Currently, butchery is an industry that annoying to manage at low numbers, and near impossible to manage when you have 10 or more pages of animals.
3 types of butchering permissions.
"Unavailable", "Slaughter when fully grown", and "Slaughter Now"
Any animals which have become their max size are and were marked as "Slaughter when fully grown" changes to "Slaughter Now"
You can slaughter baby animals manually with "Slaughter Now", which works like the current game.
New born animals are automatically marked for "Slaughter when fully grown"
Baby animals are auto assigned to the same pen as their mother when they are born.
There will be a new Workshop option 'o-W' to turn these behaviors off if desired.
To set up your meat industry. You need a breeding stock. 1 or more female and 1 or more males(only 1 of each needed). Change their butcherability to unavailable and pen them up in a large safe pen. All of their babies will be born, assigned to the same pen and butchered when they are fully grown whenever your butcher dwarf gets around to it. It may be prudent to only allow one female per pen and make the pen very large to encompass all the babies. Have one large 30x30 pen per breeding female so overcrowding won't be an issue. Make sure you save one male somewhere safe too.
You can have a large meat industry without the usual player micromanagement, similar to farming. If should keep your butchers and tanners busy full time once things get going.
These rules only apply to animals in pens. Animals not in a pen, such as free roaming dogs and cats are not auto marked for "slaughter when fully grown" They can still be set to any of the 3 slaughtering option, "Unavailable", "Slaughter when fully grown", or "Slaughter Now" manually. However, if the mother cat or dog was assigned to a pen, her babies will be marked for "Slaughter when fully grown"