Abstract #M284

# M284
Effect of contrasting predicted residual feed intake on performance and CH4 emission of dairy cows fed 2 levels of forage neutral detergent fiber.
M. Aguerre*1, F. Sun2, J. M. Powell3, K. Weigel2, A. Pelletier4, P. Crump5, M. Wattiaux2, 1Animal and Veterinary Science Department, Clemson University, Clemson, SC, 2Dairy Science Department, University of Wisconsin-Madison, Madison, WI, 3U.S. Dairy Forage Research Center, Madison, WI, 4Soils Science Department, University of Wisconsin-Madison, Madison, WI, 5Department of Computing and Biometry, University of Wisconsin-Madison, Madison, WI.

The objective of this study was to determine the effects of selecting cows with contrasting predicted residual feed intake (RFI) on animal performance and CH4 emission and whether cow responses were affected by dietary forage neutral detergent fiber (NDF) level. Mid-lactation multiparous Holstein cows (n = 24) with contrasting predicted RFI were selected from a cohort of 47 cows using genotypic and phenotypic data from previous studies and grouped as low RFI (mean ± SD; −0.42 ± 0.13 kg/d) and high RFI (0.34 ± 0.11 kg/d), respectively. Half of the cows in each RFI group were randomly assign to a dietary treatment with either 22% or 30% forage NDF in a randomized complete block design. Following a 2-wk covariate period, cows were fed their assigned treatment diets for 4 weeks. Gas emission measurements were conducted in 4 tie-stall emission chambers during 3 consecutive days the last week of the covariate and experimental periods. Results are covariate-adjusted least squares means (±SEM). There was no RFI by forage NDF level interaction (P ≥ 0.05) for any of the measured variables. A tendency (0.05 < P < 0.10) was observed for higher MUN and CH4/DMI for high RFI-high forage NDF. Except for fat yield (1.74 vs. 1.50 ± 0.06 kg/d for low and high RFI, respectively), predicted RFI did not affect any measured responses. Increasing forage NDF reduced (P < 0.05) milk yield (44.3 vs. 40.6 ± 0.74 kg/d), fat-and-protein corrected milk (FPCM; 43.5 vs. 38.0 ± 1.24 kg/d), fat (1.77 vs. 1.51 ± 0.06 kg/d) and milk true protein yield (1.28 vs. 1.10 ± 0.04 kg/d). Greater forage NDF tended (P = 0.08) to decrease FPCM/DMI (1.56 vs. 1.43 ± 0.05), but increased MUN (11.2 vs. 12.7 ± 0.54 mg/dl) and CH4 emission (533 vs. 564 ± 19.7 g/d). Forage NDF level did not affect DMI (27.0 ± 0.74 kg/d), milk/DMI (1.58 ± 0.36), CH4/DMI (23.5 ± 0.77 g/kg), CH4/milk (15.4 ± 0.75 g/kg), and CH4/FPCM (14.9 ± 0.72 g/kg). Under the conditions of this study, selecting cow with lower RFI (presumably higher efficiency) had negligible effects on animal performance and CH4 emission. Increasing forage NDF level has negative impacts on animal performance and CH4 emission.

Key Words: greenhouse, forage, residual feed intake