Effects of restricted versus conventional dietary adaptation on feedlot performance, carcass characteristics, site and extent of digestion, digesta kinetics, and ruminal metabolism 1,2 W. T. Choat*, C. R. Krehbiel* 3 , M. S. Brown†, G. C. Duff‡ 4 , D. A. Walker‡, and D. R. Gill* *Department of Animal Science, Oklahoma State University, Stillwater 74078; †Division of Agriculture, West Texas A&M University, Canyon 79016; ‡Clayton Livestock Research Center, Clayton, NM 88415 ABSTRACT: Three experiments were conducted to determine effects of restricting intake of the final fin- ishing diet as a means of dietary adaptation compared with diets increasing in grain over a period of 20 to 22 d on overall cattle performance, carcass characteristics, digestibility, digesta kinetics, and ruminal metabolism. In Exp. 1, 84 Angus × Hereford yearling steers (initial BW = 418 ± 29.0 kg) were fed for 70 d. Restricting intake during adaptation had no effect (P > 0.10) on overall ADG:DMI, but decreased (P < 0.05) DMI compared with ad libitum access to adaptation diets, which resulted from differences during the initial 28 d of the experi- ment. In Exp. 2, 150 mixed crossbred steer calves (ini- tial BW = 289 ± 22.9 kg) were fed for an average of 173 d. Restricting intake decreased (P < 0.01) overall daily gain (1.51 vs 1.65 kg/d) and DMI (8.68 vs 9.15 kg/d) compared with ad libitum fed steers; however, ADG:DMI was not influenced (P > 0.10) by adaptation method. Experiment three used eight ruminally and duodenally fistulated steers (initial BW = 336 ± 20 kg) in a completely random design. Total tract digestibility, Key Words: Adaptation, Beef Cattle, Carcass Quality, Performance, Restricted Feeding 2002 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2002. 80:2726–2739 1 Approved for publication by the Director of the Oklahoma Agric. Exp. Sta. This research was supported by the Oklahoma and New Mexico Agric. Exp. Sta. 2 The authors would like to acknowledge Lisa Blan, Kathryn Mal- colm-Callis, and Mathew Wiseman from the Clayton Livestock Re- search Center, Clayton, NM, Roy Ball and Bill Starr from the Willard Sparks Beef Research Center, Steve Welty from the Nutrition and Physiology Research Center, Tim Bodine, Carolyn Lunsford, Donna Perry, Christina Stout, and Joan Summers from the Ruminant Nutri- tion Laboratory, Stillwater, OK, and Ken Bolenbaugh of Bolenbaugh Farms, Carrier, OK for their contributions to these experiments. 3 Correspondence: 208 Anim. Sci. Bldg. (phone: 405/744-8857; fax: 405/744-7390; E-mail: kclinto@okstate.edu). 4 Present Address: Univ. of Arizona, Dept. of Anim. Sci., 217 Shanzt Bldg., Tucson, 85721. Received January 14, 2002. Accepted May 28, 2002. 2726 digesta kinetics and ruminal metabolism were deter- mined. Restricting intake reduced (P < 0.10) daily DMI variation from d 1 through 7, 8 through 14, and 22 through 28 compared with ad libitum feeding of three adaptation diets. Restricted steers had reduced (adap- tation method × period interaction, P < 0.05) intakes and fecal excretions of ADF and greater OM digestibili- ties on d 4 through 7, 11 through 14, and 18 through 21. Digesta kinetics and ruminal metabolism were gen- erally not affected (P > 0.10) by adaptation method. Our results suggest that restricted-feeding of the final diet as a means of dietary adaptation can be used in finish- ing cattle with few problems from acidosis or related intake variation. In light-weight steers (Exp. 2), disrup- tions in intake during the adaptation period might have resulted in restriction for an extended period, which decreased (P < 0.01) hot carcass weight compared with calves fed ad libitum. Effects of limit feeding during the initial 28 d of the feeding period on site and extent of digestion, digesta kinetics, and ruminal metabolism were minimal, supporting few differences in perfor- mance across the finishing period for yearling cattle. Introduction Traditionally, adapting cattle to high-grain diets has been accomplished by using sequential diets with an increasing grain concentration. This is done so that ruminal microorganisms can gradually adjust to a ru- minal environment with a lower pH in an attempt to minimize subacute acidosis and intake variation that can occur with overeating of grain. Restricting feed in- take of high-concentrate diets has improved feed effi- ciency in programmed feeding studies (Zinn, 1986; Loerch, 1990; Knoblich et al., 1997), in studies where cattle were restricted on a percentage of ad libitum (Plegge, 1986; Hicks et al., 1990) and in studies where cattle were fed to some maximum level relative to their maintenance energy requirements (Xiong et al., 1991; Bartle and Preston, 1992). Restricting intake of high-