Impact of dietary forage proportion and crossbreeding on feed efficiency and methane emissions in lactating dairy cows

Increasing forage proportion (FP) in the diets of dairy cows would reduce competition for human edible foods and reduce feed costs, particularly in low-input systems. However, increasing FP reduces productivity and may increases methane (CH4) emissions parameters. This work aimed to investigate the impact of FP and breed on feed efficiency and CH4 emission parameters. Data from 32 individual experiments conducted at the Agri-food and Biosciences institute between 1992 and 2010 were utilised in this study resulting in data from 796 Holstein-Friesian (HF), 50 Norwegian Red (NR), 46 Jersey x HF (J×HF) and 16 NR × HF cows. Diets consisted of varying proportions of forage and concentrate dependent on the experimental protocols of each experiment. A linear mixed model was used to investigate the effect of low (LFP; 10% to 30%), medium (MFP; 30% to 59%), high (HFP; 60% to 87%) and pure (FOR; 100%) FP (DM basis) and breed on feed efficiency, and CH4 emission parameters and multivariate redundancy analysis identified associations between animal and dietary drivers on the same variables. Total DMI (kg/d) was higher for cows offered LFP (17.3) and MFP (17.9) compared to HFP (15.3) and FOR (13.8) (P<0.001). Milk yield (kg/d) (P<0.001), milk yield/DMI (kg/kg) (<0.001), ECM/DMI (kg/kg) (P<0.001) and milk energy/DMI (MJ/kg) (P<0.001) were higher for LFP and MFP compared to HFP and FOR. Methane/DMI (g/kg) was higher for HFP (24.3) compared to MFP (22.4) (P<0.001). Methane/milk yield (g/kg) (P<0.001) or CH4/ECM (g/kg) (P<0.001) was higher for HFP (22.5 or 21.6) and FOR (27.0 or 25.8) compared to MFP (19.1 or 17.9). There were no differences between LFP and MFP or between HFP and FOR for milk yield (kg/d), milk yield/DMI, ECM/DMI, milk energy/DMI, CH4/milk yield and CH4/ECM. Differences existed between breeds for residual feed intake (P=0.040), milk yield/DMI (P=0.041) and CH4/DMI (P=0.048) with multivariate redundancy analysis demonstrating negative correlations with efficiency and positive correlations with CH4/DMI and CH4/milk yield. Feeding concentrates at 70% to 90% of DMI (present LFP group) would not result in any further benefits for productivity, feed efficiency or CH4 yield and intensity when compared to feeding 41% to 70% concentrates of DMI (present MFP group). There may be opportunity to improve profitability for lower intensity farms with less concentrate input.