Parity and dietary energy regulate IgG and non-IgG bioactive proteins in colostrum of beef cattle.

Bovine colostrum provides crucial immune and developmental support to newborn calves, yet the roles of non-immunoglobulin bioactive proteins remain underexplored. The objective of this study was to characterize the colostrum proteome and evaluate the effects of parity, prepartum dietary metabolizable energy, and colostral immunoglobulin G (IgG) concentration on its protein composition. Colostrum samples from primiparous and multiparous Angus × Simmental beef cows fed low-, control-, or high-metabolizable-energy diets during the prepartum period were analyzed by quantitative proteomics. We identified distinct proteomic signatures influenced by both parity and dietary energy. Colostrum from multiparous cows consistently exhibited an immune profile characterized by higher levels of lactoferrin, β2-microglobulin, and other immune-related proteins, particularly when fed diets high in metabolizable energy. In contrast, primiparous colostrum was enriched in structural and developmental proteins (e.g., tripartite motif-containing protein 68, growth/differentiation factor 8), with immune-related proteins increasing only under high-energy conditions. Colostrum from cows with higher IgG concentrations also contained proteins involved in innate immunity, cytoskeletal remodeling, and calcium signaling. In contrast, low-IgG colostrum showed compensatory enrichment of transcriptional and metabolic regulators. These findings reveal the interplay among parity, energy intake, and colostrum bioactivity, suggesting that cow parity and nutritional strategies should be considered to enhance colostrum quality and improve neonatal health outcomes.