The bug
Large amounts of goats causes server performance issues. Most likely, this is because the goats are always looking for a target to ram it through. This is not done by other mobs. However, the goat do not pathfinding to water like turtles for example, which means pathfinding for target to ram is too resource-intensive.
How to reproduce
Create a world without any entities.
Summon around 300 goats.
❌ Notice how ms increases significantly, compared to turtles/sheep/cats.
Goats are even laggier than axolotls. Just about 80 goats is enough to drop 80 fps to 30 fps and bring the server to about 22 MSPT average. This is more or less the same impact that 300 axolotls have on my computer.