Thirty young male sheep were given air-dried foliage of Acacia cyanophylla Lindl. ad libitum and 400 g oat hay. Animals were divided into five equal groups each of which was supplemented with either 300 g concentrate with (CPEG) or without (C) 20 g polyethylene glycol 4000 (PEG) or urea-containing feedblocks with (BUPEG) or without (BU) PEG. One other treatment was PEG-containing feedblock without urea (BPEG). PEG was used to preferentially bind A. cyanophylla condensed tannins (CT). Feedblocks (BU, BPEG and BUPEG respectively) were made from olive cake (395, 376 and 353), wheat bran (263, 250 and 235), wheatfeeds (132, 125 and 118), quicklime (88, 83 and 78), salt (44, 42 and 39), mineral and vitamin supplement (12, 10 and 10), urea (66, 0 and 59) and PEG (0, 114 and 107 g/kg). These diets were used in growth (60 days) and metabolism (7 days) studies. Urea-containing feedblocks, as compared with concentrate, were higher in crude protein (CP; 235 v. 116 g/kg DM) and lower in metabolizable energy (6 v. 10 MJ/kg DM). The type of supplement (i.e. concentrate v. feedblocks) had no effect (P > 0·05) on A. cyanophylla DM intake, CP and neutral-detergent fibre (NDF) digestibilities and nitrogen (N) retention. However, concentrate-containing diets exhibited higher DM and organic matter (OM) digestibilities (P < 0·05), urinary excretion of allantoin (P < 0·05), microbial N supply (P < 0·001) and average daily gain (P < 0·001). PEG supply increased DM intake of A. cyanophylla, CP digestibility, N retention, allantoin voided in urine, microbial N supply and lamb growth. PEG-containing feedblocks enriched (BUPEG) or not (BPEG) with urea had similar effect on A. cyanophylla intake, DM, OM and NDF digestibilities, allantoin in urine, microbial N supply and average daily gain. These findings suggested that urea inclusion in feedblocks are not necessary and thus the feeding cost may be reduced. The higher amount of microbial N and daily gain in lambs given concentrate as compared with those on feedblock-supplemented diets was ascribed to the level of energy which was low in the latter diets. Enrichment of feedblocks with energy-rich ingredients such as molasses or cactus fruits could be a solution. This work confirmed that tannins depressed the nutritive value of this shrub species and lamb growth. However, the reduction was not drastic in the absence of PEG in the diet. Feedblock diet (BU) matched maintenance requirements of lambs while lambs on concentrate-supplemented diet (C) grew at a rate of 78 g/day. The choice between these two supplements will depend upon farm conditions and objectives.

Twenty-five male Barbarine lambs aged approximately 150 days were divided into five groups. All the animals received 400 g/day of oat hay and Acacia cyanophylla Lindl. foliage ad libitum. Two groups also received 300 g/ day of a mixture (70: 30) of processed barley and wheat bran, with or without 20 g polyethylene glycol 4000 (PEG), groups CPEG and C respectively. The three other groups had free access to feedblocks based on olive cake, and containing urea, urea and PEG, or PEG, groups BU, BUPEG and BPEG respectively. Lambs were slaughtered at age 230 days and meat quality was determined in the longissimus thoracis et lumborum muscle. Lean colour was significantly affected by dietary condensed tannins. Lightness (L*) was higher in those animals that did not receive PEG (P < 0·001) indicating that condensed tannins can cause lighter meat colour. This difference was not due to the ultimate pH, which was not affected by the inclusion of PEG in the diet. Meat from groups that received supplementation of concentrate had lower values of resistance to the Warner-Bratzler shear device compared with those that received feedblocks. This result was confirmed by a taste panel, that found samples from groups C and CPEG more tender than samples from groups BU, BUPEG and BPEG. Inclusion of PEG in the diet increased intensity of flavour (P < 0·05) but had no effect on overall acceptability. Meat from animals that had received the concentrate had higher overall acceptability (P < 0·05) than meat from animals that received the feedblocks. No differences were found in meat chemical composition.

Polyethylene glycol-4000 (PEG) was used to inactivate tannins in Acacia cyanophylla Lindl foliage. In the first of two experiments, four groups of five Barbarine sheep were held in metabolism crates so that intakes, apparent digestibilities, nitrogen balances and urinary excretion of allantoin could be measured. The second experiment involved four groups of three male Queue Fine de l'Ouest sheep fitted with rumen cannulae and housed in individual pens to measure rumen fermentation parameters and dry matter in situ degradation of A. cyanophylla foliage. All animals received fresh A. cyanophylla foliage ad libitum and 330 g concentrate on a daily basis. In each experiment, three groups of sheep received 20 g PEG daily, either mixed with concentrate (PEG-concentrate), dissolved in drinking water (PEG-water) or sprayed as a solution on A. cyanophylla foliage at the point of feeding (PEG-treatment). The fourth group was not supplied with PEG (control). Dry-matter intake of A. cyanophylla was low (28·3 g/kg metabolic live weight (M0·75) per day) and increased in sheep given the PEG-concentrate diet (38·2 g/kg M0·75 per day). PEG-concentrate and PEG-water diets resulted in an improvement in protein utilization as indicated by an increase of crude protein apparent digestibility (2·1 and 1·9 fold, respectively), nitrogen retention (3·2 fold with both dietary treatments) and urinary excretion of allantoin (1·9 and 1·5 fold, respectively). Improvements obtained with PEG-treatment diet were low and in general not significant (P > 0·05). Low neutral-detergent fibre and acid-detergent fibre apparent digestibility coefficients of diets led to the conclusion that conventional detergent extraction techniques are questionable in determining the in vivo digestibility of cell wall constituents for tannin-rich forages. Results from rumen fluid analyses indicated that sheep given PEG-containing diets had higher ammonia-nitrogen and volatile fatty acid (VFA) concentrations (P < 0·05). These results, coupled with the increase of allantoin excretion gave clear evidence that the efficiency of microbial synthesis was improved with PEG addition. The absence of change in ruminal pH and molar proportions of individual VF A suggested similar fermentation patterns among all dietary treatments. PEG supply increased the slowly degradable fraction of A. cyanophylla foliage incubated in the rumen (P < 0·05), thus dry matter potential degradability (a + b) was highest in sheep given PEG-containing diets. It is concluded that the affinity of acacia tannins to PEG, increased the availability of degradable proteins, which resulted in an improvement of the nutritive value of acacia foliage. However, for practical situations, adding PEG to concentrate or to drinking water is recommended for sheep browsing A. cyanophylla trees in the field or fed indoors.