Thaw them over night (24 hours if you want exact measurements) in a refrigerator (most refrigerators are roughly 36 degrees F) then before feeding put them in a container containing the hottest your tap water will get and let it warm for 30 minutes. Halfway through that 30 minute time frame (that is at the 15 minute mark) drain and refill the container with again, the hottest your tap water will get. This will get the rodent to the desired temperature.