Comparative analyses of enteric methane emissions, dry matter intake and milk somatic cell count in different residual feed intake categories of dairy cows
This study compared the different residual feed intake (RFI) categories of lactating Holsteins with respect to methane emission, dry matter intake (kg), milk somatic cell count (SCC, 103/mL) and β-hydroxybutyrate (BHB, mmol/L). RFI was calculated in 131 lactating Holstein cows that were then categorized into –RFI (RFI<0) vs. +RFI (RFI>0) and low (RFI<-0.5 SD) vs. high RFI (RFI>0.5 SD) groups. Milk traits were recorded in 131 cows while CH4 and CO2 were measured in 83. Comparisons of –RFI vs. +RFI and low vs. high RFI showed 7.8% (22.3±0.40 vs. 24.2±0.39) and 12.9% (21.1±0.40 vs. 24.2±0.45) decrease (P<0.05) in DMI of –RFI and low RFI groups, respectively. Similarly, –RFI and low RFI cows had lower (P<0.05) CH4 (g/d) by 9.7% (343.5±11.1 vs. 380.4±10.9) and 15.5% (332.5±12.9 vs. 393.5±12.6) respectively. Milk yield was not different (P>0.05) in –RFI vs. +RFI and low vs. high comparisons. The –RFI and low RFI cows had lower (P<0.05) SCC in –RFI vs. +RFI and low RFI vs. high RFI comparisons. BHB was lower (P<0.05) in low RFI compared to the high RFI group. Low RFI dairy cows consumed less feed, emitted less methane (g/d), and had lower milk SCC and BHB without differing in milk yield.