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

Unlike for ruminants, tannins have traditionally been considered as 'anti-nutritional' factors in monogastric nutrition with negative effects on feed intake, nutrient digestibility and production performance (Butler, 1992; Redondo et al., 2014) . Therefore, it is almost a common practice in feeding industry to minimize the use of tannin-containing feed in swine and poultry diets or to take measures to reduce their dietary concentrations if such feed are used. However, several recent reports showed that low concentrations of several tannin sources improved health status, nutrition and animal performance in monogastric farm animals Zotte and Cossu, 2009; Biagia et al., 2010; Brus et al., 2013; Star cevi c et al., 2015) . The mechanisms of growthpromoting effects of tannins in monogastric animal are much less understood compared with those in ruminants. Although there are some reports indicated that low concentrations of tannins increased feed intake and thus increased performance of monogastric animals, given the astringent nature of tannins, it seems not justified that this is through improving the palatability of feed. Information available to date seems to suggest that the growthpromoting action of tannins in monogastric animal relies on the balance between their negative effects on feed palatability and nutrient digestion through protein and enzyme complexation and positive effects on promoting the health status of intestinal ecosystem through their anti-microbial, anti-oxidant and antiinflammatory activities. The final impact of tannins on animal performance depends on the type of animals and their physiological status, feed, type of tannins and their concentrations in the diets. Compared with other domestic animals, pigs seem to be relatively resistant to tannins in the diets, and they are able to consume relatively high quantities of tannin-rich feedstuffs without presenting any toxic symptoms (Pinna et al., 2007) . This is likely due to parotid gland hypertrophy and secretion in the saliva of proline-rich proteins that bind and neutralize the toxic effects of tannins (Cappai et al., 2010 (Cappai et al., , 2014 . Compared to the vast sources of tannins for ruminants, sources of tannins used for monogastric animals are rather limited and so far only few have been studied and showed potential as feed additive (Table 2) .