What plants should I be cutting in pens?

[Crowbot]

Trees? I'm trying to maximize the nutrition of a pen instead of just constantly expanding it.

[Jaggid Edje]

That's a broad question.

It would depend on if you also have a growing zone inside the pen as well, and if you want to cut "anything" that has less growth/nutritional value than what you are planting, or if you are just letting natural flora flourish in the pen and just want to cut things that have no nutritional value.

Definitely cut trees.
Beyond that, the nutritional value of animals eating growing things is not the same as what you get when harvesting, so pretty much all of the wild grasses, bushes, etc. work for grazing.

Personally, I like to maximize the growth of what they graze on in my main animal pen, so I don't need it to be so big, so I plant grass. I have a mod that let's me plant grass...absent mods I'd plant dandelions (which has the same growth stats).

Some people don't like to do this though, claiming their growers constantly run over just to plant a single dandelion each time they are eaten. I personally don't see that happening. But there is also now a mod as well that allows you to set a grow zone to "no petty jobs" so growers won't go plant in a field until x% of sowing is available to be done.
https://steamcommunity.com/sharedfiles/filedetails/?id=2619652663&searchtext=smart+farming

I also just typically leave the pen gate open and let the animals run completely free in my walled-in compound area where there is a lot of wild growth. Free Range eggs taste better.

[Jaggid Edje]

I should mention, an effective strategy if you DON'T have a grow zone inside the pen don't want to constantly be expanding the size of a pen, is to have more than one pen and just let your handlers do their jobs. They will move animals between pens automatically to balance plant growth with what is being eaten.

Another strategy is to have a pen, with fences and gates inside the pen...basically subdividing it into multiple pens connected with gates. Put the pen marker in just the middle sub-pen.
Then just rotate which gates you hold open. That way there are always penned areas growing without being eat, but there's no need to move animals around...merely clicking a button on gates every once in a while moves around where the animals will be grazing. I do this for the large areas within my walls where I let them roam.

[The Manual]

In addition to what Jaggid said, I would suggest you to not rely so much on grass and plants growing in a pen. It's a forcing to build a huge pen or -as said in previous posts- to use growing zones where you constantly have to plant grass to constantly feed your livestock. But Jaggid has explained this very well, so nothing to add about it.

Instead, my suggestion is to rely on Haygrass. You design a rather large growing zone and grow hay. Inside your pen, build several storage shelves (like animal feeders) and store hay inside them.

Obviously, still keep natural grass inside your pen, that's just a good thing, and cut trees and what your livestock can't eat. But I think haygrass works great and better due to its grow days/yield ratio.

[Jaggid Edje]

I agree with the above. While I use all the grazing techniques I mentioned, I also grow haygrass in one field where they can't get to (because haygrass is WAY more efficient when harvested compared to letting them graze it) and supplement the grazing with hay.

No way I want my pens as big as they'd need to be if I didn't supplement grazing with haygrass.

Edit to add: Also, if you are located somewhere that outdoor growing is limited (due to climate or space), animals will also eat pemmican, kibble, even meals. In addition to the hay, I have one kibble stockpile square in their pen, because I turn all the insect meat I get into kibble.

[gimmethegepgun]

Originally posted by The Manual:

But I think haygrass works great and better due to its grow days/yield ratio.

The bigger reason to use haygrass grown outside of the pen instead of dandelions inside is the issue of pawn labor. Unless you're micromanaging it by disabling sowing in the fields, what will happen with dandelions is that the animals will eat a few and then your pawns will run over to plant new ones and then go do something else. This causes them to spend a lot of time running around instead of doing something useful, whereas planting a big plot of haygrass will have them deal with the whole thing at once (or try to, anyway, it depends on how big it is and how good they are) with a minimum amount of time spent running around. Then they'll go and harvest it, again all at once, and haul it around (which, admittedly, is time spent that isn't needed with dandelions, but there's much more nutrition involved in each trip than dandelion planting trips)

[Jaggid Edje]

Originally posted by gimmethegepgun:

Unless you're micromanaging it by disabling sowing in the fields, what will happen with dandelions is that the animals will eat a few and then your pawns will run over to plant new ones and then go do something else.

Owlchemist's Smart Farming mod prevents that, by allowing you to set specific fields to not get sowed until a specified % of sowing is needed. Using it, pawns won't go to the pen to sow until there's more sowing to be done than just a few tiles.

[dnrob7]

I make a stockpile square for kibble. Haygrass and insect meat.

[Crim]

Grazing is nice, but there is no grazing in the Desert and we decided to be Ranchers!

Basically, that whole mechanic is useless for us Desert Ranchers, which is why its crucial for us to stock up food inside a small room inside the pen.
So, that it doesn't deteriorate

[Azrak]

Originally posted by Talamare:

Grazing is nice, but there is no grazing in the Desert and we decided to be Ranchers!

Basically, that whole mechanic is useless for us Desert Ranchers, which is why its crucial for us to stock up food inside a small room inside the pen.
So, that it doesn't deteriorate

Shelfs prevent them from deteriorating as well

[Kittenpox]

Originally posted by Talamare:

Grazing is nice, but there is no grazing in the Desert and we decided to be Ranchers!

Basically, that whole mechanic is useless for us Desert Ranchers, which is why its crucial for us to stock up food inside a small room inside the pen.
So, that it doesn't deteriorate

Using a Shelf will also prevent that deterioration from being outdoors. And with Kibble having no use-by date, it's a particularly useful way to feed your animals if your animals don't need a barn. :-)

Though if you're farming chickens, for example, they won't survive a cold winter - and I presume the same is for hot summers* - so it would make sense if you do need a building. I'm just mentioning that it's not absolutely necessary for animal-food storage. :-)

(* I favour cold biomes myself, and so don't have much experience with deserts.)