ABSTRACT:In 3 preliminary trials, the effect of a dietary addition with 0.5% of a chestnut tannin extract, containing approximately 55% hydrolysable tannins, was examined on mortality after weaning. The tannin-enriched diet was fed to the does and their litters from 22 days of lactation. After weaning (day 29), young rabbits did not change dietary treatment and remained on the control diet or the tannin-enriched diet, respectively. In total 1217 rabbits were considered, about half of whom were fed the tannin-enriched diet. Mortality reached 17.1% and 7.7% (trial 1, P=0.054), 17.2 and 18.2% (trail 2, NS) and 29.0% and 9.9% (trial 3, P<0.001) in controls and tannin-fed rabbits, respectively. The autopsy on 6 control rabbits revealed typical symptoms of rabbit epizootic enteropathy with a predominance of Clostridium spiroforme. Weight gain was determined only in trial 3 and was significantly higher in tannin-fed rabbits (average weight at 57 d of age: 1893 and 2005 g, respectively; P<0.01). Some hypotheses are formulated to explain these preliminary results, but they still have to be verified.

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To evaluate the possible interaction between tannins and the activity of exogenous feed enzymes, the effect of tannin supplementation on added phytase efficiency in pigs was studied. An extract of sweet chestnut (Castanea sativa Mill.) wood was used as the source of tannins. Thirty-six pigs were divided into five groups: control (no supplement), Phy (550 PU/kg, 0 g tannins), Phy+Tl (550 PU/kg, 1.1 g tannins/ kg), Phy+T2 (550 PU/kg, 2.2 g tannins/kg) and Phy+T3 (550 PU/kg, 4.5 g tannins/kg). The results proved that phytase supplementation in the Phy group significantly increased apparent P digestibility and balance, Ca balance, serum inorganic P concentration, significantly reduced serum Ca concentration, numerically improved apparent nitrogen digestibility and significantly increased the N balance. Compared with the Phy group, the addition of tannins significantly reduced apparent protein digestibility. The apparent crude ash digestibility in the Phy+T3 group was also reduced (PO.08). The utilization of phosphorus and calcium was unaffected by tannin supplementation. In conclusion, the applied concentrations of tannins did not reduce the phosphorus-related efficiency of phytase action in growing pigs.

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