rats, mice, gerbils, hamsters i can feed off by the hundreds and thousands and never feel a slight bit of grief over it..
guinea pigs however..
i have a real soft spot for those!
i went to make a weekly rodent delivery at a petshop.. and was strolling around while they unloaded the mice and rats, and happened to peak into their small animal section.. low and behold is a BIG brown pig.. i asked if i could hold him.. they said sure..
.. about 40 seconds later i was in love LOL
long story short he was going to be snake food.. and i couldnt let that happen! so.. hes my BIG little buddy 
my sister had another resuce pig.. a female this time.. needless to say.. ive got MINI PIGS on the way! wooo LOL

the girl "oreo"

the girl "oreo"

the boy "lucky" LOL 
to answer your question..
frozen deliver as much as nutrients as needed.. as long as they are freezer burned.. freezer burn = bad! 
best of luck
dan