Weaning age for mammals?

[Kerenza]

I was wondering if anyone knows what determines weaning age in mammals?

[GDG]

I don't know if there has been a scientific study of the question, but here are the factors that I would guess go into it:

• Nursing is an investment (and substantial energy drain) for the mother, requiring the mother to eat and drink more than she would otherwise need. Thus, weaning as early as possible is best for the mother. However,
  
• it takes some time for the neonate's digestive system to be ready for "regular food". For example, the digestive tract is typically colonized with bacteria (some of which aid in digestion), the jaws and teeth need to mature to some point, etc. Milk provides a high-calorie, easy to digest food until the newborn's digestive system is ready.
  

Given that, my guess would be that weaning occurs when the child has developed to the point where it can digest food other than milk. In humans, my guess is that the coordination necessary for chewing and swallowing solid food is the rate limiting step. In cows, probably the colonization of the rumen.