Hi,Leelee.
I'm Jo,Mum to 6,expecting Seven in May.
Your baby still needs to be drinking formula if not breastfeeding.It contains the extra nutrients they need you can't get from cow's milk.What's he been drinking up till now?
When I've changed my babies' milk,whether it's from breast milk to formula or changed the formula at 6 months or when I changed to cows milk at a year,I always changed maybe 1 oz of an 8 oz bottle one day,then 2 the next day,just gradually so they don't notice the sudden change in milk.
One of mine refused bottles altogether and went straight onto a beaker at 7/8 months as she'd never had a bottle before.I've also had three of them refuse to drink out of any bottle but their particular favourite.
Keep trying,babies often take a while to get used to new things.If you're worried how much milk your little one's getting you can give dairy products,but he still needs to be drinking about a pint,you'd need a lot of dairy to make that up.See your health visitor if you're still worried.