Effects of diet forage source and neutral detergent fiber content on milk production of dairy cattle and methane emissions determined using GreenFeed and respiration chamber techniques

Strategies to mitigate greenhouse gas emissions from dairy cattle are unlikely to be adopted if production or profitability is reduced. The primary objective of this study was to examine the effects of high maize silage (MS) vs. high grass silage (GS) diets, without or with added neutral-detergent fiber (NDF) on milk production and methane emission of dairy cattle, using GreenFeed (GF) or respiration chamber (RC) techniques for methane emission measurements. Experiment 1 was 12-wks in duration with a randomized block continuous design and 40 Holstein cows (74 d in milk; DIM) in free-stall housing, assigned to 1 of 4 dietary treatments (n = 10 per treatment), according to calving date, parity and milk yield. Milk production and dry matter intake (DMI) were measured daily, and milk composition measured weekly, with methane yield (g/kg DMI) estimated using a GF unit (wks 10 to 12). Experiment 2 was a 4 × 4 Latin Square Design with 5-wk periods and 4 dairy cows (114 DIM) fed the same 4 dietary treatments as in experiment 1. Measurements of DMI, milk production and composition occurred in wk 4, and DMI, milk production and methane yield were measured for 2 d in RC during wk 5. Dietary treatments for both experiments were fed as TMRs offered ad libitum and containing 500 g silage/kg DM comprised of either 75:25 MS:GS (MS) or 25:75 MS:GS (GS), without or with added NDF from chopped straw and soy hulls (+47 g NDF/kg DM; MSNDF and GSNDF). In both experiments, compared to high GS, cows fed high MS had a higher (P = 0.01) DMI, greater (P = 0.01) milk production, and lower (P = 0.02) methane yield (24% lower in experiment 1 using GF and 8% lower in experiment 2 using RC). Added NDF increased (or tended to increase) methane yield for high MS, but not high GS diets (P = 0.02 for experiment 1 and P = 0.10 for experiment 2, forage type × NDF interaction). In the separate experiments the GF and RC methods detected similar dietary treatment effects on methane emission (expressed as g/d and g/kg DMI), although the magnitude of the difference varied between experiments for dietary treatments Overall methane emission and yield were 448 g/d and 20.9 g/kg DMI using GF for experiment 1 using GF and 458 g/d and 23.8 g/kg DMI for experiment 2 using RC, respectively