I should add that i know it sounds weird that you should feed chicks layer pellets and not keep them on straight chick starter.. but when you think about it it makes sense..
the layer pellets have more calcium which the growing chicks need ,... especially for the leg growth
the chick starter...
That's what the ranchers here found out when they were mass producing emu and ostrich for the meat industry
At first since the breeding birds were so expensive to purchase ($ 25,000 for an adult at auction was the norm) they used commercial diets... they had a lot of failures when it came to...
Mazuri makes exotic animal feed, so I know they have a ratite product line.
Most people mix up their own feeds though since the Mazuri feed has been found to be a bit lacking.
What age Ostrich are you trying to find food for?
Here in Texas the general consensus is to feed ratite chicks...