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

Hydrolyzable tannins from chestnut (Castanea sativa Mill.) have recently been assessed as feed additive for monogastric food producing animals. Although in vitro studies showed strong activities against parasites and pathogens residing in animal digestive tract (Chung et al., 1998; Athanasiadou et al., 2000; Butter et al., 2001) , the in vivo assessments have yielded inconsistent results for animal performance. At the concentrations from 0.11% to 0.45% in swine diets, it was found that chestnut HT improved feed efficiency, tended to increase viable counts of Lactobacilli in the jejunum and reduced caecal concentrations of ammonia, iso-butyric, and isovaleric acid, but had no effect on bacterial caecal counts, faecal excretion of Salmonella or colonization of the intestines (Biagia et al., 2010; Parys et al., 2010) . However, increasing concentration from 0.71% to 1.5% reduced feed efficiency although feed intake, growth and carcass weight were not affected (Bee et al., 2016) . Stukelj et al. (2010) reported that chestnut HT at the level of 0.15% in combination with 0.15% of a mixture of acids had no effects on health status or growth performance of pigs whereas Brus et al. (2013) found that 0.19% of it in combination with 0.16% of a mixture of acids increased growth performance, increased lactic acid bacteria and reduced E. coli populations in the intestines. Schiavone et al. (2008) evaluated the effects of adding 0.15%, 0.20% and 0.25% of chestnut tannin product (77.8% HT) on growth performances of broiler chicks. The results showed that inclusion of up to 0.20% of chest nut tannin increased daily feed intake and average daily gain. However, increasing its concentration to 0.25% seemed to lead to negative effects as all the measured parameters were the lowest. Jamroz et al. (2009) assessed the effects of dietary addition of 0.025%, 0.05% and 0.1% of sweet chestnut tannins on the performance, intestinal microbial populations and histological characteristics of intestine wall in chickens. Their results showed that tannin supplementation had no effects on feed conversion and carcass quality, but tannin at 0.1% reduced final body weight and slowed down the proliferation rate in the mother-cell zone. E. coli and coliform bacteria in the small intestines of 28-d-old chickens were also reduced at the tannin levels of 0.05% to 0.1%. In another study, Rezar and Salobir (2014) found that addition of 0.07% and 0.2% of the same tannin product (0.05% and 0.1% HT) did not affect broiler growth performance or the organic matter, crude protein, crude ash, calcium and phosphorus balance and utilization, but increased dry matter content of excreta. In a challenged study, Tosi et al. (2013) reported that chestnut HT at the dietary concentrations of 0.71% and 1.5% reduced Clostridium perfringens (Eimeria tenella, Eimeria acervulina, Eimeria maxima) in the gut of broiler chicken orally challenged with these coccidia.