Expert: Walter Hintz - 12/24/2005

Question
dear Walter
it puzzles me as to why cows have four teats on their udders when all other similar mammals that I can think of which normally give birth to one, or perhaps two, young only have two teats?
I have asked many people about this, from dairy farmers to vets, and no-one has yet come up with a good reason.
Any ideas?  

Answer
Hi Julie;  Good Question.  The best explanation is that the ancestors of cows gave birth to more than one or two young and modern cows have retained extra nipples.  Actually the number of nipples in mammals varies from 2 to 19 (why an uneven number I do not know.) It is also a fact that 50% of calves born to cows even have more that 4 teats.  These are called supernumery nipples and even occur sometimes occur in people.
  Actually there is an advantage to having more nipples than young in case one of them is infected or something.