Longitudinal characterization of the metabolome of dairy cows transitioning from one lactation to the next: Investigations in fecal samples.

The fecal metabolome comprises metabolites that are excreted or not absorbed by the animal. This study examined the changes in the fecal metabolome of dairy cows from the end of one lactation period, through the dry period, and into the subsequent lactation. Twelve Holstein cows (BW = 745 ± 71 kg, BCS = 3.43 ± 0.66) were housed in a tie-stall barn from 7 wk before to 15 wk after parturition, with dry-off occurring approximately 6 wk before the expected calving date (mean dry-off time = 42 d). Fecal samples were taken at wk -7, -5, -1, +1, +5, +10, +15 relative to calving. Targeted metabolomics identified a total of 93 metabolites, including AA, biogenic amines, bile acids (BA), and acylcarnitines (AcylCN) and some phospholipids. Principal component analysis (PCA) revealed clear metabolic shifts that showed a clear separation between the samples from the dry period and the samples from the end, early and middle of lactation, indicating significant changes in the metabolic profiles in the feces. The transition from the dry period (wk -5, -1 relative to calving) to lactation (wk +1, +5, +10, +15, -7 relative to calving) is characterized by an increase in fecal AA and metabolites, such as Glu, Met, β-alanine, and methionine sulfoxide, reflecting a shift in nitrogen metabolism to support increased protein metabolism for milk production. Higher concentrations of polyamines, such as spermidine and putrescine, were observed postpartum, indicating increased cell growth and improved tissue regeneration. Elevated gamma-aminobutyric acid (GABA) levels during lactation indicate increased microbial activity driven by a nutrient-rich diet. Results showed significant adjustments in bile acid profiles as cows transitioned into lactation. Deoxycholic acid (DCA) remained the predominant BA in feces, reflecting ongoing microbial transformation, while glycine- and taurine-conjugated BA increased postpartum, suggesting improved enterohepatic circulation and lipid absorption. Fecal acylcarnitines showed dynamic shifts with elevated levels during late gestation, a decrease in the dry period, and an increase postpartum, indicating increased fatty acid oxidation to meet energy demands. Results showed that phosphatidylcholines decreased prepartum but increased after calving. This indicates shifts in lipid metabolism reflecting energy requirements in lactation and suggests that fecal lipid composition is an indicator of metabolic adaptations in dairy cows. In particular, PCA revealed cosiderable overlap in the fecal metabolite profiles of multiparous and primiparous cows, indicating similar metabolic profiles. This was also confirmed by volcano plots, which showed no significant differences in fecal metabolism between the 2 groups across different weeks relative to calving (wk -7, -5, -1, +1, +5, +10, +15). Overall, these results emphasize the complex interactions between dietary factors, liver and gastrointestinal function, and the gut microbiome in shaping the fecal metabolite profile of dairy cows. These results underscore the value of this data set in advancing the application of fecal metabolome profiling to investigate metabolic changes during critical transitions in the lactation cycle of dairy cows.