In-vitro fermentation characteristics and methane reduction potential of mustard cake (Brassica juncea L.)

To assess the effect of mustard cake (Brassica juncea L.) levels in concentrate mixtures and in composite feed mixtures (CFMs) on in-vitro fermentation characteristics and methane production.

Five concentrate mixtures were prepared with containing 30% oil cake, where linseed cake was replaced by mustard cake at the rate of 0%, 7.5%, 15.0%, 22.5%, and 30% in concentrate mixture. Mustard cake contained glucosinolate 72.58 µmol/g oil free dry matter (DM) and contents in diet were 0, 5.4, 10.9, 16.3, and 21.8 µmol/g of concentrate mixture, respectively. Concentrate mixture containing 15.0% mustard cake was found to produced minimum methane which was then used for the preparation of CFM containing 0%, 25%, 50%, and 75% levels with gram straw.

Increased levels of mustard cake in concentrate mixtures had a linear decrease (p<0.05) in the total gas production, and the 15% inclusion showed lowest methane concentration (quadratic, p<0.01). The degradability of DM and organic matter (OM) of concentrate mixtures did not change, however, pH and NH₃-N concentrations of the fermentation medium showed linear (p<0.05) reductions with increased mustard cake levels. Increased levels of 15% mustard cake containing concentrate mixture in CFMs exhibited a trend (p=0.052) of increased gas production, whereas methane concentration in total gas, methane produced and degradability of DM and OM were also displayed a linear increase (p<0.05). However, the pH, NH₃-N, and total volatile fatty acid levels decreased linearly (p<0.05) with increased levels of concentrate in CFMs.

Reduction in methane production was evidenced with the inclusion of mustard cake in concentrate mixture at 15% level, and the CFMs with 25% concentrate, which contained 15% mustard cake, exhibited an improved fermentation and reduced methane production.