Supplementation of Acacia cyanophylla Lindl. foliage-based diets with barley or shrubs from arid areas (Opuntia ficus-indica f. inermis and Atriplex nummularia L.) on growth and digestibility in lambs

Twenty-eight Barbarine yearling lambs (4 months of age, average live weight 22.0 +/- 2.3 kg) given freshly cut Acacia cyanophylla Lindl. (acacia) foliage ad libitum supplemented with either 0.3 kg barley (B), 4.5 ka freshly cut pads of Opuntia ficus-indica f. inermis (cactus) (C), 0.3 ka barley and 1.4 ka freshly cut Atriplex nummularia L. foliage (atriplex) (B + A) or 4.5 ka cactus and 1.4 kg atriplex (C + A) were used in an 80-day study comprising growth, digestibility and N balance trials. The sheep were blocked by weight and within each block randomly allocated to four treatments giving seven animals per treatment. Condensed tannins (CT) content was high in acacia. Great amount of total oxalates was found in cactus (131 g/kg dry matter (DM)). Sheep consumed significantly less acacia when supplemented with cactus either alone (C) or with atriplex (C + A) as compared with (B) and (B + A) diets (28.7, 26.3, 36.6 and 38.3 a DM/kg W-0.75, respectively). The amount of drinking water was reduced in sheep given cactus as compared with those receiving barley and was increased with atriplex supply. Supplementing sheep with cactus alone substantially reduced organic matter (OM), crude protein (CP) and cell wall digestibility of the diet as compared with barley diet (B). These negative effects were reduced when cactus was fed in combination with atriplex. Nitrogen retention (g per day) with C-diet was proportionately about 0.61 lower than with (C + A)-diet and 0.32 lower with (C + A)-diet than with (B + A)-diet. Replacing barley by cactus had no effect upon the urinary excretion of allantoin, and thus on estimated microbial N supply to the small intestine. Atriplex supplied either with barley or cactus improved the efficiency of microbial protein synthesis. Replacing barley with cactus significantly reduced daily gains. Sheep on (B + A)-diet gained more (54 a per day) than those on the other dietary treatments. It was concluded that acacia may be utilised in sheep feeding provided that an adequate supply of both energy and nitrogen is made. Highest positive responses were obtained when barley was used as supplement of acacia with or without atriplex. Cactus alone was not able to replace barley as supplement to acacia. It should be offered in combination with a nitrogen-rich supplement, such as atriplex, to ensure normal microflora activity in the rumen. A diet of acacia supplemented with cactus and atriplex could be a cost-effective solution to nourish sheep during dry seasons. (C) 2002 Elsevier Science B.V. All rights reserved.