This is a classic misuse of the word "need". Antibiotics increase growth rates, but is optional. Without antibiotics, the growth rate is reduced, but the drawbacks of antibiotics, some known, some unknown, are not present.
If antibiotics are not directly correlated here, Im wondering if they already tried to measure "sweet spot" of such treatment use (they are able to get the best effect of antibiotics paying as low as possible for them).
I'm also wondering about those numbers, they are clearly stable in 3 years row (using data from last 6 years) there might be some methodology that is applied between food companies, like mean 3 years average ?