Re: Weaning and formula use
Since breastmilk has slightly more calories/oz than formula, it makes sense that you'd need to feed baby a little more formula than breastmilk. However, the key word here is "slightly"- see http://kellymom.com/nutrition/milk/milkcalories/ for a side-by-side comparison- so I don't think you need to start giving 8 oz bottles! I know a lot of formula-feeding moms do give their kids HUGE bottles and I think that is more for convenience, because mom won't have to give another bottle as soon, and also because formula-fed kids get used to consuming the maximum every single time they eat and can end up with tummies that only feel satisfied with the largest possible meal. Since you've nursed your baby for so long, I don't think you're going to need to give her huge bottles. Just try to read her cues- if she seems satisfied with 4-5 oz, she probably got plenty to eat.
I don't think you absolutely need to give water. AFAIK, water has been recommended for formula-fed babies for 2 reasons: first, because babies who are bottle-fed from birth often overeat and water fills their tummies without adding calories, and second, because formula sometimes causes constipation, and water helps with that. So I'd give water only if your baby is getting stopped up.
Take all this advice for what it's worth- I only had to use formula for a few weeks with my first baby and I don't know much about formula and older babies.
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