Evaluation of rumen fermentation kinetics of some by-products using in situ and in vitro gas production technique

Abstract

This study was carried out to determine the chemical composition and estimation of nutritive value of brewers’ grain, apple pomace, orange pulp and lemon pulp by-product using in vitro gas production technique. Test feeds had significant differences in chemical composition. Brewers’ grain had the highest (P<0.05) crud protein (19.5 % DM) and ether extract (7.8 % DM). Apple pomace contained the highest neutral detergent fibre (43.3 % DM), acid detergent fibre (32.3 % DM) and lowest ash (3 % DM). Cumulative gas production was recorded at 2, 4, 6, 8, 12, 16, 24, 36, 48 and 72 h of incubation and the equation Y = A (1-e-ct) was used to describe the kinetics of gas production. Potential gas production (A) and rates of gas production (c) differed (P<0.05) among feeds. Apple pomace showed higher potential gas production (A) (341 ml g-1 DM) and orange pulp had higher rate of gas production (c) (0.09 h-1) than the other feeds. Inversely, lemon pulp (220 ml g-1 DM) had lower potential gas production than the other test feeds. The metabolizable energy (ME) (MJ kg-1 DM) content of feeds was calculated using gas production data. According to gas production data, the ME values ranged from 7.66 in lemon pulp to 10.83 MJ kg-1 DM in apple pomace. For in situ technique duplicate dacron bags were incubated for 0, 2, 4, 8, 12, 24, 48 and 72 h in two wethers fitted with ruminal cannulas. The model y = a+b (1-e-ct) was used for determination of degradation characteristics. Orange pulp had higher soluble DM (a) (36.9 %), lemon pulp had higher insoluble potentially degradable DM (b) (62 %) and orange pulp had higher degradation rate (0.112 % h-1) than other feeds. It was concluded that regarding different chemical composition of test feeds, the in situ dry matter degradability, in vitro gas production and ME, SCFA and OMD of feeds showed different values.