My brother and I own the town Braircliff, we recently got mob spawning. One of our citizens spawned some chickens, cows, and sheep in our farm. We reproduced them many times and had a lot of animals. Later in the day there was some lag and ALL of them vanished. The person who spawned them had a farm also, and his animals were gone too. Help please, it took a lot of work! Thanks you!
/butcher was most likely used by the staff, which kills off all of the mobs that are in the world it is used on. This is a pretty common thing and I believe its done to reduce server lag.
Unfortunately mobs cause lag and killing the hostile mobs first and then if still laggy killing the passive mobs next usually fixes the lag. I stopped raising animals for this reason.
I'm guessing butcher is used a couple of times a day. There is no set time for it... Once people spawn enough mobs and don't harvest them, the server lags and we need to butcher. :/