shortcomings. The method for determining crude fibre consists basically of measuring the residue remaining after acid and basic hydrolysis (Weender analysis). It is known that the crude fibre method covers 50-80% of the cellulose, 10-50% of the lignin, and 20% of the hemicelluloses. It is clear that there is no fixed relationship between crude fibre and dietary fibre because plant cell walls vary in the proportions of their basic constituents.

The insoluble/non fermentable dietary fibre has an important function in the gut. Because of its high water binding capacity it enlarges the volume of the ingesta and promotes peristalsis of the intestines, accelerates colon transit and thus prevents constipation. In contrast, the soluble/highly fermentable dietary fibre is fermented in the colon and supplies nutrients for the colon flora, such as short chain fatty acids (acetic acid, propionic acid, butyric acid), which in turn contribute to stabilisation of the colon bacterial flora and reduce the risk of bacterial translocation. Buteric acid provides energy for the colon mucosa cells, which are important for water absorption and as such prevent diarrhoea.

For long, dietary fibre has suffered from a bad reputation: “It decreases digestibility”, “it dilutes nutrient density of diets” and “it decreases growth performance of animals”. But that is not true for all fibre sources. For example wheat bran or rice bran have to be added at 10% inclusion rate to increase the crude fibre content of a diet with 1%. To achieve this, sugar beet pulp is to be included at 5.5% and eubiotic (gut flora modulating) lignocelluloses (OptiCell a prebiotic fibre from Agromed) need only a 1.7% inclusion. It also has a much higher prebiotic effect (fermentation to lactic acid) than traditional lignocelluloses, beet pulp or fibre from citrus pulp. Table 1 shows how to qualify dietary fibre by the lignin content of different fibre sources. The difference between traditional fibre and eubiotic fibre is that the first contains no fermentable fibre.

Field trials
Besides the probiotic effect of eubiotic fibre, which selective supports lactic acid bacteria, it also has a preventative effect on pathogens, such as Salmonella. Prof Neufeld showcased several trials to illustrate the impact of eubiotic fibre. For example the Salmonella reducing effect was tested on a German farm (2008) with an evident Salmonella problem. For the trial 106 fatteners from 30-105 kg were used and split in two groups. One trial group received 1.5% eubiotic fibre (OptiCell) in the feed. Blood samples were taken and tested for Salmonella antibodies, which showed that the fibre group had a significant decrease of Salmonella positive pigs (control – 50% positive; OptiCell – <20% positive).

In a trial (2007) with sows at the University of Veterinary Medicine in Timisoara (Romania), differences in performance and behaviour between the control and the eubiotic fibre fed group were clearly seen. Adding eubiotic fibre had a positive effect on MMA symptoms, performance, faecal quality, animal behaviour, stress hormones and blood glucose level (Table 2).

Research at the Agricultural College St Florian in Austria in 2009 showed that the addition of eubiotic fibre to gestating sows until 3 days before farrowing reduced the duration of parturition significantly (215 min. vs. 151 min). A shorter time of parturition lowers the stress of birthing for the sow as well as for the piglets. And in weaners, Denkavit in the Netherlands (2009) compared the addition of eubiotic fibre and traditional fibre in diets that were based on barley and wheat (1.5% in weaner feed and 1% in starter feed replacing barley). On the measured parameters results were all in the advantage of the eubiotic fibre group (Table 3).

Fibre as a functional nutrient
Functional nutrients are nutrients or ingredients that have an effect on physiological processes, health or product quality beyond their established nutritional function. This is how Dr Robert van Barneveld of Australia-based Barneveld Nutrition defined functional nutrients in his presentation at the Eubiotic Fibre Symposium in the Philippines. “Strategic application is often required,” he said. “[They] must be matched to an environment, diet, production phase etcetera and their use requires a working knowledge of mechanisms. Often the nutrients do not confer the same benefits when isolated from ingredients regarded as rich sources, for example, selenium delivered to humans via consumption of pork or omega-3 fatty acids from fish oil.”

