I would agree with Kathy D.  But I would also point out that a baby
breastfed for six months can go to homogenized milk at six months, not
formula, if he is also getting a variety of solid foods.  And why cannot the
mother continue breastfeeding to a year?  Or longer, if she could go 6
months full, or 12 months half time?  Now what happens to this question if
your strictly breastfeeding baby at 6 months refuses formula?  It happens
often enough.  Most formula tastes like a stale belch, at best, and any baby
who has been breastfeeding exclusively for 6 months will usually not touch
it.

A variation on this question is:  Which is better, exclusive breastmilk
feeding (by bottle or cup) or partial breastfeeding and partial formula
feeding.  That's a harder one, I think.  I would say the younger the baby
the more important the exclusivity of breastmilk feeding is.  But once the
baby is older, breastfeeding, the act of breastfeeding, or the relationship,
becomes more and more important, and probably there is some age, when
breastfeeding is *more* important than exclusive breastmilk feeding.

Jack Newman, MD, FRCPC