Intake, digestibility, urinary excretion of purine derivatives and growth by sheep given fresh, air-dried or polyethylene glycol-treated foliage of Acacia cyanophylla Lindl.

Effects of air-drying or spraying Acacia cyanophylla Lindl. leaves with pol yethylene glycol (mol. wt 4000; PEG) upon aqueous methanol-extractable vani llin-HCl condensed tannins (CT) level were studied in Barbarine and Queue F ine de l'Ouest sheep. Drying was under sun or shade for 2, 7, 14 or 28 days and PEG treatment (PEG/CT ratios: 0.5, 1.0, 2.0 or 4.0). Sun-drying was sl ightly more efficient in reducing CT levels in acacia foliage than shade-dr ying (29.4 and 20.4% reduction in 48 h, 38.7 and 33.8% in 28 days). PEG tre atment of freshly cut material at a rate of 0.5, 2 and 4 g g(-1) CT reduced the CT content of acacia foliage by 29.0, 51.8 and 55.5%. Using fresh, fie ld-dried and PEG-treated acacia foliage harvested at the same time, digesti bility and growth trials were performed with five adult rams (total faecal collection, 28 days) and six growing ii-month old female lambs per treatmen t. Animals received daily acacia ad libitum and 400 g barley per head. Fres h leaves of acacia were field-dried for 14 days, or sprayed with PEG soluti on at a rate PEG/CT of 2.0 at the time of feeding. Acacia and total diet dr y matter (DM) intakes by adult and growing sheep were similar across experi mental diets, Fresh and dried acacia had the same low nutritive value. Shee p on PEG-containing diet gained more weight (p < 0.05) than those on fresh or dried acacia (95 g day(-1) vs. 69 or 73 g day(-1), respectively). Dietar y crude protein and neutral detergent fibre (NDF) digestibilities were incr eased by PEG treatment when compared with fresh acacia (72.8 vs. 38.7% and 48.3 vs. 39.9%, respectively). In comparison with fresh or dried acacia, PE G treatment increased nitrogen retention (p < 0.05), the urinary excretion of purine derivatives (PD) by 17% (p < 0.05), suggesting an increase in out flow of microbial protein from the rumen. It is concluded that PEG may be u sed to improve the nutritive value of A. cyanophylla foliage. However, the reduced extractable CT induced by air-drying may simply reflect a reduced s olubility of CT-protein complexes. (C) 1999 Elsevier Science B.V. All right s reserved.