Digestibility and effects of condensed tannins on digestion of sulla ( Hedysarum coronarium ) when fed to sheep

Sulla ( Hedysarum coronarium ) is a short‐lived perennial legume with an erect growth habit which is grown as a fodder crop in Mediterranean regions but is not common in New Zealand agriculture. Recent experimental work has shown potential benefits of sulla for reducing the impact and numbers of intestinal nematodes in sheep and possible benefits for wool production, so that a feeding trial was undertaken to determine its digestibility. Twelve sheep aged about 6 months were held in metabolism crates and fed sulla as a sole diet for the 20‐day experimental period. Sulla contains condensed tannins (CT) so that one group of 6 sheep were given twice‐daily oral drenches of polyethylene glycol (PEG) to bind with and deactivate the CT (PEG group) enabling a comparison with the undrenched Tannin group. The dry matter (DM) content of the sulla was 15.5%, comprising (DM basis) 33% leaf, 41% stem, and 26% flower, and all portions of the plant were eaten. The DM contained about 7.2% CT and 3.0% nitrogen (N). DM intakes averaged 1160 g/day and DM digestibility was lower in Tannin animals (70.5%) than those given PEG (72.5%; P = 0.015). Condensed tannin substantially reduced N digestibility (63.1%) relative to those given PEG (77.1%; P < 0.001) and this was associated with a reduction in rumen ammonia concentration ((mol/ ml) in Tannin (155) versus PEG (259) animals. Plasma urea concentrations (umol/ml) were also lower ( P < 0.001) in Tannin sheep than in those given PEG (7.4 vs 8.8) which suggests that the CT affected the digestion, absorption, and metabolism of nutrients.