This depends on the cow and what the cow is feeling. Mothers or calves that have been freshly weaned from each other will call (or moo) constantly for about a week. Females that are in heat may call more frequently throughout the day.
"Moo cows" are, essentially, cows that moo.
With dairy cows, yes. Other times cows (including beef cows) will moo when they are calling to their calves, or when it's feeding time, or even when they're in heat.
yes all cows moo.
Yes.
No.
They have a stuttering problem
moo moo cows that are weird
Yes but only if its loud moo
Yes.
No, not usually.
Frogs don't moo because they aren't cows!
Cows will moo when they are separated from the herd and trying to get back to it, are looking for their calf and trying to get in contact with it if they lost it, when they're hungry (sometimes), or in challenging rivals (bulls) or new strangers to the herd. But mostly cows will moo whenever they feel the need to.