
Hi Dawn,
I have large breed/fast growth dogs and both of mine were started on BARF the minute that I got them home ;-)
My male was nearly 4 months when I got him and when I got Callia 2yrs later, she was only 7 weeks when she had her first chicken wing. I did introduce gradually over a couple of days, more so because I didn't want to have a dramatic change of diet immediately other than worries about BARF. I was already feeding it to my old Shepherd though so had experience.
There are some really good books out there, have a look on Amazon. I have (somewhere) 'grow your pups with bones' by Dr Ian Billingshurst, amongst others, google him and see what comes up. And, as has been mentioned, BritBarf is excellent and really does answer most questions :-)
It's brilliant that you have a good local butcher. Where I used to live my butchers were also an abattoir and were thankful that I took away a lot of their 'waste' as they used to have to pay by the kilo for removal of it.
Incidentally, my male has just recently had lots of in-depth X- Rays done and the Vet commented that his skeleton was very strong looking with good calcium sufficiency for a large breed 6yr old.
Good luck,
Jo