Restricted versus step-up dietary adaptation in Nellore bulls: Effects over periods of 9 and 14 days on feedlot performance, feeding behavior and rumen morphometrics

•Cell proliferation after 9 days of adaptation shows that papillae are still growing.•Adaptation for 14 days is adequate for the proper development of rumen epithelium.•Nellore bulls had greater fiber digestibility for 14 days versus 9 days of adaptation.•Nellore cattle should be adapted for 14 days regardless of the protocol.