Made with beef, it won't be traditional demi-glace, but it will be something good to eat. For example, I don't think I'd use concentrated beef stock on chicken or fish, as one does use a veal demi-glace. I'm sure your recipe has a pig foot. That has a great deal of gelatine.

I don't have demi-glace advice. But may I ask a question: Isn't veal the same as beef?

Chicken feet would also be a good suggestion. You're going to have more total flavor with chicken based stock... which might not be what you want with a normally veal stock.

You could always just add some powdered/sheet gelatine to your stock. That seems to be Cooks Illustrated's weapon of choice these days.

kristab, yes, veal and beef are the same animal, but there are differences in how the two are raised and the age at which they're slaughtered that bother some people.

You could try using oxtail, which has a fair amount of collagen in it and fewer of the ethical concerns of veal.

use pork bones instead of beef will make almost as good a demi glace
alot of restaurant who still make stocks use pork and chicken bones due to the cost of veal bones

I would use oxtail and neckbones, which I always use when making any kind of beef stock.

I will third pig feet. I once made a pig's foot in stock dish for a picnic, which I'd chilled well for safety reasons. When I opened it up, it was solid - not solid like Jell-O, but solid like, well, it bounced when poked.

I've done chicken feet, too - they don't have much flavor, but they do have a fair amount of gelatin as well.

Oxtail and neck bones are great suggestions if you're trying to maintain a strict adherence to a bovine based demi. I suggest a split cow's foot as well.