Impact of timing of a second colostrum feeding on serum immunoglobulin G dynamics in calves during the first week of life

This study evaluated whether a high-IgG colostrum replacer administered at 24 h postpartum (p.p.) influences IgG absorption in neonatal calves. Twelve Holstein and crossbred calves were assigned to 2 groups: CCT (n = 6) received 2.5 L of colostrum replacer (100 mg IgG/mL) at 4 and 12 h p.p., followed by enriched bulk tank milk at 24 h p.p.; CTC (n = 6) received the same colostrum replacer at 4 and 24 h p.p., with enriched bulk tank milk at 12 h p.p. Enriched bulk tank milk was bulk tank milk supplemented with 27 g/L colostrum replacer, mimicking transition feeding. Serum IgG, total protein, γ-glutamyl transferase, and apparent efficiency of absorption (AEA) were measured. The IgG concentrations and AEA were compared at 24 h p.p. in CCT and on d 2 (32-38 h p.p.) in CTC to reflect the status after the second colostrum feeding in each group. At these time points, CTC calves had lower IgG (16.9 ± 1.1 vs. 23.3 ± 1.8 mg/mL) and AEA (11.7% vs. 16.8%), although IgG persisted longer. These findings clearly highlight the superiority of early colostrum feeding for achieving adequate passive immunity, while also revealing that lower initial IgG concentrations were accompanied by a relatively greater persistence during the first week of life.