Feed additives

Background

Glycerides of butyric acid: A must for poultry

That butyric acid is beneficial for intestinal health and growth performance, especially in young and vulnerable animals, is well known. However, the practical use of butyric acid entails some challenges. Framelco developed products based on butyrate glycerides in order to bring butyric acid to the lower part of the gastrointestinal tract (GIT). Interestingly, these glycerides also have shown to positively affect the carcass quality of broilers.

Among the short chain fatty acids, butyric acid has special properties. It is a natural substance in mammals and birds, normally produced by the microbiota present in the lumen of the caecum and large intestine. Although a lot is yet to be discovered about this fatty acid, literature extensively describes its strong capacity to improve intestinal health. Besides being the preferred fuel for colonic enterocytes, the most known effect of butyric acid is stimulating epithelial cell proliferation and differentiation. It also has a beneficial effect on the colonic barrier function.

Photo: David Rozemeyer
Photo: David Rozemeyer

Other effects of butyric acid include stimulation of enzyme secretion and stabilising the microflora, resulting in a more efficient nutrient digestibility and better colonisation resistance. Hence, improved growth performance is observed, especially under suboptimal circumstances. That is why worldwide, where the preventative and curative use of antibiotics is becoming more and more restricted, butyric acid is a popular feed additive in young animals.

Take maximum advantage of butyric acid

So far, the good news. There are also some difficult aspects of butyric acid. In its free form, butyric acid is corrosive and has an incredibly bad smell. Butyric acid is a weak acid with a pKa value of 4.82. This means that, in the intestinal tract with mainly a neutral pH, it will be very rapidly metabolised in the crop and the upper gastrointestinal tract. Suppliers started to use salts of butyric acid, primarily sodium and calcium butyrate. This solid and generally odourless form is much easier to handle. One problem however remains, and that is the fact that butyrate salts are absorbed in the upper part of the GIT. This in turn is very disadvantageous as pathogenic bacteria, like Salmonella, colonise in the caecum and colon. The most common way to handle this, is using micro-encapsulation or fat coatings. Salts of butyric acid are released at the moment the coating is broken down by lipase in the small intestine. In case of poor coating the active product is most probably released too early, whereas in case of a proper coating the amount of butyric acid in the product is relatively low, e.g. about 25%.

To overcome all former disadvantages, Framelco developed a third-generation butyric acid in the form of glycerides. Glycerides are produced by esterifying 3 molecules of butyric acid to a glycerol molecule resulting in ‘tributyrin’. Tributyrin therefore contains a relatively high amount of butyric acid, but is non-corrosive, odourless and pH-independent and is therefore able to reach the lower parts of the gastrointestinal tract. Studies show a significant effect of butyrate glycerides on the composition of the caecal microbiota of broilers, indicating that the glycerides indeed were able to reach the lower part of the gastrointestinal tract. Several strains of Bifidobacteria were significantly increased in relative abundance. Benefits associated with increased numbers of Bifidobacteria in the intestine include immunostimulation, competition with pathogenic bacteria for nutrients and attachment sites, and production of volatile fatty acids that provide metabolic energy for the host.

The favourable effects of tributyrin

The beneficial effect of tributyrin in broilers has been confirmed in literature. One hundred and twenty Cobb broilers were challenged with lipopolysaccharide (LPS) and either non-treated (control) or treated with tributyrin or coated sodium butyrate. At day 43 the chickens were euthanised to study intestinal morphology. In contrast to the control group and coated sodium butyrate, tributyrin significantly increased villus height in the ileum (Figure 1). This also confirms that tributyrin can reach the lower part of the intestinal tract. In addition, villus: crypt depth ratio in the ileum was also improved by tributyrin and to a lesser extent by coated sodium butyrate. The researchers concluded that tributyrin was more effective than coated sodium butyrate in alleviating the harmful effects of LPS.

Figure 1 – Effect of tributyrin and coated sodium butyrate on villus height in LPS challenged broilers.


Next to the proven effect of butyric acid on intestinal health and growth performance, an interesting new phenomenon has been observed with the use of tributyrin. Dietary addition of butyrate glycerides not only significantly improved the final body weight and body weight gain of young broilers, but also decreased the relative abdominal fat weight. Butyrate glycerides were able to reduce body fat deposition via regulation of the expression of genes, which are involved in processes like lipid and fatty acid transport, fatty acid oxidation, and cholesterol metabolism. It was also emphasised that tributyrin was able to modulate lipid metabolism. Supplementation of butyrate glycerides decreased relative abdominal fat weight and increased relative breast muscle weight at five weeks of age (Figure 2). In another study, the positive effect of butyrate glycerides on carcass quality was confirmed as a decreased abdominal fat deposition was found. It was suggested that the increased amount of Bifidobacteria, that was found in the caecum, may have contributed through the production of choline metabolites. Choline metabolites participate in the packaging and transport of triglyceride in the blood and are therefore able to modulate lipid metabolism.

Figure 2 – Effect of butyrate glycerides (1kg per tonne of feed) on relative breast muscle weight and relative abdominal fat weight in broilers (at 5 weeks of age).


Conclusions

Several forms of butyric acid are available in the market, developed to increase the effectiveness in the gut and to deal with its bad smell. However, the glyceride form seems to outperform the other butyrate solutions. This is proven by the fact that butyrate glycerides are very effective in supporting intestinal health. Both by improving gut integrity as well as by increasing biodiversity of the microbiota. This results in a higher growth performance, proven by several experiments all over the world. Moreover, recent research shows that butyrate glycerides positively influence carcass quality by altering gene expression involved in fat deposition and via supporting the growth of Bifidobacteria in the caecum. Promising results for the future!

References available on request

Author: R&D team, Framelco