With the update on 28 August 2018, strawberry, vanilla, and chocolate cows replaced all regular cows in RuneScape (except Zanaris) as a teaser for player-owned farm. They were removed upon the release of the player-owned farm.
During Double XP Weekend (31 August to 3 September) seven special farm animals were also available to spot around RuneScape. Doing so awarded a small experience lamp for each of them. The animals were intentionally made available again during each Double XP Weekend since the one preceding the release of player-owned farm. The animals were not available during the 3 May 2021 - 24 May 2021 Double XP Live.
Finding an animal prompted the message:
You've found X/7 special farm animals. Keep an eye out for more.
The animals wandered around a general location and disappeared after being clicked on, similarly to spotting the raven in Prifddinas. Finding all seven animals awarded an additional large experience lamp and prompted a dialogue box from Granny Potterington inviting the player to the farm: Thanks for finding them all for me, these little blighters really like to cause me trouble. You seem like a handy sort, pop by my farm sometime and say hello. -Granny Potterington.