How many cows are there in the world?
According to the related link below, the FAO estimates that there were 26.5 million dairy cows in the world in 2010. The statistic for number of beef cows in the world is more vague, because beef cows are lumped in with the "cattle" category, not individually as female mature bovines.
There's many farmers in the world that don't have cows, but of course this depends on where you live. If you're in a second- or third-world country having a cow or a herd of cows is a sign of prosperity. Otherwise, cattle are great for meat, milk, draft work, and for keeping the grass down around the hut or house or pasture.
This is an impossible number to obtain, because cows get bred and calve out every day in the US. One day there may be 4 million cows that are bred, the next there may be only 200,000 that get bred. And each year that a statistics is taken of how many cows get bred in the US, each year it will be very different from the next.