Most know that calves are not born with any immunoglobulins, which are critical for the health of a new born calf. Immunoglobulins are supplied by the cow via colostrum, or first milk, and calves only have a 24 hour window to ingest these molecules through the lining of their gut before that window closes.
During his presentation at the 2020 Ohio Beef Cow/Calf Workshop and excerpted in the 2 minute video below, Dr. Francis Fluharty further explains why a calf must receive adequate colostrum within the first 24 hours of life.