The Calf-Tel Indoor Pen System is designed to house dairy calves until about 60 days of age. Measuring 4 feet wide, nearly 4 feet high, and either 4, 6, or 7 feet long, the pens are made of a thermoplastic material that's resistant to moisture, microorganisms, and most chemicals and are designed to be easy to clean/sanitize to help ensure calf health. They are lightweight, free-standing, interlocking, and can be set up, expanded, or configured via solid-steel connectors. Air circulates through the pen's front and adjustable rear panels. Other features include hinged door for side access, steel-reinforced door frame, outside-the-pen bottle holder and feeding pail, and pail dividers to reduce feed waste.