Anti-Inflammatory and Antioxidative Phytogenic Substances against Secret Killers in Poultry: Current Status and Prospects

Simple Summary Chronic stress and inflammation, known also as "secret killers" in animals, can lead to lipid peroxidation, protein oxidation and nitration, DNA damage, and finally apoptosis. This is due to an imbalance between free radical generation and endogenous antioxidant defense, which in turn possess detrimental impacts on the health and performance of animals. In this review, we discuss the mechanistic pathways of oxidative stress and inflammation associated with the main secret killers in poultry, namely heat stress, dysbiosis, leaky gut syndrome, and mycotoxins. Additionally, we shed light on the potential use, challenges, and future prospects of phytogenic bioactive substances in mitigating oxidative stress and inflammation in poultry. Chronic stress is recognized as a secret killer in poultry. It is associated with systemic inflammation due to cytokine release, dysbiosis, and the so-called leaky gut syndrome, which mainly results from oxidative stress reactions that damage the barrier function of the cells lining the gut wall. Poultry, especially the genetically selected broiler breeds, frequently suffer from these chronic stress symptoms when exposed to multiple stressors in their growing environments. Since oxidative stress reactions and inflammatory damages are multi-stage and long-term processes, overshooting immune reactions and their down-stream effects also negatively affect the animal's microbiota, and finally impair its performance and commercial value. Means to counteract oxidative stress in poultry and other animals are, therefore, highly welcome. Many phytogenic substances, including flavonoids and phenolic compounds, are known to exert anti-inflammatory and antioxidant effects. In this review, firstly, the main stressors in poultry, such as heat stress, mycotoxins, dysbiosis and diets that contain oxidized lipids that trigger oxidative stress and inflammation, are discussed, along with the key transcription factors involved in the related signal transduction pathways. Secondly, the most promising phytogenic substances and their current applications to ameliorate oxidative stress and inflammation in poultry are highlighted.