Livestock Research for Rural Development 14 (6) 2002

A digestibility trial was conducted to evaluate the nutritive value of diets composed of either Cambodian full-fat rubber (Hevea brasiliensis) seeds or soya beans using 16 Mong Cai*Large White pigs. Rubber seeds of unknown falling day and storing period, and extruded soy beans were used in this study. Water spinach (Ipomoea aquatica) was given ad libitum as a complementary protein-rich foliage supplement. The design was a 2*2*2 factorial arrangement to compare the effect of protein source (full-fat rubber seeds or soya beans), DL-methionine supplementation (0 or 0.3%) and animal live weight (40 or 60 kg). Average crude protein content of the diets was 13.1 ± 1.05% in dry basis and voluntary intake of water spinach was 22.3 ± 2.6 and 16.2 ± 1.4% of the consumed dry matter, for animals of 40 and 60 kg live weight, respectively. There was no significant interaction (P>0.05) amongst any of the studied factors. There was no significant influence of animal live weight on digestibility coefficients. Full-fat rubber seeds were associated with a highly significant decrease in DM and organic matter digestibility, compared with soya beans, but there was no effect on N digestibility, which was always low. Digestibility indices appeared to be higher in diets supplemented with DL-methionine, and this effect tended to be significant for organic matter digestibility. The high crude fibre content in the diets had a highly significant, negative influence on digestibility of DM and organic matter (R 0.73 and 0.75, respectively). There was no influence of dietary crude fibre level on N digestibility. A slight decrease in dry matter digestibility in the rubber seed diet does not necessarily imply a decrease in energy availability to the animals due to the high crude fat content of this diet (on average 12.5 ± 0.74 % in dry basis). It could be suggested that little, if any, N is linked to the cell walls in the rubber seed since in this experiment full-fat rubber seeds accounted for approximately 34 % of the diets.