Effects of Forage Source and NDF Concentration on Methane Emissions and Milk Production of Dairy Cows

Abstract Text: Strategies to mitigate greenhouse gas emissions from dairy cows are unlikely to be adopted if production or profitability is reduced.  Dietary manipulation to reduce methane emissions can be readily used and may benefit productivity. The objectives of this study were to examine the effects of silage type and diet NDF concentration on methane emissions and milk production of dairy cows. A 12-week randomized block continuous design was used with 40 mid-lactation Holstein cows (74 DIM ± SEM 2.57) assigned to one of 4 treatments (10 cows each) according to calving date, parity and milk yield. Milk production and DMI were measured daily and milk composition measured weekly (weeks 3 to 12), and methane emissions estimated using a GreenFeed automated head chamber (weeks 10 to 12).  Four isonitrogenous diets were fed as total mixed rations (TMR) containing 50% silage (DM basis) offered ad libitum.  Silage was comprised of either 25:75 (MS) or 75:25 (GS) grass silage:maize silage on a DM basis, without or with additional NDF from chopped straw and soy hulls (+ 47 g NDF/kg TMR DM).  A commercial calf pellet was included in the TMR (weeks 1 to 8) or provided via the GreenFeed (weeks 9 to 12).  Data (weeks 10 to 12) were analyzed using mixed models for effects of silage, NDF, and their interaction. Cows fed MS had a greater milk yield (P < 0.01; 34.5 vs. 29.0 kg/d), milk protein yield (P < 0.001; 1076 vs. 926 g/d), DMI (P < 0.001; 24.6 vs. 19.3 kg/d), lower milk fat concentration (P < 0.001; 3.59 vs. 4.19 %) and lactose yield (P < 0.01; 1540 vs. 1286 g/d), and lower methane yield (P < 0.001; 17.7 vs. 24.1 g/kg DMI), compared to GS.  Added NDF increased methane production (410 vs. 461 g/d) and yield (16.5 vs. 18.9 g/kg DMI) when MS was fed, but not GS (460 g/d and 24.0 g/kg DMI, respectively), as indicated through a silage by NDF interaction (P < 0.10). Effects of silage type and NDF on methane emissions may be attributable to changes in rumen digesta dynamics, including rumen outflow and retention time, and warrants further investigation.

Keywords: Methane, dairy cows, forage NDF