Effects of multinutrient blocks and polyethylene glycol 4000 supplies on intake and digestion by sheep fed Acacia cyanophylla Lindl. foliage-based diets

The effect of multinutrient block supply and polyethylene glycol 4000 (PEG) on intake, digestion and rumen fermentation was studied in sheep fed with air-dried Acacia cyanophylla foliage (acacia)-based diet. In Experiment I, six Noire de Thibar breed sheep (BW = 46 kg) were used in double 3 x 3 Lati n square design. All diets included about 360 g of dry matter (DM) of oat-v etch hay and acacia ad libitum. Diet DO was without a block supplement. Die t D1 included a urea-molasses-mineral block (B1). While D2 included another type of block (B2) that differed from B1 essentially by adding polyethylen e glycol 4000. Each experimental period lasted 33 days (21 days for adaptat ion and two periods of 5 days for measurement separated by 2 days for rest) . Feed intake, apparent digestibility of organic matter (OM), crude protein (CP) and crude fibre (CF) and retained nitrogen (N-r) were measured by tot al faecal collection. In Experiment II, four Noire de Thibar sheep (BW = 53 kg) fitted with rumen cannulae were fed sequentially DO, D1 and D2, respec tively, to 90% of intake levels as measured in Experiment I on metabolic we ight (MW) base. Fermentation parameters in lumen liquid (pH, NH3-N, volatil e fatty acid (VFA)) were measured at 0, 2, 5, 8, 10, 13, 16 and 21 h after the morning meal. Protozoal number and composition in rumen fluid were dete rmined at 2 h sampling time. Solid digesta kinetics through the rumen was m easured using chromium (Cr) mordanced acacia. The DM and CP degradation of acacia was determined using the nylon bag technique. Acacia had a relatively high content of condensed tannins (41 g kg(-1) of D M) and acid detergent lignin (176 g kg(-1) of DM). BI and B2 were high in C F (381 and 369 g kg(-1) of DM, respectively) compared to acacia (127 g kg(- 1) of DM, 20% bound to fibre) and hay (75 g kg(-1) of DM). The two kinds of blocks improved similarly (P < 0.001) acacia DM intake by 195 g. Block 1 i ncreased (P < 0.001) only diet CP digestibility and Nr. Block 2 increased ( P < 0.05) by a low extent DM and OM digestibility compared to D1, and remar kably (P < 0.001) CP digestibility and Nr compared to DO and D1. Block supp lies considerably increased water intake. Both B1 and B2 increased (P < 0.001) NH3-N and VFA concentrations in the ru men liquid with a positive specific effect of B2 (PEG). VFA molar proportio n was significantly modified by B1 and B2. B1 and B2 decreased acetate prop ortion and increased propionate and butyrate proportions as compared to DO (P < 0.001). Protozoal number in rumen fluid was increased significantly by B1 and B2 (P < 0.001). PEG-containing block (B2) increased protozoal numbe r as compared to B1. Both B1 and B2 increased (P < 0.001) solid outflow rat e, with a specific increasing effect of B2, (D2) when compared to B1 (D1). Blocks supply did not modify in situ DM degradability of acacia, but B2 imp roved (P < 0.05) effective degradability of CP when compared to DO and D1 w hich were similar. It is concluded that both B1 and B2 improved the nutriti ve value of acacia-based diet. A further positive effect was noted in D2 (P EG), especially for N metabolism. (C) 2000 Elsevier Science B.V. All rights reserved.