Measuring individual carbon dioxide emissions as a proxy for feed efficiency on dairy farms - preliminary results

The costs and practical challenges of measuring individual feed efficiency on dairy farms have hampered its use both in farm management and genetic selection. The concept of residual carbon dioxide (RCO2) is similar to the index of residual feed intake (RFI), and used as a proxy, it could potentially enable ranking cows based on feed efficiency. In this study, we aimed to assess the relationship between RCO2 and RFI in mid-lactation (115 to 175 days in milk), using data of 313 cow-per-treatment observations from five experiments with individual feed intake records. Carbon dioxide production was measured by GreenFeed units. Residual CO2 (kg/day) and RFI (kg of dry matter/day) were estimated using a mixed model approach. Three cow groups (high/mid/low) of equal sizes were created both for RCO2 and RFI. Cows in the high-RCO2 group produced 1.92 kg/day (95% CI: 1.78 – 2.06, P < 0.0001) more carbon dioxide than their low-RCO2 herd mates. At the same time, high-RCO2 cows had 1.31 kg/day (95% CI: 0.95 – 1.67) higher RFI compared to their low-RCO2 counterparts (P