Polyphenols as a natural strategy to effectively control oxidative stress in layers

Stress affects the performance, health status and thus economic profitability of layers during their egg production cycle. Oxidizing agents are formed throughout the body exceeding the hen’s antioxidant capacity. Such oxidative stress leads to a suboptimal functioning of vital organs, lower egg production or -quality, as well as higher susceptibility to diseases. Therefore, productive hens are often in need of preventive tools such as highly effective bioactive antioxidants added sufficiently to their diet, for an adequate level of protection.

OXIDATIVE STRESS, AN IMPORTANT METABOLIC CHALLENGE
Oxidative stress is a major and still underestimated issue in animal production leading to significant performance losses. It is caused by multiple factors such as
• antibiotic treatments
• climatic stress, e.g. heat stress
• high animal stocking densities
• pathogenic pressure (low hygiene)
• animal handling
• feed quality and -transitioning
• ventilation
• induced molting

Also a high metabolic activity, linked to intensive production systems, represents a key disposal factor. When too much of these stressors impact the animal, an imbalance occurs between the formation of unstable oxidants (i.e. free radicals) and the biological capacity of body cells to detoxify them. Thus, during such challenging conditions, the animal fails to produce sufficient endogenous antioxidants itself. An overload of free radicals – mainly Reactive Oxygen Species (ROS) – is generated in vivo. An important source of these unstable intermediates is the cell’s mitochondria as these are characterized by an intense oxidative metabolism (i.e. aerobic respiration), and their functioning is very sensitive to ROS-induced damage. Excess radicals attack and damage macromolecules in vital constituents of all types of body cells, such as the cell membrane (i.e. phospholipid peroxidation), mitochondria and the genetic material. Such oxidative biological injuries provoke an impaired integrity, functioning or even death of cells, resulting in inflammation which further enhances oxidative stress. Oxidative damage on a cellular level affects several tissues and eventually the whole body, i.e. systemic level.

HEAT STRESS, A KEY DRIVER FOR OXIDATIVE STRESS ALSO IN LAYERS
Similar to other farmed livestock species, laying hens face cellular oxidative stress during their productive life cycle. Especially environmental heat stress has shown to be one of the most crucial drivers, next to an intense metabolic rate of highly productive genetic breeds. Just like pigs, poultry have a low capacity to dissipate excess body heat to the environment, as they lack the ability to sweat. This makes them very sensitive to thermal stress, and consequently a state of oxidative stress. In particular chronic heat stress increases the formation of ROS to a problematic level, by promoting intestinal inflammation and –ischemia (i.e. a reduced blood flow of nutrients and oxygen to the intestines). It also reduces the animal’s antioxidant response of gut epithelial cells, including reductions in the gene expression of endogenous antioxidant enzymes. The main way for layers to cool down their body or thermoregulate, is by evaporative cooling via panting (i.e. hyperventilation). But this in fact involves a high production of ROS and thus further enlarges the ‘antioxidant gap’. All these intrinsic processes under persistent heat conditions will favor the manifesting of oxidative stress, tissue damage and consequently metabolic energy losses in layers.

The redox imbalance that oxidative stress encompasses, affects the oxidative status of laying hens’ different corporal tissues, like their intestines, liver, bones and reproductive tract. An excess of ROS is a burden that increases their requirements for body maintenance, as the repair of oxidative injuries to biological compounds demands a lot of endogenous resources like cellular energy and proteins. Inevitably, such a metabolic drainage will undermine the genetic potential of layers and thus restrict their overall egg output.

KEY CRITERIA FOR BIOACTIVE DIETARY ANTIOXIDANTS
A body state of oxidative stress requires extra dietary supplementation of more effective bioactive antioxidants, thus beyond Vitamin E, C, A or Selenium. Distinct classes of polyphenols originating from specific botanical sources have proven to be powerful and versatile antioxidant solutions. Not all polyphenolic types are as suitable or efficacious in mitigating the stress level. For polyphenols to be truly impactful in vivo antioxidants, they require particular characteristics. First, they should have a moderate chain length or molecular weight to guarantee an adequate gut absorption. Secondly, a high water solubility is of utmost importance to also provide intra-cellular protection of key biological structures. Moreover, a sufficiently low redox potential value is a crucial chemical property for an effective electron donation to different radical species (incl. used antioxidants like oxidized Vit. E). Overall, selected polyphenols should dispose of multiple antioxidant mechanisms such as a
1. broad-spectrum neutralization of different radical types (i.e. scavenging power),
2. significant recycling of oxidized in vivo antioxidants (i.e. regenerating power),
3. active stimulation of the endogenous antioxidant system (i.e. upregulating power)

Dietary polyphenols of such a versatile nature will reduce oxidative body damage to a significant level. Firstly, this will allow a higher integrity of cells or in other words save endogenous resources. Secondly, such diverse antioxidant modes of protection against radicals, will result in a better or more efficient functioning of mitochondria in producing metabolic energy (ATP). By doing so, much more nutrients will become available for production and will not be redirected or lost to the oxidative repair of injured cells for body maintenance. Therefore, under stressful field conditions, such polyphenols will keep the animal’s metabolism in a balanced state of (energy) homeostasis, by efficiently closing the ‘antioxidant gap’.

