Multiple-factor associative effects of peanut shell combined with alfalfa and concentrate determined by in vitro gas production method

The associative effects (AE) between concentrate (C), peanut shell (P) and alfalfa (A) were investigated by means of an automated gas production (GP) system. The C, P and A were incubated alone or as 40 : 60 : 0, 40 : 45 : 15, 40 : 30 : 30, 40 : 15 : 45, 40 : 0 : 60 and 30 : 70 : 0, 30 : 55 : 15, 30 : 40 : 30, 30 : 25 : 45, 30 : 10 : 60, 30 : 0 : 70 mixtures where the C : roughage (R) ratios were 40 : 60 and 30 : 70. Samples (0.2000 ± 0.0010 g) of single feeds or mixtures were incubated for 96 h in individual bottles (100 ml) with 30 ml of buffered rumen fluid. GP parameters were analysed using a single exponential equation. After incubation, the residues were used to determine pH, dry matter digestibility (DMD), organic matter digestibility (OMD), volatile fatty acids (VFA) and ammonia nitrogen (NH3-N) of the incubation fluid, and their single factor AE indices (SFAEI) and multiple-factors AE indices (MFAEI) were determined. The results showed that group of 30 peanut shell had higher SFAEI of GP48 h, DMD, OMD and total volatile fatty acids (p < 0.05) and MFAEI (p < 0.05) than groups 60, 45 and 0 when C : R was 40 : 60. The group of 10 peanut shell showed higher SFAEI of GP48 h, DMD and OMD (p < 0.05) than groups 70, 55 and 40 and MFAEI (p < 0.01) when C : R was 30 : 70. It is concluded that optimal SFAEI and MFAEI were obtained when the C : P : A ratios were 40 : 30 : 30 and 30 : 10 : 60.