Increasing the nutritive value of a rice straw-based diet using mulberry and Leucaena to promote the growth performance of lambs

The objective of this study was to evaluate the effect of substituting urea and rice bran with mulberry or a mixture of mulberry and Leucaena in the diet on growth rate, feed intake, nutrient digestibility, nitrogen balance, rumen fermentation, estimated methane production, and rumen microbial protein synthesis in lambs fed a basal diet of urea-treated rice straw. The experiment consisting of three supplement treatments with six replications was arranged in a randomized block design. Eighteen lambs with an initial body weight of 14.4 ± 3.35 kg were used. The three supplement treatments were (i) urea–rice bran (UR) comprising 38.5% of the diet, (ii) mulberry foliage comprising 30% of the diet as UR substitution (Mb), and (iii) a mixture of mulberry–Leucaena foliage in a 1:1 ratio comprising 30% of the diet as UR substitution (MbL). All lambs were fed a basal diet of urea-treated rice straw, and the diets were formulated with iso-energy and iso-protein content. Substituting urea rice bran with either mulberry foliage or a mixture of mulberry–Leucaena foliage yielded similar effects on urinary and faecal nitrogen excretions, nitrogen retention, rumen fermentation, microbial nitrogen yield, and the average daily gain of lambs (71.4 g/day). Both the mulberry and the mulberry–Leucaena mixture supplements exhibited higher dry matter intake by 15.4% and 9.9% and neutral detergent fibre digestibility by 17.5% and 14.5%, respectively, compared to urea–rice bran supplementation. These findings indicate that mulberry or a mixture of mulberry–Leucaena foliage is a promising alternative to replace urea–rice bran in improving the nutritional values of the rice straw basal diet for sheep.