Intake and digestion in sheep given fresh or air-dried Acacia cyanophylla Lindl foliage

The effect of air-drying of Acacia cyanophylla Lindl foliage (acacia) on digestion in sheep was studied in November and December 1993 at Inra-Tunisia. Two groups of animals each including two intact and two rumen-cannulated 'Queue Fine de l'Ouest' adult sheep were offered 600 g dry matter (DM) lucerne hay and fresh or air-dried acacia foliage ad libitum. Diets were offered daily in two equal meals (08.00 and 16.00 h). A digestibility trial involving all animals and a digestion trial involving only rumen-cannulated animals were conducted according to a 2 x 2 x 4 and a 2 x 2 x 2 crossover design, respectively. Each experimental period lasted 25 days, with total faecal collections, rumen fluid samplings (0, 2, 4 and 8 h post feeding) and ruminal cellulolytic activity using the nylon bag technique being made over the final IO days. The organic matter, fibre (NDF, ADF and ADL) and crude protein (CP) contents were similar in fresh and air-dried acacia (42.9 vs 44.4, 27.0 vs 25.9, 14.1 vs 12.2, 11.9 vs 11.2% of DM, respectively). Acacia foliage, either fresh or air-dried, had a high content of insoluble nitrogen (79.0 and 84.5% of total nitrogen, respectively) and nitrogen bound to ADF (15.4 and 13.8% of total nitrogen, respectively). Air-drying reduced methanol extractable condensed tannins in acacia foliage (from 5.1 to 4.3 g catechin equivalent/100 g DM). DM intake of acacia was significantly increased (P < 0.05) by air-drying (from 52 to 56 g DM kg(-1) LW0.75). Remarkably, acacia intake was changed from day to day. Peaks were observed every 4 or 5 days in all animals. Sheep seem to regulate acacia consumption in function of tannin accumulation elsewhere in the body. The diet and acacia nutrient digestibilities were not affected by air-drying. CP digestibility of acacia was in the range 23-30%. Patterns of rumen fermentation assessed by pH, ammonia nitrogen and volatile fatty acid concentration and composition were similar in fresh and air-dried acacia treatments. There was no indication of any inhibition of ruminal fermentation with either diet. Cellulolytic activity was not affected by acacia air-drying. The increased intake of acacia foliage which occurred without any changes of acacia nutrient digestibilities and pattern of rumen fermentation suggests that the response was mediated probably by a decrease of the astringent taste of fresh acacia due to air-drying.