The protein composition and digestive characteristics of four commercially available infant formulae (IF) manufactured using bovine (B-IF), caprine (C-IF), soy (S-IF), and rice (R-IF) as a protein source were examined in this study. Plant-based formulae had significantly higher crude protein and non-protein nitrogen (NPN) concentrations. Static in vitro gastrointestinal digestion of these formulae, and subsequent analysis of their digestates, revealed significantly higher proteolysis of B-IF at the end of gastrointestinal digestion compared to the other formulae, as indicated by the significantly higher concentration of free amine groups. Furthermore, differences in structure formation during the gastric phase of digestion were observed, with formation of a more continuous, firmer coagulum by C-IF, while R-IF demonstrated no curd formation likely due to the extensive hydrolysis of these proteins during manufacture. Differences in digestive characteristics between formulae manufactured from these different protein sources may influence the bio-accessibility and bioavailability of nutrients, warranting additional study.