Effect of proportion of pasture in the cow diet and seasonality on the milk metabolome as determined by H-NMR.

This study investigates the effect of varying proportions of pasture (high, medium, no-pasture) in the diet of cows and seasonality on the milk metabolome throughout lactation using proton nuclear magnetic resonance (H-NMR) spectroscopy. This study explored the potential to differentiate milks from varying levels of pasture in the cow's diet and highlight potential biomarkers for authentication. A total of 54 spring calving cows were assigned to the 3 diet treatments for the duration of lactation. Weekly bulk milk samples were collected from each herd. Over 37 wk (March-November 2020), 43 metabolites representing diverse chemical classes, including AA and nitrogenous compounds, carbohydrates, VFA, organic acids, and alcohols were quantified. Significant dietary and seasonal influences on the milk metabolome were characterized, with signature differences attributed to the proportion of pasture in the cow's diet and the season of milk production. Receiver operating characteristic analysis of the milk from different feeding systems across lactation highlighted the potential of the milk metabolome to distinguish pasture from nonpasture-derived milks, with a series of metabolites demonstrated as excellent biomarkers, including hippurate. Multivariate analysis also highlighted dimethyl sulfone as a key metabolite for the distinction between different diet regimens. These findings highlight the diversity and complexity of the composition of milk as affected by seasonality, and signature characteristics that are associated with pasture-based feedings systems. As "grass-fed" dairy products become more prominent on the market, the analysis of the milk metabolome using H-NMR shows significant promise for utilization as a tool for authentication purposes.