While both bockwurst and bratwurst can be made from either pork or veal, bratwurst is almost always pure meat, while bockwurst is expected to incorporate green onions, leeks, chives and other vegetables. Bratwurst can also be prepared fresh or smoked, while bockwurst is widely known for being made from finely ground ingredients that are usually served fresh to preserve flavor.
The single biggest difference between bratwurst and bockwurst is their respective use of only meat and a mixture of meat and vegetables. Bratwurst also has a broader range of flavors from which to draw while bockwurst is nearly almost mild in its palette.
Bockwurst sausages are very nearly all white or pale, while bratwurst may differ in coloration but hews toward darker colors reflecting its meaty makeup. Bockwurst sausages are also uniformly plump in outline, while bratwurst can be leaner, at least relative to the former type of sausage.
Bockwurst, because of its plumpness and its reputation for using fine-ground meats, is made from meal much more commonly than bratwurst is. The smooth texture of ground veal helps bockwurst maintain its uniform surface and its smooth feel when bitten into and chewed. Bratwurst is rougher and heartier, its German name literally translating to "farmer's sausage."