Cow Chance is similar to Pig Chance. It is simply the chance that the animal will be a cow instead of a sheep or a pig. This quality becomes available after purchasing the Extreme Gardening board. You can view your current cow chance in the bar in the lower left hand corner of the screen.
Cow chance can be increased by growing turnips. Each turnip collected increases the cow chance by 1%.
Cow chance has the following effect in the various boards:
Brickout, Starshooter, and Lawn Mowing: Each cow that falls off the screen yields $50. Comparatively, sheep yield $1 and pigs yield $5.
Animal Jumping: Cow chance does not seem to affect the DPS.