Different means of administering polyethylene glycol to sheep: effect on the nutritive value of Acacia cyanophylla Lindl. foliage

Polyethylene glycol-4000 (PEG) teas used to inactivate tannins in Acacia cy anophylla Lindl. foliage. In the first Of two experiments, four groups of f ive Barbarine sheep were held in metabolism crates so that intakes, apparen t digestibilities, nitrogen balances and urinary excretion of allantoin cou ld be measured. The second experiment involved four groups of three male Qu eue Fine de l'Ouest sheep fitted with rumen cannulae and housed in individu al pens to measure rumen fermentation parameters and dry matter in situ deg radation of A. cyanophylla foliage. All animals received fresh A. cyanophyl la foliage ad libitum and 330 g concentrate on a daily basis. In each exper iment, three groups of sheep received 20 g PEG daily, either mixed with con centrate (PEG-concentrate), dissolved in drinking water (PEG-water) or spra yed as a solution on A. cyanophylla foliage at the point of feeding (PEG-tr eatment). The fourth group was not supplied with PEG (control). Dry-matter intake of A. cyanophylla was low (28.3 g/kg metabolic live rc,eight (M-0.75 ) per day) and increased in sheep given the PEG-concentrate diet (38.2 g/kg M-0.75 per day). PEG-concentrate and PEG-water diets resulted ill an impro vement 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-deter gent fibre and acid-detergent fibre apparent digestibility coefficients of diets led to the conclusion that conventional detergent extraction techniqu es are questionable in determining the in vivo digestibility of cell wall c onstituents for tannin-rich forages. Results from rumen fluid analyses indi cated that sheep given PEG-containing diets had higher ammonia-nitrogen and volatile fatty acid (VFA) concentrations (P < 0.05). These results, couple d with the increase of allantoin excretion gave clear evidence that the eff iciency of microbial synthesis teas improved with PEG addition. The absence of change in ruminal pH and molar proportions of individual VFA suggested similar fermentation patterns among all dietary treatments. PEG supply incr eased 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 affin ity of acacia tannins to PEG, increased the availability of degradable prot eins, which resulted in an improvement of the nutritive value of acacia fol iage. However, for practical situations, adding PEG to concentrate or to dr inking water is recommended for sheep browsing A. cyanophylla frees in the field or fed indoors.