Phytogenic feed additives: Keeping oxidative stress down with plant extracts
The rising global population comes with an increasing demand for food, with animal protein playing an increasingly important role as source of protein. Poultry meat production is world-wide the fastest growing meat sector, and estimated to increase by 40% during the next five years, mainly in (sub)-tropical areas. Modern poultry breeds have a high and continuously increasing potential for fast growth, high feed efficiency and extended laying persistency under a wide variety of environmental conditions. However, selection for improved production was indicated to negatively influence adaptive immunity, increase the incidence of metabolic diseases and make birds more susceptible to (heat) stress. Optimized bird management and nutrition can help to alleviate oxidative stress. This article reviews the antioxidant values of phytogenic feed additives in poultry.
Oxidative stress - what is it and why does it occur?
Oxidative reactions are the basis for metabolic processes in the cell, needed to generate energy. During cellular metabolism reactive oxygen species (ROS) are produced. Due to their reactive nature, ROS can damage cell walls, like stones hitting and breaching the fortified walls of a medieval city.
These ROS can be neutralized by endogenous antioxidant mechanisms and radical scavengers like polyphenols. An imbalance of this system, also called oxidative stress, especially due to increased oxidative processes, can then lead to cell and tissue damage (e.g. damage of liver cells, mucosal cells). Oxidative stress can be caused by different factors, originating from nutritional, environmental or internal conditions. Table 1 summarizes factors that increase oxidative stress.
Table 1: Stress conditions increasing oxidative stress in birds
|- Oxidized dietary fat|
|Deficiencies and minerals|
|- Vitamin C, E|
|- Se, Mn, Zn|
|- High fermentable crude protein|
|- High non-starch polysaccharides|
|Air quality (NH 3 and CO 2 concentration)|
|Internal||Diseases (bacterial, viral, parasites)|
|Increased performance level|
Oxidative stress in poultry
The gut is one of the most important organs that affects poultry performance and health. As gut challenges affect bird performance, nutrition and management are focused on a fast gut development after hatch, and maintenance of a healthy and intact gut. Maintaining intestinal barrier functions is important for preventing pathogens passing from the intestinal barrier, which is the first line of defense. Reactive oxygen species from lipid peroxidation in the enterocytes cause a significant reduction of barrier function and reduce gut health overall. Moreover, it affects nutrient uptake and cell turnover. It was shown that the addition of thyme essential oils to broiler diets reduces lipid peroxidation and improves intestinal integrity (measured as trans epithelial electrical resistance) as indicated in Figure 1.
Lipid and protein oxidation have been recognized to have a large impact on membrane stability and hence, meat quality. A pro-oxidative environment initiated before (e.g. stress before slaughter) and after animal slaughter leads to increased oxidative reactions during handling, processing and storage of poultry meat. This negatively affects meat quality parameters like post mortem pH decline, drip loss or juiciness.
What does that mean to poultry production?
Several nutritional strategies are available to alleviate oxidative stress and thus, enhancing health and welfare status of poultry flocks. The physical form of the diet, feed composition as well as the quality of single feed ingredients used are major tools, not only to control, but also to improve poultry health.
Adding synthetic or natural antioxidants to poultry diets, limiting lipid peroxidation in feed, is common practice, especially in case of high dietary levels of polyunsaturated fatty acids (PUFA). Supporting the bird's antioxidant system by adding selenium, manganese or Vitamin C or E are well-recognised. However, evidence on the beneficial effects due to application of natural phytogenic additives as antioxidants, is increasing. This is something we have already known from human nutrition for years. Diets rich in vegetables and fruits have shown to increase intake of antioxidants and thereby reduce oxidative stress and inflammation, thus minimizing the risk to develop cardiovascular diseases.
Phytogenic feed additives (PFA) contain various biologically active substances like essential oils, pungent and bitter substances, tannins and saponins and represent a natural and innovative solution for today's challenges in livestock production. Phytogenic feed additives like Biostrong® 510 (Delacon Biotechnik GmbH, Austria) show clear potential to reduce fatty acid oxidation. Moreover, it reduces the level of ammonia in the air, limiting oxidative stress to the cells.
Figure 1: Biostrong® 510 significantly increases Superoxidase dismutase (SOD) and Glutathion peroxidase (GSH-PX) activity in broilers (Source: Delacon research)
Figure 2: Thymol significantly reduces fatty acid oxidation (MDA) and improves electrical resistance (TER) of the gut in broilers (Source: Placha et al. 2014)
Additional to the effects on antioxidant enzymes, essential oils with phenolic structures are able to directly scavenge ROS, reducing the risk for some diseases like cardiovascular disease, liver dysfunction and immune system decline. With an increasing number of phenolic structures in essential oils, the antioxidant capacity increases (Figure 3). Examples of essential oils with a high content of phenolic structures are thymol, carvacrol, eugenol and cinnamaldehyde. Recent literature indicates a higher efficacy of such natural anti-oxidants compared to the normally used synthetic antioxidants or vitamin E.
Figure 3: High phenolic content provides high antioxidant capacity (source: Cai et al. 2004)
Challenges in poultry production, like oxidative stress, emphasize the importance of nutritional expertise and optimum feeding management in order to allow birds to fully meet their genetic potential. High quality phytogenic products like Biostrong® 510, containing essential oils, herbs and spices, have shown to significantly improve performance in poultry efficiency in a natural though proven way. Additionally, they exert antioxidant effects, which seem to be a very important feature of a valuable phytogenic feed additive. Moreover, the stimulation of antioxidant effects could be another criterion to make a final selection in terms of health promoting feed additives. Natural, standardized, and scientifically and commercially proven phytogenic products offer vast potential for professional and efficient animal production. Due to their content of an infinite variety of active ingredients, phytogenic substances represent one of the most interesting and important classes of current and future feed additives.
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Article made possible through the contribution of Dr. Jan Dirk van der Klis, Leopold Jungbauer and Delacon