Table 1.

In vivo and in vitro effects of tannin-rich plant extracts on performance and health of poultry.

Tannin source and type	Major findings		Doses (g/kg)	References
In vivo effect of tannin-rich plant extracts on performance and health of poultry
	Performance effects	Health effects
Muscadine pomace (HT and flavonoid; Vitis rotundifolia)	Birds given 50 g/kg had poorer average live weight. Extracts at 5 and 20 g/kg improved BWG after challenge with CP in a NE model.	Treated birds showed increased resistance to coccidia infection and lower lesion scores after challenge with coccidia (Eimeria spp.). Extracts at 5 and 20 g/kg reduced mortality and lesion scores using an established model of NE.	5, 20, and 50	[33]
Chestnut (HT; Castanea sativa)	Chestnut extract did not influence feed digestibility, carcass quality, or N balance and showed a positive influence on growth performance up to 2 g/kg.	Carcass analysis showed no gross lesions in organs and no significant differences in thigh and breast composition among groups.	1.5, 2, and 2.5	[34]
Chestnut (HT)	—	Chestnut extract reduced the counts of CP and macroscopic gut lesions in a NE model challenged with coccidia and CP. Results were more pronounced at higher tannins doses.	1.5, 3, 5, and 12	[35]
Quebracho (CT; Schinopsis lorentzii)	Quebracho supplementation significantly increased BWG and intestinal V : C ratio.	Birds challenged with coccidia (Eimeria spp.) and treated with quebracho extract showed decreased oocyst excretion. No differences in mortality or intestinal lesion were observed.	100	[36]
Grape pomace (CT)	No negative effects on growth performance, digestive organ sizes, or protein digestibility were detected at levels up to 60 g/kg to 42 d of age.	Antioxidant activities in diet, excreta, ileal content, and breast muscle were increased by grape pomace concentrate.	15, 30, and 60	[37]
Grapeseed (CT; Vitis vinifera)	Inclusion of grapeseed extract up to 3.6 g/kg did not affect growth performance and increased protein and polyphenol digestibility.	Grapeseed extract caused a significant increase of antioxidant activity in diet and excreta.	0.6, 1.8, and 3.6	[38]
Grapeseed, mimosa (CT), and cranberry (CT + HT)	Mimosa extract reduced BWG and FCR while cranberry reduced feed digestibility.	Mimosa and cranberry supplements decreased minor VFA concentration, which is probably associated with inhibition of microbiota activity.	373, 258, and 24, respectively	[39]
Grape pomace and grapeseed (CT)	Grapeseed diet showed decreased BWG. Both extracts reduced intestinal crypt depth and increased muscular thickness.	Both extracts decreased the counts of Clostridium in ileum but these were increased in cecum. Only grapeseed extract showed antimicrobial activity against CP.	60 and 7.2, respectively	[40]
Grape pomace (CT)	No differences in BWG or FCR were observed. Birds fed with grape pomace diets had a higher content of meat polyunsaturated fatty acids.	Grape pomace added up to 100 g/kg prevented meat lipid oxidation similar to vitamin E.	50 and 100	[41]
Quercetin (flavonoid)	FCR decreased as quercetin level increased. Laying rate was maximized by supplementation of quercetin at 0.2 g/kg. No significant effect on egg quality was observed.	Microbial population of aerobes and coliforms decreased at higher levels of quercetin, while bifidobacteria increased. Antioxidant activity in liver was increased by quercetin.	0.2 to 0.6	[42]
Tannin source and type	Major findings		Doses (mg/mL)	References
In vitro effect of tannin-rich plant extracts on CP and other poultry pathogens
Chestnut (HT) and quebracho (CT)	CP types A, B, C, D, and E growth was inhibited in a dose-dependent manner in the presence of all tannins extracts. Quebracho tannins showed partial bactericidal activity, whereas chestnut tannin activity was stronger. Both tannins reduced alpha toxin lecithinase activity and epsilon toxin cytotoxicity.		0.03 to 8	[32]
Blackberry, cranberry (CT + HT), chestnut (HT), mimosa, quebracho, and sorghum (CT)	Tannins exhibited a variable degree of inhibition of Campylobacter jejuni depending on source and medium composition. Inhibitory activity of CT extracts but not HT was mitigated by casamino acid supplementation, likely because the added amino acids saturated the binding potential of CT.		100	[43]
Chestnut, tara, sumach (HT), quebracho, Calliandra (CT), green tea, and acacia (flavonoid)	Despite their structural diversity, all tested tannins showed antimicrobial effects against Salmonella Typhimurium either in liquid culture or in the diffusion assay. Tara extracts effectively reduced the counts of Salmonella Typhimurium at low doses (1 mg/mL).		1 to 6	[44]
Chestnut (HT) and quebracho (CT)	All compounds showed extracellular antiviral effect against both avian reovirus and avian metapneumovirus at concentrations ranging from 25 to 66 μg/mL. Quebracho extract also had intracellular activity.		0.01 to 0.15	[45]

CP: C. perfringens; BWG: body weight gain; HT: hydrolyzable tannins; CT: condensed tannins; FI: feed intake; FCR: food conversion rate; NE: necrotic enteritis.