A newborn calf's gut isn't ready to do much on its own at birth, it needs help getting there fast. This study compared calves fed straight colostrum for three days against calves fed a 1:1 colostrum:milk mixture, looking at how each approach shaped small intestinal development along with a couple of related hormone markers tied to gut growth. For producers weighing how much colostrum to feed versus stretching supply with milk, this gets at whether that tradeoff costs the calf anything on the development side.
"Feeding colostrum or a 1:1 colostrum:milk mixture for 3 days postnatal increases small intestinal development and minimally influences plasma glucagon-like peptide-2 and serum insulin-like growth factor-1 concentrations in Holstein bull calves" — J. Pyo, K. Hare, S. Pletts, Y. Inabu, D. Haines, T. Sugino, L.L. Guan, M. Steele. J Dairy Sci. 2020 May;103(5):4236-4251.