IMPROVED EGG PRODUCTION
In this article, an interesting layer trial is described. A synergistic and concentrated blend of carefully selected natural extracts – fully complying with above polyphenolic criteria – was evaluated as a possible antioxidant solution in a practical research facility (Brazil, 2022). A total of 192 Hisex Brown^® phase 2 laying hens of 55 weeks old, were kept for 4 subperiods of each 30-days long in the same house. All birds were randomly assigned to 3 treatment groups (Control, 0.5 and 1 kg/t ELIFE^® antioxidant supplementation). This way, all groups were standardized on equal body weight and egg production rate at the start of the trial. All birds had free access to water and feed, being a standard commercial corn-soy based diet.

Throughout the entire experiment, laying rate was consistently higher for both antioxidant dosages compared to control. Overall, over the 16 weeks of trial, both supplementation groups achieved a significant improvement (p < 0.05) of resp. 3.5 and 4.0 percentage points compared to the control group (Figure 1). This translated into resp. 4.0 and 4.5 eggs more per hen over the entire test period (or resp. 35 and 41 eggs more per 1000 hens per day). Therefore, the phytogenic blend improved persistency of the hens’ laying curve (i.e. prolonged their high egg producion rate during phase 2 of lay).

Due to an additional improvement in average egg weight, both supplemented groups yielded a higher Egg Mass Production versus control during the entire experiment (Figure 2). Overall, across the total evaluation period, this resulted in a significant (p < 0.05) increase in EMP of resp. 5.8 and 5.7 % compared to the control group.

Moreover, the balanced polyphenolic mixture enabled a more efficient egg production during phase 2 of lay, by reducing the feed conversion ratio. Over the entire trial, hens from the 0.5 and 1 kg/t ELIFE^® treatment groups showed a significant (p < 0.05) reduction of resp. 10 and 13 points versus hens from the control (Figure 3). All this, presumably, by strongly alleviating the level of cellular oxidative stress and thus body tissue damage within these high-performing hens (i.e. fewer nutrient losses).

BENEFITS BEYOND LAYING PERFORMANCE
Next to hindering egg production, oxidative stress also leads to a suboptimal egg quality. This was illustrated in the same trial by an improved overall egg quality, especially at the highest ELIFE^® dosage. Firstly, eggshell strength was significantly (p < 0.05) improved (Figure 4). This most probably can be explained by a better neutralization of inflammation-inducing ROS, which are omnipresent in the gut. In other words, ELIFE^® allowed for a higher integrity of epithelial cells on the intestinal villi, and thus improved the absorption of dietary calcium. Secondly, the level of yolk Vit. E (antioxidant capacity) was drastically increased by 53 % (p = 0.1208), thus also contributing to a higher nutritive value for consumption (Figure 5). Finally, at this same dosage of 1 kg/t, the sampled eggs displayed a significant (p < 0.05) reduction in yolk TBARS level, which indicated less lipid peroxidation or an improved shelf life (Figure 6). This last finding was in line with the yolk ROS level, which was significantly (p < 0.05) reduced by 49.1 % at the 1 kg/t ELIFE^® antioxidant dosage.

CONCLUSIONS
The body tissues of adult layers, especially the digestive and reproductive organs, are considerably affected under conditions of oxidative stress, induced by factors such as heat stress or a high metabolic rate. This leads to several metabolic losses in the laying hen and thus a suboptimal egg performance for farmers, but also an impaired egg quality for processors and end consumers. However, treating the diet of hens with ELIFE^® natural antioxidant blend during phase 2 of lay, has shown to maximize productivity and thus increase persistency of egg production significantly. Moreover, average egg weight and consequently egg mass production were improved as well. This as a result of controlling the level of oxidative cell damage (e.g. energy expenditures) throughout the hen’s entire body, incl. its reproductive tract. It was also empirically proven that dietary supplementation with ELIFE^® significantly reduced FCR (feed to egg mass), confirming a lowered requirement for body maintenance. Such a better redox balance was backed by a lower oxidative status and higher antioxidant capacity of eggs’ yolk. By also preserving the integrity of the gut’s epithelium as an antioxidant, ELIFE^® additionally supported a higher nutrient absorption like calcium, resulting in a significantly improved eggshell strength. Finally, such promising results also invite to evaluate the polyphenolic concept in the breeder chickens application.

References are available upon request via [email protected]

About Steven Beckers
Steven Beckers is a poultry nutritionist with a Master’s degree in Applied Bio-Sciences Engineering from the University of Leuven (Belgium). Since 2019, Steven is a Global Product Manager of multiple specialty feed additives at Impextraco. Here he provides technical support to customers and end users, to help establish innovative concepts in different agricultural markets. He is devoted to maximizing animal health and performance, by correctly advising and optimizing the application of value-added products.