The ileum is a key site for immune development in a newborn calf, and this study looked at what happens to that development when first colostrum feeding gets delayed. Using transcriptome analysis, researchers tracked gene expression changes in the ileum tied to immune function, comparing calves fed right away against calves with a delayed first feeding. For producers who sometimes can't get to a calf immediately, this adds tissue-level evidence to what delay actually costs beyond the passive transfer number.
"Transcriptome analysis revealed that delaying first colostrum feeding postponed ileum immune system development of neonatal calves" — Y. Song, H. Sun, Z. He, A. Fischer-Tlustos, T. Ma, M. Steele, L.L. Guan. Genomics. 2021;113(6):4116-4125.