Figure out who complained. That's your first thing to do. Find out what the problem is. Crowing? Smells? Flies? Or are they just being a tool? Talk to them if possible and figure out if a compromise can be reached.
If the problem is the later, there's not much you can do about it. Fight the laws, try to get legal, etc. do whatever you can, and if they insist on having an attitude, you can fight dirty right back at them --- but it should be a last resort because nobody really likes waging war with the neighbors.
If the problem is the later, there's not much you can do about it. Fight the laws, try to get legal, etc. do whatever you can, and if they insist on having an attitude, you can fight dirty right back at them --- but it should be a last resort because nobody really likes waging war with the neighbors.