Intake, milk production, and methane emission of dairy cows fed diets that differ in ruminal in vitro NDF digestibility

The objective of this study was to determine how feeding diets that differed in dietary ruminal in vitro NDF digestibility (IVNDFD) affected DMI, milk production, and CH4 emission from lactating dairy cows. Twenty four multiparous Holstein cows (mean ± SD; 717 ± 67 kg of BW; 160 ± 49 d in milk) were randomly assigned to four dietary treatments in a randomized complete block design study. Four levels of dietary IVNDFD (digestibility determine after 30 h of incubation) were achieved by substituting corn stover (15% of dietary DM) with alkaline-treated corn stover (at 7.0% Ca(OH)2 of stover DM; stover DM was 50%) in stepwise increments (0, 5, 10, and 15% of dietary DM). Following a 2-wk covariate adjustment period, cows were assigned to dietary treatments for 6 wk. Cows were fed a total mixed ration with (DM basis) 55% forage, 45% concentrate, 16.6% crude protein, 28.7% NDF, and 23.7% starch once daily. Replacing untreated corn stover with 5, 10, and 15% treated corn stover increased dietary IVNDFD by 2.2, 4.3, and 6.2% units, respectively. Performance and CH4 emission measurements were conducted in four tie-stall emission chambers during three consecutive days the last week of the covariate and experimental periods. Treatment effects are presented as covariate-adjusted least squares means (± SEM). Increasing IVNDFD in the diet had no effect on DMI (21.3 ± 1.3 kg/d), milk yield (32.1 ± 2.2 kg/d), fat-and-protein corrected milk yield (FPCM; 29.9 ± 2.3 kg/d), FPCM/DMI (1.42 ± 0.1), CH4 emission (524 ± 35 kg/d), and CH4/FPCM (18.4 g/kg ± 1.7). However, with increasing levels of IVNDFD in the diet there was a linear decrease (P = 0.02) in CH4/DMI from 26.4 to 23.3 (g/kg) and a tendency (P = 0.06) to reduce CH4/milk from 18.8 to 14.4 (g/kg). Also, a tendency (P = 0.08) for a quadratic response was observed for CH4/milk; increasing dietary IVNDFD by 2.2 and 6.2% units decreased CH4/milk to 17.7 and 14.4 g/kg respectively, compared with 15% untreated corn stover diet (18.8 g/kg), but a 4.4% increase on IVNDFD resulted in the highest yield of CH4/milk (20.0 g/kg). Under the conditions of this study increasing IVNDFD in the diet by as much as 6.2% units had little impact on performance or emission of CH4 (g/d), but decrease CH4 emission per unit of DMI by 12% and decreased CH4 emission per unit milk by 23%.