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

Abstract

Naturally occurring plant compounds including tannins, saponins and essential oils are extensively assessed as natural alternatives to in-feed antibiotics. Tannins are a group of polyphenolic compounds that are widely present in plant region and possess various biological activities including antimicrobial, anti-parasitic, anti-viral, antioxidant, anti-inflammatory, immunomodulation, etc. Therefore, tannins are the major research subject in developing natural alternative to in-feed antibiotics. Strong protein affinity is the well-recognized property of plant tannins, which has successfully been applied to ruminant nutrition to decrease protein degradation in the rumen, and thereby improve protein utilization and animal production efficiency. Incorporations of tannin-containing forage in ruminant diets to control animal pasture bloat, intestinal parasite and pathogenic bacteria load are another 3 important applications of tannins in ruminant animals. Tannins have traditionally been regarded as "anti-nutritional factor" for monogastric animals and poultry, but recent researches have revealed some of them, when applied in appropriate manner, improved intestinal microbial ecosystem, enhanced gut health and hence increased productive performance. The applicability of plant tannins as an alternative to in-feed antibiotics depends on many factors that contribute to the great variability in their observed efficacies.

Keywords: Biological activities; Farm animal; In-feed antibiotics; Natural feed additives; Tannins.

Fig. 1

Model structures of (A) hydrolyzable tannins, (B) condensed tannins and (C) phlorotannins.

Fig. 2

Aggregation of Escherichia coli (strain 25922) cell incubated for 10 h with (A) 0 (Control) or (B) 200 μg/mL of condensed tannins of purple prairie clover (Dalea purpurea Vent.), and transmission electron micrographs of E. coli O157:H7 strain 3081 incubated for 24 h with (C) 0 or 50 μg/mL of (D) phlorotannins, (E) hydrolyzable tannins or (F) condensed tannins. Adapted from Wang et al., 2009, Wang et al., 2013 and Liu et al. (2013).

Fig. 3

Regression of bloat rate and proportion of sainfoin in herbage mass determined for beef steers (n = 12) grazing forage re-growth in 1999 and 2000 (adapted from Wang et al. (2006)).