Effect of condensed tannins on the production of wool and on its processing characteristics in sheep grazing Lotus corniculatus

Abstract

The effect of condensed tannins (CT) in Lotus corniculatus upon voluntary feed intake (VFI), concentration of rumen and plasma metabolites, production of wool, and wool processing characteristics was measured in grazing ewes restricted to maintenance feeding for 125 days during summer. A rotational grazing system with restricted feed allowance with 40 mixed aged dry ewes (54±1·0 kg) was used. Half of the ewes were selected randomly for twice-daily oral polyethylene glycol (PEG; MW 3500) supplementation (CT-inactivated), with the remainder being CT-acting animals. Measurements of the diet selected, VFI, wool production, and wool processing characteristics were made. The concentration of ammonia in rumen fluid and the concentrations of methionine, cysteine, and urea in blood plasma were also measured. The diet selected contained 32 g total nitrogen (N) and 28 g total CT/kg dry matter (DM) and had an in vitro organic matter digestibility of 0·70. Action of CT reduced rumen ammonia concentration (256 v. 302 mg N/L), reduced blood plasma urea concentration (7·3 v. 8·9 µM), and increased blood plasma cysteine concentration (30 v. 27 µM) compared with sheep receiving PEG supplementation. CT had no effect on VFI but increased clean fleece weight (2·53 v. 2·28 kg/ewe) and staple length (7·7 v. 6·9 cm), but did not affect liveweight gain (54 v 67 g/day). The CT reduced dag weight and tended to reduce wool yellowness relative to sheep receiving PEG. There were no signifiant effects of CT on fibre diameter, staple strength, bulk density, and wool resilience. It was concluded that action of CT in sheep fed L. corniculatus reduced the degradation of forage protein in the rumen and the principal effect of this was to increase the efficiency of wool production, with more wool being produced at the same feed intake and the wool being of reduced yellowness.