Colostrum should be thawed in a warm water bath (50°C or 120°F), and NOT at room temperature on a counter. Microwaving on low for short time periods is acceptable. Avoid creating hot spots in the frozen colostrum.
Preventing Bacterial Contamination and Proliferation During the Harvest, Storage, and Feeding of Fresh Bovine Colostrum
Freezing and Thawing Colostrum
A Guide to Colostrum and Colostrum Management for Dairy Calves