The millionaire casino executive and former beauty queen recently suggested that people barter with doctors for medical care, like when "our grandparents would bring a chicken to the doctor."
Democrats responded by setting up a website, "Chickens for Checkups," and by sending volunteers in chicken suits to her campaign events.
Lowden is in a 12-way primary race to decide Senate Majority Leader Harry Reid's Republican opponent. She had been the front-runner in the race, but was in a virtual tie for the lead in a recent poll.
Under the new rule, chicken costumes will be banned along with political buttons, shirts, hats and signs within 100 feet of polling places.
Washoe County Registrar of Voters Dan Burk said such a costume would be an "inappropriate and obvious" advocacy message against Lowden.
Lowden campaign manager Robert Uithoven hailed the decision.
"I think voters will be spared the Harry Reid carnival and that's a good thing," he told The Associated Press. "I think most voters are going to the polls thinking about far greater things than Harry Reid's chickens."
Reid spokesman Jon Summers said the Nevada Democratic Party has been sending the volunteers in chicken costumes to Lowden events and he was unaware of any plans for them to show up at the polls.
"Maintaining fair elections is an important thing and we respect the decision that has been made by election officials," he said. "I certainly can understand why that would be a sensitive issue for her since she has been called out on her concept of bartering chickens for checkups."
Early voting began Saturday in the June 8 primary.