Methane and carbon dioxide production from dairy bulls selected for divergent enteric methane emissions per unit of feed eaten and that from their daughters.

Enteric methane emissions can be measured on male and female cattle, unlike traditional dairy production phenotypes where a sire's breeding value is estimated from the performance of his female relatives. It is, however, important to validate that young dairy sires are a good model for female dairy animals, by confirming that phenotypic differences in CH4 emissions in bulls are observed in their daughters. Methane emissions and DMI were measured in a population of young dairy bulls (n = 486) in an indoor feeding trial for 5 wk. An estimated CH4 breeding value (metEBV) of CH4 production adjusted for the genetic variance of DMI was created and used to select 25 high metEBV and 25 low metEBV bulls to sire a cohort of heifers. The mean metEBV of the high and low sire groups, respectively, were 1.3 and -1.4 g CH4/kg DM. There was a phenotypic difference in CH4 yield of ∼8 g CH4/kg DM; although the sire groups had a similar DMI, the low metEBV sire group had lower daily CH4 production than the high metEBV sire group. A population of 393 daughters of high and low metEBV sires were subsequently measured for DMI and CH4 production in an indoor feeding trial for 5 wk in 1 of 4 lots between 9 and 15 mo of age. The nonlactating heifers from low metEBV sires produced less methane per day, with a similar DMI compared with the nonlactating heifers from high metEBV sires. Furthermore, the daughters of low metEBV sires had a lower CH4 yield (∼0.8 g CH4/kg DM per day) compared with the daughters of high metEBV sires. This dataset provided further opportunity to explore phenotypic relationships between CH4, CO2, and DMI to scope proxies for future phenotype collection. Carbon dioxide production was investigated as a proxy measure for DMI, and the ratio of CH4 to CO2 was also calculated as a trait to be investigated as a proxy for CH4 yield. A strong phenotypic correlation between CO2 and DMI, and the CH4 yield and CH4: CO2 ratio was identified for both sires and daughters, which requires further investigation in a larger dataset, but suggests these could be suitable proxies. Further research is required to measure the CH4 emissions of these daughters during their first lactation, to confirm the phenotypic differences between the daughters of high and low metEBV are observed during lactation.