High quality corn silage and alfalfa are often used for feeding dairy heifers. These can work well for young heifers up to ~8-12 months of age depending on forage quality. However, pregnant dairy heifers have lower energy needs than younger dairy heifers and feeding the correct diet energy is important to control weight gain.
In the 2018 March Midwest Forage Association Focus on Forage article Alternative Forage Options for Heifers, UW-Extension/UW-Madison Department of Dairy Science Dairy Management Specialist Matt Akins describes options for heifers regarding forage and nutritional needs.
For more information regarding dairy replacements, please visit UW-Extension Dairy Calf & Heifer.