J. Anim Sci., doi: 10.2527/jas.2006-741
©Copyright, 2007, The American Society of Animal Science
Effects of dry matter intake restriction on diet digestion, energy partitioning, phosphorus retention, and ruminal fermentation by beef steers
J. H. Clark 1,
K. C. Olson 2*,
T. B. Schmidt 3,
M. L. Linville 1,
D. O. Alkire 1,
D. L. Meyer 1,
G. K. Rentfrow 4,
C. C. Carr 1,
E. P. Berg 5
1 Division of Animal Sciences, University of Missouri-Columbia 920 East Campus Drive, Columbia, MO 65201
2 Department of Animal Sciences and Industry, 139 Call Hall, Kansas State University, Manhattan, KS 66506
3 Department of Animal and Dairy Sciences, Mississippi State University, Mississippi State, MS 39762
4 Department of Animal and Food Sciences, University of Kentucky, Lexington, KY 40546
5 Department of Animal and Range Sciences, North Dakota State University, Fargo, ND 58105
* To whom correspondence should be addressed. E-mail: kcolson{at}ksu.edu.
 |
Abstract |
|---|
Two experiments were conducted to determine the effects of DMI restriction on diet digestion, ruminal fermentation, metabolizable energy intake, and phosphorus retention by beef steers. In Exp. 1, 12 Angus x steers (average initial BW = 450 ± 18 kg) were assigned randomly to 1 of 3 diets that were formulated to promote a 1.6 kg ADG at intake levels corresponding approximately to 100% (AL), 90% (IR90), or 80% (IR80) of ad libitum DMI. In Exp. 2, 12 crossbred steers (average initial BW = 445 ± 56 kg) fitted with ruminal cannulae were randomly assigned to 1 of 2 diets that were formulated to promote a 1.6 kg ADG at either AL or IR80. All diets delivered similar total NE, MP, Ca, and P per d. During both experiments, fecal DM output by IR80 was less (P 
0.03) than that of AL; IR90 was similar (P = 0.51) to AL during Exp.1. Digestion of DM by IR80 cattle was greater (P 0.03) than that of AL during both experiments; IR90 was similar (P = 0.31) to AL during Exp. 1. Metabolizable energy intake was similar (P 
0.20) among treatments during both experiments, whereas P retention was similar (P 0.46) among treatments during Exp. 1. Total VFA and the molar proportion of acetate of AL were greater (P 0.03) than that of IR80 during Exp. 2; however, IR80 had a greater (P = 0.03) molar proportion of propionate. Under the conditions of these studies, restricting DMI while holding NE, ruminally-degradable protein, and MP intakes constant decreased fecal DM output and changed ruminal fermentation patterns in finishing steers. Improvements in performance associated with programmed-feeding regimes of the type studied here do not appear to be related to changes in diet digestion or metabolizable energy intake.
Key Words:
beef steers, digestion, energy partitioning, intake restriction
