Jun 20, 2019 · Starter feeds used from zero to three weeks we use a 1/8-inch screen, the finest grind that we do,” Cindy says. “Then for growers we’ll mix 50 percent of this fine grind [1/8-inch screen] and 50 percent medium grind with a ¾-inch screen. This starts at around two to three weeks and continues until the birds are five weeks.