Study on the associative effects of different proportions of soybean pod, alfalfa and concentrate on the diets at different ratio of concentrate to roughage in vitro

This study aimed to determine the associative effects (AEs) of 28 feed combinations of concentrate/soybean pod/alfalfa at different concentrate-roughage ratios that were incubated for 72 h in single tubes (120 ml) which were added 30 ml rumen buffered fluid. The gas production (GP) at 0, 2, 4, 6, 9, 12, 24, 36, 48, 72 h was recorded. A single exponential equation was applied to calculate the GP parameters a (rapid GP), b (slow GP), a + b (GP potential) and c (rate constant of slow GP that can reflect the specific process of GP, rapid and slow GP and GP rate). The AEs were calculated by 72 h GP and weighted estimation value of each combination. After 72 h incubation, pH, volatile fatty acids (VFA) and ammonia nitrogen (NH3-N), dry matter digestibility (DMD), organic matter digestibility (OMD) were determined the incubation fluid and residues. The single-factor AE index (SFAEI) and multiple-factor AE index (MFAEI) were computed. The results showed that the groups 50 : 50 : 0, 40 : 60 : 0, 60 : 20 : 20, 60 : 10 : 30, 50 : 30 : 20, 50 : 20 : 30, 40 : 50 : 10, 30 : 55 : 15, 30 : 40 : 30, 20 : 65 : 15, 20 : 50 : 30 had higher GP72 h, a, b, DMD, OMD, NH3-N, in addition, higher AE of GP, DMD, OMD, total VFA and NH3-N than those of the other groups (P < 0.05 or P < 0.01), especially the group 30 : 55 : 15 was optimal. In conclusion, in vitro data reveal reliable fermentability and the highest SFAEI and MFAEI occurred when concentrate, soybean pod and alfalfa were combined at the ratios of 50 : 50 : 0, 40 : 60 : 0, 60 : 20 : 20, 60 : 10 : 30, 50 : 30 : 20, 50 : 20 : 30, 40 : 50 : 10, 30 : 55 : 15, 30 : 40 : 30, 20 : 65 : 15, 20 : 50 : 30.