There are scientists that are convinced that cows do predict precipitation, and other that are sure they can’t.
There is evidence on both sides, but unfortunately there’s still no conclusive answer.
Cows do definitely spend more time on their feet when the weather is warm and dry. This help them lose heat, as it increases the amount of skin exposed to air and allows the blood to cool down, whereas lying down slows this heat loss. Overheating means a cow has to spend more time panting and less time eating, so keeping cool is an important issue. Before a bout of rain, the atmosphere’s pressure drops and signifies the temperature is about to plummet too. So cows could be able to detect changes in temperature that just happen to coincide with impeding drizzle.
Evidence from dairy farmers suggests that lying down is what a cow does when its chewing cud. Many claim there is no relationship between a cow’s behaviour and a downpour and that this saying is nothing more than an old wives’ tale.
Image from www.flickr.com/photos/stuutje