Fibre source and composition significantly influences responses in the pig, Van Barneveld said. The response to exogenous enzyme supplementation is variable and difficult to predict and moderate levels of soluble and insoluble non-starch polysaccharides (NSP) have limited effects on nutritional efficiency. He said that there are negative production responses to be expected at high levels of NSP, particularly from legumes.

With managing the nutrition of the pig, the aim is to assist the development and functional morphology of the gastrointestinal tract, meaning digestion and absorption of nutrients and protection against pathogenic invasion. Furthermore the aim is to manipulate bacterial populations to optimise gut health through competitive exclusion of pathogens and promotion of developing inherent immunity. Several feed additives are available for this purpose. “However, fibre is hardly ever considered,” Van Barneveld said. “Functional fibre certainly can play a role in this. Post weaning it can have a positive effect on luminal nutrition, cell turnover and differentiation, development of inherent immunity and can express prebiotic effects.” Luminal nutrition is the presence of food in the lumen or nutrient flow along the gut, which is a powerful stimulus for development of the GI tract. Absence of nutrients results in a decreased rate of cell differentiation and cell turnover and the inability to maintain the structure and function of the intestinal mucosa. Villus heights will be reduced; there is a direct positive correlation between feed intake and villus height.

Fibre and gut recovery
Van Barneveld said that there are some precautions in feeding fibre, because there are good fibres and bad fibres. They positively or negatively influence viscosity and fermentation, and contaminants of course can ruin quality. One type of dietary fibre that can be used is inulin (fructoologosaccharides) which is mainly derived from chicory roots (Cichorium intybus) or yácon roots (Smallanthus sonchifolius). Inulin is a highly fermentable carbohydrate and thus provides energy. It provides protection through changes in bacterial community structure of the gut and encourages the growth of propionic acid producing organisms and also promotes the selective growth of bifidobacteria (inhibitory to pathogenic microorganisms).

Inulin in trials expressed a reduction of swine dysentery when challenged. High fibre intake, however, can have a negative effect on threonine requirements. Threonine is found in high concentrations in gastro-intestinal secretions and it has a function in protecting the intestinal mucosa from digestive proteases, prevent dehydration of membranes and protect the gut wall from pathogenic invasion. Threonine requirement may be increased when mucin secretion is increased. The gut of the piglet uses 55% of the threonine intake and the requirement is 3.4-3.7 g/100 grammes of CP.

The effect of functional fibre in growers is limited, according to Van Barneveld. Fibre can optimise nutritional efficiency and with fibre the digesta transit time can be manipulated, but there is asynchrony of nutrient supply. “One needs to understand the response of growers to specific forms of fibre. You cannot generalise,” he said.

Fibre for sows is mostly given pre-farrowing. It can assist in the management of udder oedema and MMA. It is important to closely monitor faecal consistency and avoid constipation. Fibre influences the digesta transit time and helps maintain a healthy gut flora. In sows fibre in the diet is also often used to obtain satiety without the sows becoming too fat. Table 4 illustrates this and gives some data about the water holding capacities of some fibre sources.

It is very unlikely that low inclusion of high quality fibre dilute energy intake in sows. But it will promote digesta transit time. Sows have a much higher fermentation capacity than growers, especially of crude fibre. They also have a massive capacity for intake and can easily compensate, especially if gut fill is promoted during gestation.Formulating for “fibre” is still difficult, because it is not really a nutrient, Van Barneveld explained. When using crude fibre as a constraint it should be limited to <2.5% in piglet diets (low crude fibre ingredients) and 4-6% in sow diets (drives inclusion of known ingredients like millrun, wheat bran, lucerne meal). Using dietary fibre as a constraint lacks analysis and will include resistant starch. Most research is related to human nutrition and health and thus difficult to extrapolate to pigs.

*MMA = mastitis (udder infection), metritis (inflammation of the lining of the uterus), agalactia (absence of milk).