Enteric Methane Emission and Milk Component Profiles of Holstein and Jersey Cows: A Respiration Chamber Study.

Holstein and Jersey dairy cows differ in body size, feed intake, milk production, and milk composition, which may influence the interpretation of enteric methane (CH4) emissions. This study compared production traits, milk composition, and respiration chamber-measured CH4 emissions between 10 Holstein and 10 Jersey cows. Repeated measurements were averaged within cow, and breed differences were evaluated using independent two-sample t-tests. Sensitivity analyses additionally adjusted for age and days in milk. Holstein cows had greater body weight, dry matter intake, milk yield, fat- and protein-corrected milk, and daily CH4 production than Jersey cows. Jersey cows had higher milk fat and protein concentrations, whereas daily milk fat yield did not differ significantly between breeds. No significant breed differences were detected in CH4 production per unit of dry matter intake, milk yield, or fat- and protein-corrected milk. In the unadjusted analysis, Jersey cows had lower CH4 production per unit of milk fat yield, but the breed difference was inconclusive after adjustment for age and days in milk. Methane production per unit of milk protein or lactose yield did not differ significantly between breeds. These findings indicate that breed comparisons of enteric CH4 depend on the basis used to express emissions, while the component-specific ratios should be interpreted as exploratory animal-level measures.