Depends on aircraft type. Most narrow bodies don't have heated lower-decks, relying on indirect heat from the main-deck. This will result in the holds being around 2-10 degrees C, but there is no way of regulating the temperature.

For wide-bodies it's different, and as a general rule one of the holds (most often the FWD) will have heating/cooling and a way of regulating the temperature. This can result in the hold being able to maintain a temperature anywhere between 5 and 25 degrees C.

All of the above are in rough numbers, as it's very much aircraft type specific. Temperature control may also be an optional extra on a given aircraft type, making it even more difficult to supply a definitive answer.