Background last update:6 Aug 2012

Lignocellulose: fresh wood as dietary fibre

Dietary fibre is an important animal feed ingredient because many different fractions of fibre components have a positive effect on the digestive process. Lignocellulose made from fresh wood is a relatively new addit ion to the dietary fibre group and recent trials show positive results in pigs and poultry. BY Dr Arthur Kroismayr.

Fibre is an essential part in animal diets, especially in sows, but there has to be a distinction between different groups of fibre components. The traditional term “crude fibre” in the Weender Analysis is not precise enough anymore. In this analysis only cellulose is fully detected and other important dietary fibre components like hemicelluloses, lignin and pectin are not or only partly detected.
Traditionally, lignocellulose products consisted of fine wood meal derived from one wood source. Recent lignocellulose products contain different varieties of wood due to different physiological effects of those plant derived materials
The Van Soest analysis differentiates dietary fibre contents much better. This analysis divides neutral detergent fibres (NDF), acid detergent fibres (ADF) and acid detergent lignin (ADL) contents. *Figure 1 and Table 1 show how dietary fibre can be fractioned using different methods. Nowadays, modern enzymatic methods are used to best fractionate dietary fibre and to get information about the total dietary fibre (TDF) content of feedstuff
Effects on the gut
Besides a distinction in different dietary fibre contents, it is also possible to classify soluble and insoluble fractions and fermentable and non-fermentable fibres. Generally spoken, soluble fibre components can be fermented while insoluble fibre cannot or can only poorly be fermented. Water-binding activity of insoluble and non-fermentable fibres is also important, because of the resulting stimulation of the gut mucosa. A lot of water-binding activity could lead to a saturation effect on the one hand and to an accelerated passage rate on the other. In addition, if the crude fibre content of diets is relatively high, saturation effects may cause decreased feed intake and therefore maybe decreased performance. This will be a problem in growing and fattening animals. Fibre is also important for physiological processes in the gut. In a correct inclusion rate, non-fermentable fibres will accelerate the passage rate in the caecum and colon which will prevent animals from constipation. Accelerated passage rate is important to maintain gut health and physiological water re-absorption.


Fibre in the large intestine

How well the fibres can be fermented by the animal is very important as this causes a major difference in physiological activity. Fermentable fibre components arrive in the large intestine undigested and can be metabolised by gut micro flora. Inulin, fructo-oligosaccharides and pectin (fermentable dietary fibre components) are fermented rapidly and nearly completely within the colon being nutrients for intestinal flora. Especially so-called 'positive' gut micro-flora metabolises fermentable fibre and as a result, short chain fatty acids such as acetic acid, propionic acid and butyric acid and additionally lactic acid are produced. These fatty acids can be easily reabsorbed in the colon and therefore they are easy available energy for the animal.

Lignocellulose is sold with different particle size. Left shows very fine/mealy lignocellulsoe and right shows a crumbled version of the product.

One of these three, butyric acid, plays another important role in the gut as it is a substrate for mucosa cells and important for regeneration of the whole mucosa. This means that higher production of butyric acid in the colon, reached by accelerated passage rate, will lead to an improved gut health status. Additionally, the potential of colonial mucosa cells to reabsorb water out of the chyme means that faeces consistency is directly influenced by production of butyric acid. Due to the pH decreasing effect of short chain fatty acids, the colonial microflora is stabilised and translocation of pathogenic bacteria from the colon to the small intestine can be avoided. Lowering of pH and influence on colonic flora decreases ammonia concentrations in the ingesta which again improves gut health status and energy supply of the animal because ammonia is a toxic substance and detoxification needs a lot of energy.

Lignocellulose, made from fresh wood, has been used as a high quality dietary fibre source in animal nutrition since a few years. Compared to other traditional fibre sources, lignocellulose is characterised by its high crude fibre content (>55%) which saves space in rations for other valuable components. In addition, lignocellulose contains no mycotoxins, which can be a big problem in wheat bran for example. To create dietary lignocellulose products, it is necessary to process wood to a very fine particle size; otherwise it can not be used in animal nutrition due to negative effects on the gut wall of animals.

Fermentable fibre components of some lignocelluloses are a selective growing medium for lactic acid bacteria which can also be explained as 'prebiotic' effect of these lignocelluloses. All in all, right combinations of fermentable and non-fermentable fibre components will enhance digestive processes and lead to improved gut health status of animals. Attention has to be paid on good product quality (particle size, free of any residues, constant product quality) which can be provided by some specialised producers. Wood shavings, which in some areas are advertised as 'lignocellulose' products, are not suitable for animal nutrition – they can even be dangerous in animal feed and destroy animals' gut.

