Age and Post-Prandial Variations on Selected Metabolites in Dairy Calves Fed Different Liquid Diets

SIMPLE SUMMARY: The aim of this study is to evaluate the age and post-prandial variations in selected metabolites’ concentration during the preweaning period, which may indicate a shift in metabolism, from pre-ruminant to a functional ruminant, according to the liquid diet (whole milk or milk replacer) fed to dairy calves. An additional goal was to evaluate fructosamine concentrations as a replacement for glucose to better understand the glycemic status and possible use of it as a biomarker of rumen development. Plasma glucose concentration did not differ between the liquid diets. The sampling time to study the glycemic status varies with the liquid diet. The best collection time is 1 and 4 hours after being fed whole milk or milk replacer, respectively. Fructosamine was not informative for an indirect evaluation of ruminal development. ABSTRACT: The aim of this study was to evaluate the age and post-prandial variations in selected metabolite concentration that may indicate a shift in metabolism, from pre- to functional ruminant, according to the liquid diet fed to dairy calves. Sixteen newborn Holstein calves were included in the study in a randomized complete block experimental design. The calves were individually housed and fed 6 L/d with whole milk (WM) or milk replacer (MR). Blood samples were collected weekly at 0 h (before feeding), 1 h, 2 h, 4 h, and 8 h after morning feeding to evaluate glucose, β-hydroxybutyrate (BHB), fructosamine, total protein, and albumin. Calves fed WM had higher performance (p < 0.01) than did calves fed MR. The different liquid diets did not affect the average concentrations of plasma glucose. However, BHB was higher for WM-fed calves (p < 0.01). The concentration of plasma glucose reached the highest concentration at 1 and 4 hours after feeding WM or MR, respectively. Thus, these would be the most appropriate sampling times to study the glycemic status of calves according to the liquid diet fed. Fructosamine did not prove to be an informative metabolite to understand the shift in metabolism, as a function of rumen development, due to a small reduction as a function of age and a sampling time effect.