Longitudinal characterization of plasma amino acids, biogenic amines, and amino acid-related metabolites in heifers from birth to first calving in response to colostrum and transition milk feeding

This study presents the first comprehensive longitudinal metabolomic profiling of plasma AA, biogenic amines, and AA-related metabolites in Holstein heifers from birth to first calving, with a focus on developmental dynamics and the influence of colostrum and transition milk (TM) feeding. Thirty female Holstein calves were enrolled. Newborn calves were fed ∼3.8 L of colostrum within 2 h of birth, followed by 1 to 1.5 L at 11.5 h postnatum. Calves were then assigned to receive either TM (6 L twice daily from dam) or milk replacer (MR; 6 L twice daily, 140 g/L) for 5 d, followed by feeding MR (12 L/d) via an automated system until weaning. Weaning was performed gradually from 8 to 14 wk. From d 14 onward, calves were group-housed in straw-bedded pens (up to 10 per pen) with access to solid feed. Blood samples were collected at different time points: 30 min after birth (before colostrum intake), 12 h after birth following colostrum intake, preweaning (wk 2, 6, and 10 of life), at weaning (wk 14), postweaning (mo 8), at insemination (13 mo), 3 wk before calving, at calving (average age of 26 ± 2.3 mo), and 3 wk after calving. Plasma samples were analyzed for AA, biogenic amines, and AA-related metabolites via liquid chromatography-tandem mass spectrometry (LC-MS/MS) using the Biocrates MxP Quant 500 kit. Volcano plot analysis (P < 0.05, fold change ≥1.5) revealed that 21 plasma metabolites were changed after colostrum intake. Sixteen metabolites increased after colostrum, including essential AA (Met, Lys, Thr, Leu), α-aminoadipic acid, and serotonin, suggesting rapid protein digestion, systemic anabolic activation, and serotonergic stimulation. Five metabolites, including creatinine, Gly, phenylacetylglutamine, and hippuric acid, decreased significantly, suggesting reduced muscle breakdown and early modulation of microbial metabolism. Maturation of kidney function may have increased creatinine excretion. No treatment or treatment × time interaction effects were observed for any of the metabolites, indicating that TM feeding did not alter plasma metabolite profiles. In contrast, significant time effects and principal component analysis confirmed that developmental stage was the primary determinant of temporal variation in plasma metabolite composition. Amino acids, both essential (e.g., Met and Lys, peaking preweaning) and nonessential (e.g., Ala, decreasing near calving), showed temporal shifts reflecting dietary changes and physiological demands. Biogenic amines and AA-related metabolites involved in one-carbon metabolism (betaine and sarcosine, decreasing postweaning and prepartum), polyamine synthesis, and nitrogen catabolism demonstrated coordinated changes. Histidine-related metabolites (carnosine, increasing postweaning) indicated muscle maturation and adaptation to oxidative stress. Tryptophan-derived metabolites (kynurenine, serotonin, and indole metabolites) highlighted immune activation and microbial maturation. Nitrogen metabolism intermediates (citrulline and ornithine, decreasing postweaning; homoarginine, increasing at calving; phenylacetylglutamine, showing transient changes) reflected urea cycle and nitrogen disposal adjustments. Other metabolites, such as γ-aminobutyric acid, taurine, and lactate, displayed patterns indicative of neuroendocrine signaling, antioxidant defense, and energy metabolism shifts throughout development. Overall, plasma AA, biogenic amines, and AA-related metabolites in heifers are primarily influenced by developmental stage rather than TM feeding, with colostrum intake triggering rapid metabolic responses.