Calves have rennin in their true stomach to coagulate milk protein and slow down rate of passage. They also have pepsin to digest protein with lactase and lipases in the small intestine to digest lactose and milk fat. Enzymes to digest more complex carbohydrates and feeds develop within two to three weeks after birth to digest calf starter and milk replacers containing non-milk sources of nutrients.
To add to Mike's comments, calves have high levels of HCl and rennin in the stomach at birth and can digest large amounts of casein and milk fat for this reason. Shortly after birth other proteases and carbhydrases are present in the small intestine. These are present in samll amounts right after birth and increase rapidly within 12 hours.
Mike Hutjens, Extension Dairy Specialist, University of Illinois - Illini DairyNET
Arlyn Heinrichs, Dairy Extension, Penn State University.
