Phenolic compounds have attracted a great deal of research interest in human nutrition and medicine during the last decade. Nevertheless, animal nutrition still lagged behind in recognizing phenolics as an interesting field of potential feed additives.
It is a fact that in the past there has been great concern over the anti-nutritional effects of some members of the phenolics family. An example is the case of high concentration of condensed tannins in animal feeds when certain sorghum varieties were used. Contemporary thinking, however, is focusing more on the beneficial effects of phenolics, and this has shed new light in the usage of these compounds as alternative additives in animal feeds. Preliminary results are quite promising.
What are phenolics?
Phenolics are an immense group of over 8,000 diverse compounds that are products of plant secondary metabolism. All phenolic compounds share an aromatic ring with one or more hydroxyl groups in their chemical structure. Commonly known phenolics include names such as flavonoids, tannins, oligomeric proanthocyanidins and lignans. A basic feature of phenolics is their significant antioxidant activity. However, some phenolics may have additional beneficial properties applicable to animal gut health, such as anti-inflammatory or antimicrobial activity. All these diverse properties are the driving force of existence for these bioactive compounds in plants, where they serve as pigments, structural components, defense compounds, antioxidants, etc.
Some phenolics may have additional beneficial properties applicable to animal gut health, such as anti-inflammatory or antimicrobial activity.
To illustrate the widespread presence and universal potential of these compounds commonly found in animal feeds, four feedstuffs are examined, each with a different makeup of phenolics.
Chestnut wood (Castanea sativa) is a good source of hydrolyzable tannins, which are not chemically and physiologically the same as condensed tannins. The latter have been associated with anti-nutritional properties when fed at high concentrations through certain sorghum varieties. On the other hand, hydrolyzable tannins at the right dosage are currently considered as a next generation additive with many beneficial properties on gut health and beyond. It has been postulated that the mechanism(s) by which chestnut tannins exert their beneficial effects in monogastric animals is by improving feed palatability, by stimulating digestive secretions and by slowing peristaltic movements. Most likely it has been demonstrated that hydrolyzable tannins can modulate the interaction between microbiota at the gastrointestinal tract level through their antimicrobial properties. Perhaps these phenolics behave in a manner similar to zinc oxide, which is known to cause such a beneficial balance in gut microbiota. Indeed, such gut health benefits have been observed in broilers (and piglets) where litter quality was improved due to firmer excreta consistency. Certainly, the use of hydrolyzable tannins deserves closer attention by the scientific community.
Pinewood in the form of finely milled powder is currently used as a valuable source of lignocellulose (functional fibers) in pig and poultry diets — and also in pets — in order to improve gut motility and gut health due to its strong prebiotic properties. However, there are additional components in pinewood, especially in the outer sections of the wood, which can be the source of additional health benefits for animals. Pinewood is rich in flavonoids such as taxifolin, lignans such as pinoresinol, and especially rich in oligomeric proanthocyanidins (OPCs). These OPCs are powerful antioxidants; even more potent than vitamins C and E. It has been documented that phenolics in maritime pine (Pinus pinaster) bark have much higher antioxidant activity, comparable to that of other natural food antioxidants such as cinnamon. It would be interesting to isolate these compounds and test them under laboratory conditions, but currently it is less expensive to feed them through pinewood powder — something that is already done to enrich feeds with lignocellulos. This is an example of the possibility of combining the properties of fiber and phenolics in an existing single package.
Pinewood powder is an additive that offers the combined effects of functional fiber and a great array of phenolic compounds with diverse actions. | Anna Cvetkova, Dreamstime.com
It is well known that oat groats (steam-flaked dehulled oats) are being used as a prime ingredient in high quality piglet diets. Whole oats (Avena sativa), on the other hand, are a choice ingredient for valuable racehorses. Oats provide a valuable tool in the treatment of gastrointestinal disorders in young pigs and other animals. Their high quality fiber is considered to be the driving force behind this beneficial effect. But, there might be also other bioactive molecules in oats that could contribute to their beneficial effect in the gut. One such group of biologically active compounds is called avenanthramides. This group consists of more than 20 phenolic compounds found in oats but not in any other cereal. Recent studies have shown that they have both an anti-inflammatory and antioxidant effects. In addition, they have attracted considerable interest in dermatology due to their anti-irritant and anti-itching effects on skin. Perhaps their cell healing properties extend to enterocytes, and, as such, they contribute to the high gut health associated with oats feeding. It might be discovered that oat fiber is not as valuable as currently thought, if avenanthramides prove to be the "secret" ingredient of success for oats.
Oats are the only cereal with a unit family of phenolics with strong antioxidant activity. | Elzbieta Sekowska, Dreamstime.com
Another rich source of phenolics are the by-products of the winemaking industry using grapes (Vitis vitaceae). The remaining product, called grape pomace, includes mainly grape skins and seeds, which are rich in flavonoids, a subgroup of the greater phenolic family. In the past, the high lignin content has limited the use of pomace use only to ruminant and rabbit feeds. The need for finding alternative means of enhancing animal health without the help of antibiotics has prompted nutritionists to re-examine the potential of using grape by-product extracts in monogastric feeds. Indeed, first research results are very promising. In pigs and poultry, various grape by-products have been shown to have strong antioxidant as well as significant anti-inflammatory and antimicrobial effects. In fact, some products are claimed as being able to reduce the need for supplemental vitamin E — a powerful antioxidant. However, further research is needed to determine optimum inclusion rate in commercial diets, especially in vitamin E replacement.
Grapes contain compounds with antioxidant activity similar to vitamin E. | Shaffandi, Dreamstime.com