PSXIII-4 - Effects of “País” grape marc on in vitro methane production and ruminal fermentation parameters of a forage diet

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.