one worth trying is diluted apple/cider vinegar or even normal vinegar,it acts as a detterent to ants and sends them back the way they came from,have just had a check on toxicity to chickens and it seems to be recommended in fact as it kills bacteria in coops apparently,woud recommend everyone does there own research into it to of course.
this is really only suitable for coops on hard ground like concrete but the vinegar solution needs mopping/spreading on the ground-inside and on the outside of the coop,not so its swimming in it but so its evenly mopped all over...it stinks badly [if are not one for vinegar!] but it honestly does work,well it does on UK ants.
though have not tried it with chickens before,we get plagued with ants in our home every summer,had found out about vinegar on the internet and gave it a try-immediately it had sent the ants into retreat,not one ant to be seen again until the solution dried up.