Untargeted Metabolic Profiling of Rumen Fluid and Milk in Lactating Dairy Cows Affected by Subclinical Ketosis

Ketosis metabolic research on lactating dairy cows has been conducted worldwide; however, there have been very few Korean studies. Biofluids from lactating dairy cows are necessary to study ketosis metabolic diseases. This study aimed to elucidate metabolic profiles of lactating Holstein cows by using proton nuclear magnetic resonance spectroscopy and to compare the healthy (CON) and subclinical ketosis (SCK) Holstein groups. Six Holstein cows were divided into two groups (CON and SCK groups). Rumen fluid and milk samples were collected using a stomach tube and a pipeline milking system, respectively. Metabolites were determined using proton nuclear magnetic resonance (NMR) spectroscopy and they were identified and quantified using the Chenomx NMR Suite 8.4 software and Metaboanalyst 5.0. In the rumen fluid of the SCK group, butyrate, sucrose, 3-hydroxybutyrate, maltose, and valerate levels were significantly higher than in the CON group, which showed higher levels of N,N-dimethylformamide, acetate, glucose, and propionate were significantly higher. Milk from the SCK group showed higher levels of maleate, 3-hydroxybutyrate, acetoacetate, galactonate, and 3-hydroxykynurenine than that from the CON group, which showed higher levels of galactitol, 1,3-dihydroxyacetone, -glutamylphenylalanine, 5-aminolevulinate, acetate, and methylamine. Some metabolites are associated with ketosis diseases and the quality of rumen fluid and milk. This report will serve as a future reference guide for ketosis metabolomics studies in Korea.