Delaying that first colostrum feeding doesn't just cost antibody absorption, it changes what's colonizing the gut in those early hours too. This study compared calves fed colostrum right after birth against calves with a delayed first feeding, tracking both passive transfer status and gut bacterial populations. For producers who sometimes can't get to a calf immediately after calving, this quantifies what that delay actually costs beyond the passive transfer number everyone already watches.
"Effect of delaying colostrum feeding on passive transfer and intestinal bacterial colonization in neonatal male Holstein calves" — A.J. Fischer, Y. Song, Z. He, D.L. Haines, L.L. Guan, M.A. Steele. J Dairy Sci. 2018 Apr;101(4):3099-3109.