Feeding 2-fold upconcentrated versus native colostrum modulates systemic immunity, metabolism, and fecal profile in neonatal calves

This study investigated the effects of feeding a 2-fold upconcentrated, vacuum-dried colostrum replacer (HC) compared with pooled native colostrum (NC) on passive immunity transfer, early metabolic adaptation, and fecal composition during the first week of life. Twelve Holstein calves were enrolled at birth and assigned to HC (n = 6) or NC (n = 6). Calves received either 2.5 L HC or NC at 4 and 12 h postpartum (p.p.), respectively, followed by transition milk until d 3 p.p. and bulk tank milk from d 4 p.p. onward. The HC replacer was formulated from the same pooled colostrum batch as the NC and adjusted to provide approximately twice the concentrations of major milk components (fat, protein, and lactose). Blood samples were collected at 4 h p.p. before the first colostrum feeding, and subsequently at 12 and 24 h p.p., as well as daily from d 2 to 5 and at d 7 p.p., always immediately before the morning feeding and analyzed for IgG, activity of gamma-glutamyl transferase, total protein (TP), glucose, lipid metabolites, nonesterified fatty acids, and urea; apparent efficiency of absorption of IgG was determined at 24 h p.p. (i.e., 20 h after the first colostrum feeding). Fecal samples (meconium and daily samples collected during d 2-7 p.p.) were analyzed for glucose, IgG, triglycerides, and short-chain fatty acids (SCFA). Growth and rectal temperature were recorded daily. The HC calves achieved greater serum IgG concentrations at 12 h p.p. and maintained greater IgG and TP throughout the first week of life. Despite the markedly higher nutrient and fat supply provided by HC, serum triglyceride, phospholipid, and cholesterol concentrations did not differ between groups, whereas HC calves exhibited greater glucose concentrations at 24 h p.p. Calves receiving the HC treatment exhibited greater BW gain and higher ADG during the first 7 d p.p., indicating improved early growth performance. Fecal analysis revealed treatment-dependent differences in nutrient passage. The HC calves had higher fecal glucose and IgG concentrations. Among the quantified SCFA, only iso-valeric and n-butyric acid concentrations differed between groups, with higher values observed in the HC group. Overall, feeding an upconcentrated colostrum replacer enhanced passive immune transfer and early energy status without altering circulating lipid metabolites, as well as partially affecting fecal composition and SCFA profiles.