Nick Grigg, Alex Allan and Mike Dewar start for County with Cameron Fenton on the bench.
Junior Bulumakau has been named on the wing for Ayr who take on Gala at Millbrae on Saturday.
George Hunter, Javan Sebastian, Will Bordill and D'arcy Rae also feature for the Premiership leaders.
On loan Warriors George Horne and Robbie Fergusson start for London Scottish in tonight's Championship meeting with Bristol at Ashton Gate.