Benefit from the association of small amounts of tannin-rich shrub foliage (Acacia cyanophylla Lindl.) with soya bean meal given as supplements to Barbarine sheep fed on oaten hay

Two trials were conducted to test the hypotheses that (i) feeding small amount of a tanniniferous shrub foliage (Acacia cyanophylla Lindl., acacia) increases the proportion of rumen undegradable protein, and consequently benefits growth performance in Barbarine lamb; and (ii) such positive effect depends on the timing of feeding tannin source (i.e. acacia) relative to protein source (soya bean meal, SBM). Total (TT) and condensed tannin (CT) concentrations in air-dried acacia leaves used in this study averaged 29 g tannic acid and 48 g leucocyanidin equivalents per kg dry matter (DM), respectively. In trial 1, rumen fistulated ewes received oaten hay (hay) ad libitum and 200 g SBM (D1), D1 and 100 g acacia fed with the SBM (D2, mixed strategy) or as D2, but the SBM fed 1 h later than acacia when acacia was consumed completely (D3, sequential strategy). Hay intake, diet digestibility, rumen fermentation parameters (pH, ammonia nitrogen (NH3-N) and total volatile fatty acids) and in situ degradation of SBM nitrogen were similar between D1 and D2 (P > 0.05). However, the sequential strategy (D3) resulted in efficient use of N as reflected by the decrease of crude protein digestibility (CPD), plasma urea, NH3-N concentration and in situ degradation of SBM nitrogen. al 2, four groups each of six Barbarine lambs (initial LW 35.3 ± 3.7 kg) received for 90 days: hay ad libitum and 200 g SBM (D1), D1 and 20 g polyethylene glycol (PEG, MW 4000) mixed with SBM (D2), D1 and 100 g acacia with the SBM fed 1 h later when acacia was completely consumed (sequential strategy) (D3) or D3 and 20 g PEG fed with the SBM (D4). hylene glycol was here used to deactivate tannins. Hay intake and DM, organic matter and neutral detergent fibre digestibility were similar among dietary treatment (P > 0.05). However, supplementing lambs with SBM and acacia without PEG (D3) resulted in a significant decrease (P < 0.001) of CPD (0.664 versus 0.597, respectively for D1 and D3). Lambs given D1, D2 and D4 had similar growth rates (38.8–48.3 g/day) (P > 0.05). However, those supplemented with acacia without PEG (D3) had highest (P < 0.001) daily gain (66.7 g/day). The results of this study support the hypothesis that acacia could be used advantageously to improve sheep performance provided that appropriate TT to protein ratio is respected and the sequential strategy is adopted.