If you don't want spoilers and want to figure the gameplay out on your own then don't read below! Otherwise, here is some more detailed info about this mod:

Interact with cowplant to start relationship with it
Milking, Fattening Up, Taking Cutting will affect the relationship negatively
Talking, Petting, Playing will affect the relationship positively
All interactions are tiered based on the sims relationship with the cowplant; for example a sim cannot play with a cowplant until they are at a certain friendship level, but they can pet them regardless of the relationship
Sims will pet the cowplants autonomously
When hungry or starving the cowplant can be fed free food scraps, fish, steak (costs §50), or faux meat cubes
This cowplant will take longer to become starving, and will take longer to die from starvation
The cowplant will be ready to be milked after a feeding
Sims with high relationship will be able to 'Fatten Up' cowplant by feeding it one more time, but this will effect their relationship negatively
Cowplants will give cowplant milk instead of essence, and it's quality is based on their relationship with sim
Sims can grab a glass of milk, or they can measure a cup of milk to use as an ingredient
Sour milk and cream don't have drinkable versions (yet) but they do have the option to measure a cup of it to use as an ingredient
There's a chance of getting a playful buff when a sim plays with the cowplant
If your sim eats the cake when a cowplant is starving, it will still get eaten and the cowplant will give sour milk
Sims who have a better relationship with a cowplant that eats them will have a better chance of not being drained and in turn able to getting eaten again without dying!
Sims will become terrified after being eaten by a cowplant and will not be able to interact with any cowplants
You can create chocolate and strawberry cowplants by splicing a piece of the hybrid cowplant onto the cacao tree and strawberry plant
You can find all seeds in the Appliances > Fridge section of the catalog with the bb.showhiddenobjects cheat active
You can 'Clip Tendrils' from the cowplant which will give you a new ingredient that will be used in future recipes

More to come:

New recipes
Add buffs to drinks

Known Issues:

The cowplants image in the friends panel will periodically revert to a llama icon
Sometimes your sim will cancel out of feeding a cowplant - still looking into this but I think it has something to do with with how the game prioritizes the cowplant friendship
Spliced plants don't show the name of the grafted cowplant part

Gameplay Mods

Cowplant Farming

Stockable Crates & Barrel Displays

Retail Produce Stands

Bountiful Harvest Tradition

Iced Fish Displays

Fishing Cooler

Functional Wall Epitaphs

Foraging Mod

Retail Aquarium Set

Stockable Produce Displays

Voidcritter Card & Comic Set

Foraging Tradition