ISSUE FOCUS FEED & ADDITIVE MAGAZINE September 2023 31 ductive 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). Over-
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