It's an antimicrobial agent often used to control salmonella in poultry. Depending on the dose, it can be bacteriostatic (control the growth of bacteria) or bacteriocidal (kill the germs).
I looked for articles on the toxicity but didn't find any right away. There are plenty of articles about how it may trigger resistance in other infections like campylobacter (I've had that; it's not fun) and of course the impact on environment. But didn't turn up anything specific on toxicity in poultry.
Like any medication, if the dose is incorrect, you'll have a bad result. Have you checked with your local Dept. of Agriculture office? They may have answers.