Fine wood meal
Traditionally, lignocellulose products consisted of fine wood meal derived from one wood source. The main effect on animals of these products was caused by nonfermentable dietary fibre components which means positive effects on passage rate, gut peristalsis and therefore gut health status. Recent lignocellulose products contain different varieties of wood due to different physiological effects of those plants. It seems to make sense to use lignocellulose products which both contain non-fermentable and fermentable dietary fibre.

Such combinations will combine positive effects of traditional lignocelluloses with 'prebiotic' effects of fermentable fibre. Recent scientific data shows that non-fermentable dietary fibre leads to a dislocation of important fermentation processes from caecum to colon. In the large intestine fermentable parts of the diet can be metabolised ideally and improve digestive processes. The fermentable dietary fibre components are additional nutrients for colonic micro flora including all well known positive effects.

Use in pigs
Due to the high fibre demand of gestating sows, lignocellulose is used in relatively high dosages (2.5%). Investigations in Germany showed that a combination of fermentable and non-fermentable lignocellulose (OptiCell®, Agromed Austria) led to significant lower feed intake in an ad libitum feeding system. Such feeding systems are positive regarding animal welfare but in the past they were not easy to realise due to danger of too high a feed intake of breeding sows. With the used lignocellulose product this problem could be solved.

Additionally, the use of this lignocellulose combination led to lower excretion of the stress hormone cortisol (minus 22.6%) compared to a control group receiving only beet pulp for dietary fibre supply. The same effect was observed in a scientific trial with breeding sows at the University of Temeswar in Romania. Trial results also showed that the lignocellulose product had a positive impact on faecal quality of treated sows. For practical use lignocellulose seems to be very suitable especially in sows. The high crude fibre demand of breeding sows can easily be satisfied with relatively low inclusion rates of lignocellulose.

The impact of such dietary fibre products will lead to improved passage rates and decreased risk of constipation. The positive effect on satiety will lead to a stress relieving effect due to lower excretion of cortisol which is related to a more constant blood glucose level if animals are not hungry (glucomodulation). In weaning piglets and fattening pigs, lignocellulose could be used with a lower inclusion rate. A higher saturation effect is not wanted in growing pigs but this effect of lignocellulose depends on dosage. Studies showed that inclusion of 1 to 1.5% of the above-mentioned lignocellulose product led to improved growth performance and quality of faeces in piglets.

Dr Arthur Kroismayr studied Agricultural Science (Specialisation in Animal Sciences) at the University of Natural Resources and Applied Life Sciences (BOKU) Vienna. In 2003, he started his PhD in animal nutrition, with the topic mode of action of essential oils in pigs and worked as Product Manager for phytogenic feed additives at Biomin. In October last year, he took up the position as Research Director at Agromed in Austria.

In an independent study conducted at UFA AG in Switzerland 228 weaned piglets (average age 27 days) were allocated to two trial groups. The negative control group received a standard weaning diet containing organic acids and feed enzymes but no special fibre addition. In the lignocellulose group, 1.5% of the product was added 'on top' of the control diet. Both diets showed very similar values of nutrients, except the fibre content which was lower (3.1%) in the negative control group compared to the lignocellulose (4.1%) group. The feeding trial lasted 35 days. Inclusion of lignocellulose led to higher daily weight gain (+6%) and improved feed intake (+3.6%) while feed conversion rate was more or less the same in both groups. The same was observed in a scientific study with weaning piglets at University of  Veterinary Medicine in Vienna, Austria. In this 45-day experiment 'on top' inclusion of 1% of the mentioned lignocellulose product led to higher daily feed intake and growth rates, while the feed conversion rate was not influenced.

This result is especially interesting as energy and protein content was diluted in the trial group because the lignocelluloses product was added 'on top'. It seems that the combination of non-fermentable and fermentable dietary fibre has a positive effect on digestive processes and nutrient metabolism. This thesis is confirmed by improved consistency of faeces which was also observed in this scientific study.

Poultry and ruminants
Lignocellulose as dietary fibre is also used in broilers and turkeys. Although fermentation processes in the gut are of minor importance in poultry nutrition, fermentable lignocellulose components lead to similar positive effects (faeces consistincy, gut health status, performance parameters) like in other monogastric species. Further research has to be conducted to investigate scientifically the impact of this dietary fibre in birds.

For young ruminants and especially calves the same fact has to be mentioned. Lignocellulose is already used in milk replacers due to its positive effects on gut health status and to prevent (nutritional) diarrhoea. These effects are not surprising as young ruminants are monogastric animals and mode of action of such fibre combinations are well investigated in pigs. 

Source: Feed Mix Volume 16 No. 02

* For Table 1 and Figure 1, please click on the link below.

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