Effects of "Pais" grape marc on in vitro methane production and ruminal fermentation parameters of a forage diet

Abstract Grape marc (GM) is a viticulture by-product used as cattle supplement in periods of shortage of conventional feed sources. It contains fats, high concentrations of polyphenols and has been reported to reduce enteric methane (CH4) emissions. In-vitro batch culture was used to study the effects of substitution of mixed hay (MH) for a traditional Chilean variety (Vitis vinifera “País”) of GM on in vitro dry matter disappearance (IVDMD), rumen fermentation parameters (short chain fatty acids, pH, partitioning factor), gas and CH4 production in a 60% forage diet (dry matter, DM). The study was a randomized complete design with 3 treatments and 3 replicates, incubated for 24 h at 39º C. Treatments were: T1 (Control): 20% MH, 40% corn silage, 40% concentrate; T2 = 10% MH, 10% GM, 40% corn silage, 40% concentrate; T3 = 20% GM, 40% corn silage, 40% concentrate. Means were compared with the Tukey test (P < 0.05), and polynomial contrasts. Substitution of MH with GM significantly reduced ammonia nitrogen (NH3-N) by 50% (P < 0.05), although it did not affect IVDMD, gas production or other rumen fermentation parameters (P > 0.05). Total CH4 (mg) linearly decreased (P = 0.013) as concentrations of GM increased. Methane production (mg/g DM incubated) and yield (mg/g DM digested) decreased linearly (P = 0.002 and P = 0.003, respectively) as inclusion of GM increased. Inclusion of GM at 20% reduced CH4 production by 19% and CH4 yield by 16.4%. These results indicate that partial substitution of dietary fiber sources with traditional Chilean País GM in high fiber diets is a viable feeding alternative, and can decrease environmental impact (lower CH4 and ammonia emissions) of ruminant livestock, without negatively affecting rumen fermentation parameters.