Well we reckon that our cades are the equal to the lambs on ewes, right to the moment they are weaned, then it is toss up which keep going strongly... Some who eat pellets well, will do OK.It's a simple job which people try to be smart at and over complicate - usually because the College has told them so
Once they're a week old it's a waste of time giving hot/warm milk IME - and you run the risk of Red Gut.
The milk stays fresher for longer cold so yes there's bound to be less bugs
I used to feed warm until they were weaned off it and lambs always looked shyte and we're here til well on in the year. Can't remember when I switched to the method of rearing above but since, the pet lambs go away mixed with the rest of the lamb crop and can't be picked out coming off the trailer at market or abattoir