Effect of nitrate and fumarate in Prosopis cineraria and Ailanthus excelsa leaves-based diets on methane production and rumen fermentation

- Methane production decreased for leaves-based diets compared with grass diets.
- The extent of inhibition of methane varied depending upon diet type.
- Nitrate and fumarate suppressed methane production additively in leaves-based diets.
- Inhibition of methane was higher for low roughage diets than high roughage diets.
- Prosopis cineraria and Ailanthus excelsa leave diets improved rumen fermentation.

This study investigated the effect of nitrate and fumarate in Prosopis cineraria (khejri) and Ailanthus excelsa (ardu) leaves-based diets on methane production, feed degradability and rumen fermentation in vitro. The treatments were arranged in a 4 × 3 × 2 factorial design. The factors studied were four diets: cenchrus grass (Cenchrus ciliaris) hay (CC), cenchrus hay, ardu and khejri leaves (50:25:25; CAKC), cenchrus hay and ardu leaves (50:50; CAC), and cenchrus hay and khejri leaves (50:50; CKC) as roughage sources, each supplemented with a concentrate mixture; three additives: control (without any additives), nitrate (5 mM) and fumarate (10 mM); and two ratios of roughage to concentrate (R:C): 70:30 and 40:60. Methane production was lowered (P < 0.05) by the grass hay and leaves-based diets (CAKC, CAC and CKC) than CC (56, 48, 39 and 32 ml/g digested organic matter (DOM) for CC, CAKC, CAC and CKC, respectively for low R:C diet; 66, 64, 58 and 52 ml/g DOM for CC, CAKC, CAC and CKC, respectively for high R:C diet), but the extent of inhibition varied depending upon diet type. Addition of nitrate and fumarate suppressed methane production additively in leaves-based diets, and this response was markedly higher for low R:C diet than high R:C diet. In general, leaves-based diets had greater degradability than the CC, and the effect was more pronounced for high R:C (i.e. high leaves) diets compared with low R:C diets (65% and 59% for leaves-based diets and CC, respectively for high R:C diet; 74% and 68% for leaves-based diets and CC, respectively for low R:C diet). Nitrate decreased the degradability of organic matter (OM) compared with control for both low (5.6%) and high (6.1%) R:C diets. Fumarate lowered OM degradability by 5.7% for high R:C diets. Nitrate increased ammonia concentration compared with CC and fumarate. Ammonia concentration was higher for leaves-based diets than CC except for CKC plus nitrate. Nitrate (12.8% and 8.4% for high and low R:C diets, respectively) and fumarate (11.6% and 18.8% for high and low R:C diets, respectively) increased total volatile fatty acid concentrations and microbial biomass yields, which were greater for leaves-based diets than the CC. This study demonstrated that addition of fumarate and nitrate in diets containing P. cineraria and A. excelsa leaves may additively decrease methane production and improve rumen fermentation.