I don't think so, without opening up the addon itself. I'm not sure where and how sound effects for addons are configured, but I'm assuming it's similar to the description.ext method. In other words, somewhere in a config someplace, there'll be an entry for the sound the chickens make -> this sound probably has a dB of far too much, since it's this number that determines how far the sound carries.
So, unless the farmlanders have added some code-switch that can turn off the chickens without resorting to opening the pbo and manually changing it...
Suggestion: script a workaround, where you spawn the chickens only when close enough. Or, since this is OFP, return them to life with a setdamage 0 whenever the player is close enough, and then kill them again ^_^
Wolfrug out.