Researchers at the Faculty of Veterinary Medicine of the University of Ghent in Belgium studied the use of tannins to control Salmonella Typhimurium infections in pigs (Van Parys A. et al, 2009). The aim of this study was to determine whether a hydrolysable tannin extract** of sweet chestnut wood has an inhibitory effect on Salmonella Typhimurium survival both in vitro and in vivo in pigs. In a first experiment, the minimal inhibitory concentration (MIC) of the tannin extract on 57 Salmonella Typhimurium isolates was determined. For all isolates, an MIC of 160-320 mug/ml was found. The second in vitro study revealed that Salmonella growth was strongly reduced using tannin extract concentrations of 25-50 mug/ml and nearly completely inhibited at a concentration of 100 mug/ml tannin extract. In an in vivo trial, two groups of six piglets, each group receiving feed with or without the addition of tannin extract (3 g/kg), were orally inoculated with 107 colony forming units of a Salmonella Typhimurium strain. The tannin extract had no effect on faecal excretion of Salmonella, and no differences in colonization of the intestines and internal organs were demonstrated in pigs euthanized at 4 days post-inoculation. The researchers concluded that the hydrolysable tannin extract used in this study showed strong action against Salmonella Typhimurium in vitro but not in vivo.
Effect on E. coli in steers
As shown in pigs and poultry, the use of tannins can have a significant effect on reducing bacteria. The Texas Agricultural Experiment Station in the US (2007) looked at the effect of tannins on the in vitro growth of Escherichia coli O157:H7 and in vivo growth of generic Escherichia coli excreted from steers. In the first experiment, the effect of commercially available chestnut and mimosa tannins in vitro was studied. Experiment 2
Tanin Sevnica: Tannin experts in Slovenia
Tanin Sevnica has been cooperating with nature since 1923. The company – based in Slovenia - produces extracts from chestnut and oak wood. With a staff of 130 people, the company produces extracts as tanning agents for vegetable leather tanning. From the extracted wood also other products are produced such as Furfural and Sodium Acetate. Since the beginningog the 90s, the company started with the production of natural extracts from a sweet chestnut and oak woods for the human and animal nutrition. Around 5% of tannins for animal nutrition that Tanin Sevnica produces are sold in Slovenia, the rest goes to other EU member, Asia, Africa and the Middle East.
was an in vivo study and looked at the recovery of Escherichia coli O157:H7 or generic fecal E. coli. In experiment 1, the mean growth rate of E. coli O157:H7, determined via the measurement of optical density at 600 nm during anaerobic culture in tryptic soy broth at 37oC, was reduced (P < 0.05) with as little as 400 microg of either tannin extract per ml of culture fluid. The addition of 200, 400, 600, 800, and 1,200 microg of tannins per ml significantly reduced the specific bacterial growth rate when compared with the non-tannin control. The specific growth rate decreased with increasing dose levels up to 800 microg of tannins per ml. Bacterial growth inhibition effects in chestnut tannins were less pronounced than in mimosa tannins. Chestnut tannin extract addition ranged from 0 to 1,200 microg/ml, and a linear effect was observed in cultures incubated for 6 h against the recovery of viable cells, determined via the plating of each strain onto MacConkey agar, of E. coli O157:H7 strains 933 and 86-24, but not against strain 6058. Similar tests with mimosa tannin extract showed a linear effect against the recovery of E. coli O157:H7 strain 933 only. The bactericidal effect observed in cultures incubated for 24 h with the tannin preparations was similar, although it was less than that observed from cultures incubated for 6 h. When chestnut tannins (15 g of tannins per day) were infused intraruminally to steers fed a Bermuda grass hay diet in experiment 2, fecal E. coli shedding was lower on days 3, 12, and 15 when compared with animals that were fed a similar diet without tannin supplementation. In this study, dietary levels and sources of tannins potentially reduced the shedding of E. coli from the gastrointestinal tract.
Rabbit meat quality
An Italian study (2009) showed some interesting results regarding the supplementation of tannins and its effect on meat quality, fatty acid profile and lipid stability in broiler rabbits. A total of 72 commercial hybrid rabbits (mean body weight 740 g, 32-days-old) were fed for 49 days with three diets containing 0%, 0.5% and 1.0% of a commercial chestnut wood extract***, respectively. Eight rabbits per group were slaughtered at 12 weeks of age and at 24 h post-mortem pH and colour were measured on the carcass. Moreover, both sides of m. longissimus thoracis (LT) were dissected. Left side was used for cooking losses whereas the other side was used for the determination of fatty acid profile and lipid oxidation. The researchers found no differences in pH, colour and cooking losses, as well as the fatty acid profile of LT muscle and its relative health indexes. Concerning the antioxidant effect, the tannin extract showed a positive and significant effect at the inclusion level of 0.5%. In conclusion, the tannin extract has no undesirable side effects on the meat quality of rabbits, although further studies will be necessary to find the optimal diet inclusion level of the tannin extract to elicit a stronger antioxidant effect in the rabbit meat.
Tannins can have beneficial effects on the digestion and hence animal performance when they are incorporated in animal diets. However, the great diversity of the results presented in different papers, related to the chemical composition and source of tannins, specific reaction of different animal species to tannins in feeds or supplements and to the dose-response of animals indicate the necessity of further investigations to have more data on the mode of action and potency of these compounds applied in animal diets.
* SCT, Sweet Chestnut Tannin. ** Globatan®, *** Silva Feed ENC®