Effect of Acacia cyanophylla Lindl. foliage supply on intake and digestion by sheep fed lucerne hay-based diets

Abstract

The effect of air-dried Acacia cyanophylla Lindl. foliage supply on rumen fermentation and nutrient digestion was studied in sheep fed on lucerne hay-based diets at INRA-Tunisia from February to June 1993. Five Queue Fine de l'Ouest sheep fitted with rumen cannulae received 700 g per day lucerne hay alone (0 g acacia) or supplemented with graded amounts of air-dried acacia (75, 150, 300 g and ad libitum) according to a 5 × 5 Latin square design. Each experimental period lasted 25 days of which 15 days were for diet adaptation and the following 10 days for measurements. Apparent digestibility of dietary organic matter (OM), crude protein (CP), neutral detergent fibre (NDF) and acid detergent fibre (ADF) was measured by total faeces collection. Fermentation parameters (pH, volatile fatty acids (VFA) content and composition, NH 3-N and protozoa in rumen liquor) were measured four times a day (0, 2, 4, and 8 h after the morning feeding). Rumen degradation characteristics of oat hay dry matter and soybean meal nitrogen were measured using the nylon bag technique. Acacia foliage had a high content of condensed tannins (45 g catechin equivalent per kg DM) and acid detergent lignin (161 g kg −1 of DM), as compared to lucerne hay (1 and 63 g kg −1 of DM, respectively). Crude protein content of acacia and lucerne hay was 136 and 166 g kg −1 of DM, respectively. About 20% of acacia total nitrogen was bound to fibre (ADF-N). Sheep fed acacia supplement ad libitum consumed up to 600 g DM per day of it. Total OM, CP, NDF and ADF digestibility were reduced by the two highest intake levels of acacia (300 g and ad libitum). Acacia supply caused a linear decrease of protozoa number in the rumen fluid. Ammonia nitrogen was significantly reduced with the two highest levels of acacia. There was a clear-cut negative effect of acacia supply on in-situ DM degradation and a tendency towards a decrease of the in-situ nitrogen degradation. The increase of VFA contents in sheep supplied with acacia may be the consequence of the increase of total intake. It is concluded that acacia supply had a negative effect on digestion of lucerne hay based diets when more than 150 g DM of acacia were included in the diet.