IDK if this is still of interest or has been solved elsewhere already, but since the boar/wolf breeders that initially popped up in Valheim were broken by some update a while ago, I decided to play around today and try to make a new version that works on the current patch of the game (and hopefully future ones as well).
I found out that the piggies and wolf cubs start sliding slowly whenever they stay still on a 45° normal roof piece (not rly working on the darkwood roof), while the grown boars/wolves don't do so.
I built two breeders based on this principle, with the same, simple core design but differing staircases for feeding access etc. (I prefer the one on the boar breeder, won't show the wolf one). The lower edges of the wood pieces are 12m above ground.
For feeding u walk against the 1m wood beam that separates the feeding platform (where the red mushrooms lie) from the workbench platform and throw ur food against the right half of the upper wall which ur facing (the upper 1×1 wood wall on the right side of the feeding platform in the pic) . I added a roof later to avoid weather damage.
Regarding performance: According to my testing with 2-star wolves and boars the breeders work great! As always it's a hassle to get ur beasts up there… Also from time to time a cub/piggie might decide to walk around a bit more and thus take a while longer to slide and fall, but I've successfully bred an army of around 50 2-star wolves (as well as about 20 2-star boars already) without any effort apart from feeding!
Let me know if this is helpful. Peace <3
Source: https://www.reddit.com/r/valheim/comments/sxchly/functional_boar_and_wolf_breeder/
