The "cow lobby" is large multinational corporations... so yes it's an issue beating their lobbyists. Also, a side effect of antibiotics is weight gain in livestock - so even legislation that ostensibly outlaws use for the direct purpose of directly adding to profits, language in regulation is generally kept for medical purposes of "reducing disease" among herds. Disease that is at a high rate because of high density feedlot practices...
There have been quantitative calculations for antibiotics taught for years in ag departments, and known among industry practitioners. Farming is a highly quantitative industry, and any agent of growth promotion is tracked carefully along with feed energy & cost inputs. Today you may have to go back to older documents to see talk about it in a more open manner though.
Here's a more industrial type of analysis paper (2003)
I think a weight loss factor could be added to legal antibiotics to remove the benefits of their overuse.. Caffeinated cows on a rampage might correct the industry.
