It does look like it is in the Lamiaceae family, which includes the genera for sages, salvias, and mints. They all have square stems, and that is probably why tinyscrafts was asking.
I don't think it will harm your chickens, and I doubt they will eat it (much.) The worst I can think of that plants in that family do are cause skin irritation in allergic individuals, some are edible, some others-animals don't usually eat, like sage.
I am curious what its name is, as well a closer pic. I haven't seen anything exactly like that around here.