Potential and challenges of tannins as an alternative to in-feed antibiotics for farm animal production

Huang, Qianqian; Liu, Xiuli; Zhao, Guoqi; Hu, Tianming; Wang, Yuxi

The potential of tannins as biological antioxidants has been indicated in many in vitro studies (Ho et al., 1999; Lin et al., 2001; Beninger and Hosfield, 2003; Barreira et al., 2008) . The in vivo antioxidant activities of tannins were also demonstrated in different animal tissues. Inclusion of forage containing CT improved antioxidant status of both cattle and sheep by increasing serum antioxidant activity (Dutta et al., 2012; Dey and De, 2014; Huang et al., 2015; Peng et al., 2016) . Quebracho tannins in lamb diets improved the antioxidant status of muscle (Luciano et al., 2011) , liver and plasma (L opez-Andr es et al., 2013) and enhanced meat color stability by delaying myoglobin oxidation during refrigerated storage (Luciano et al., 2009) . Given the fact that HT are degraded in the gastrointestinal tract before absorption whilst CT can not be degraded and absorbed from the digestive tract, it is not easily to explain how tannins as intact entities exert anti-oxidant activity within animal body. L opez-Andr es et al. (2013) found that quebracho tannins were not degraded or absorbed in the gastrointestinal tract, but increased the antioxidant capacity of liver and plasma in sheep, which demonstrated that CT may indirectly affect antioxidant status in animal tissues. The tannins-protein complexation has been shown to reduce but not eliminate the antioxidant activities of tannins (Riedl and Hagerman, 2001; Arts et al., 2002) . It has been speculated that dietary tannins may spare other nutritive antioxidants during digestive process or they may protect proteins, carbohydrates, and lipids in the digestive tract from oxidative damage during digestion (Marshall and Roberts, 1990) . However, the antioxidant mechanism of tannins in animal tissues is unknown. Further research in this area is needed, especially because enhancing antioxidant status is suggested to be one of the most benefits of feeding tannins to animal wellbeing and performance.