Effects of mulberry leaves to replace rapeseed meal on performance of sheep feeding on ammoniated rice straw diet

This study was conducted to investigate effects of leaves of mulberry tree (Morus alba) as a protein supplement to isonitrogenously replace rapeseed meal (RSM) on performance of growing lambs offered ammoniated rice straw (ABRS) (Trial 1), and to evaluate the digestive characteristics of the ABRS supplemented with different ratios of RSM and mulberry leaves in terms of in vitro gas production (Trial 2). In Trial 1, 45 Huzhou lambs were divided into five equal groups according to their body weight and gender. Lambs in each group were kept in three pens (male, female and mixed (one male and two females)), and received one of the following dietary treatments: 100 g RSM (A), 75 g RSM plus 60 g mulberry leaves (B), 50 g RSM plus 120 g mulberry leaves (C), 25 g RSM plus 180 g mulberry leaves (D), and 240 g mulberry leaves (E). All animals were given ABRS ad libitum along with 100 g ground corn per head per day. The intake of ABRS was slightly increased with the supplementary level of mulberry leaves, and hence total intake increased with the increasing level of mulberry leaves. The growth rates were higher in diets A and E than those in other treatments (P<0.05), with little difference between diets A and E, and the slowest in C. Animals of all genders showed a similar trend, though male lambs was higher in weight gain than the female. While feed efficiency was higher in diet A, concentrate consumption per kilogram of weight gain was lower when higher level of mulberry leaves was supplemented (diets D and E). Feed cost per kilogram gain was lower in diets E and A compared to other treatments. Degradation of dry matter in the rumen of sheep were higher for mulberry leaves than for RSM, but crude protein was less degraded for mulberry leaves than for RSM. The potential GP was significantly higher in diet A than those in B, C and D (P<0.05), and higher in E than in C (P<0.05) (Trial 2), indicating a negative associate effect of mulberry leaves and RSM on digestion. It is inferred that mulberry leaves may be used as a protein supplement to ammoniated straw diets to fully substitute for RSM, but these two supplements should unlikely be supplemented together to avoid the negative associate effect.