title: Effects of dry matter intake restriction on diet digestion, energy partitioning, phosphorus retention, and ruminal fermentation by beef steers.
abstract: Two experiments were conducted to determine the effects of DMI restriction on diet digestion, ruminal fermentation, ME intake, and P retention by beef steers. In Exp. 1, twelve 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% (ad libitum, AL), 90% (IR90), or 80% (IR80) of ad libitum DMI. In Exp. 2, twelve 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 AL or IR80. All diets delivered similar total NE, MP, Ca, and P per day. 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 regimens of the type studied here do not appear to be related to changes in diet digestion or ME intake.
authors.affiliation: Division of Animal Sciences, University of Missouri-Columbia 920 East Campus Drive, Columbia, MO 65201, USA.
authors.forename: J H
authors.initials: JH
authors.lastname: Clark
authors.forename: K C
authors.initials: KC
authors.lastname: Olson
authors.forename: T B
authors.initials: TB
authors.lastname: Schmidt
authors.forename: M L
authors.initials: ML
authors.lastname: Linville
authors.forename: D O
authors.initials: DO
authors.lastname: Alkire
authors.forename: D L
authors.initials: DL
authors.lastname: Meyer
authors.forename: G K
authors.initials: GK
authors.lastname: Rentfrow
authors.forename: C C
authors.initials: CC
authors.lastname: Carr
authors.forename: E P
authors.initials: EP
authors.lastname: Berg
mesh_terms: D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000254:growth & development* / Q000378:metabolism*; D004063:Digestion; D002149:Energy Intake / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology; D005232:Fatty Acids, Volatile / Q000032:analysis / Q000378:metabolism; D005285:Fermentation; D008297:Male; D010758:Phosphorus / Q000378:metabolism*; D011897:Random Allocation; D012417:Rumen / Q000378:metabolism* / Q000382:microbiology; D015430:Weight Gain