MICROBIOLOGICAL EVALUATION OF ACACIA-ANGUSTISSIMA AS A PROTEIN-SUPPLEMENT FOR SHEEP

The effect of Acacia angustissima on rumen fermentation was evaluated. Acacia angustissima was fed to two groups of cannulated Ethiopian hig hland sheep. One group (three animals) was directly supplemented with 300 g per head day(-1) of sun-dried A. angustissima. These animals die d after 9 and 21 days and consumed only 75-100 g day(-1) of the supple ment at any time. The second group (three animals) was gradually adapt ed by offering incremental levels of 50, 75, 100, 150 and 200 g per he ad day(-1) of A. angustissima for 21 days per level. The gradually ada pted animals did not develop toxicity symptoms suggesting adaptation o f microflora in the rumen or ability to modify the toxic principle in the plant. Transfer of rumen contents from the adapted animals to othe r unadapted sheep provided protection from A. angustissima toxicity wh en the animals were suddenly challenged with 200 g per head day(-1) of A. angustissima after the transfer. Numbers of ciliate protozoa and f ungal sporangia were estimated. The protozoal numbers fluctuated with the level of the supplement and numbers decreased in sheep consuming 1 00, 150 and 200 g of the supplement. The fungal sporangia numbers were inversely related to protozoal numbers. Effect on in sacco fibre (nat ive hay) degradation was also investigated. There was no significant d ifference (P > 0.05) in fibre degradation in sheep supplemented with A . angustissima compared with those fed maize stover alone. The effect of level of supplement was, however, significant (P < 0.01). In vitro effect of A. angustissima on mixed ruminal bacteria was investigated u sing gas and volatile fatty acid (VFA) production as indices of fermen tation. Gas and VFA production from A. angustissima were significantly (P < 0.01) lower than those from Sesbania sesban (used as control) at 12 h. Acetone (70%) extracts of A. angustissima inhibited the growth of Ruminococcus albus 8, Ruminococcus flavefaciens FD-1, Prevotella ru minicola D31D and Streptococcus bovis JB1 while Selenomonas ruminantiu m D was not affected at the levels used. Bacterial colonies resistant to toxicity of A. angustissima were isolated. (C) 1997 Elsevier Scienc e B.V.