Potential of stockpiled perennial forages in winter grazing systems for pregnant beef cows.

We conducted a 3-yr study to measure herbage masses and chemical compositions of stockpiled perennial forages and corn crop residues and compare performance of cows grazing these forages or maintained in a drylot during winter. Midgestation, mature, medium-framed crossbred beef cows (mean BW, 506 kg; mean condition score, 5.3) 1) strip-grazed replicated fields containing stockpiled tall fescue-alfalfa, 2) strip-grazed stockpiled smooth bromegrass without (yr 1) and with (yr 2 and 3) red clover, 3) strip-grazed corn crop residues at 1.2 cows/ha, or 4) they were confined in a drylot for 129 to 141 d. All cows were offered grass-legume hay as large round bales to maintain a condition score of 5 on a 9-point scale. Mean initial amounts (P < .05) and daily changes (P < .01) of OM mass were greater in corn crop residues than in stockpiled perennial forages during the winter grazing seasons. Initial in vitro organic matter disappearance (IVOMD) and CP concentrations were greater (P < .05) and initial NDF, ADF, and ADIN concentrations in stockpiled forages were lower (P < .01) than those in corn crop residues. Mean changes in IVOMD, CP, NDF, and ADF concentrations during the grazing season were -.09, -.004, .10, and .11 percentage units OM/d, and they did not differ (P > .05) among forage species or grazed and nongrazed areas. Cows grazing stockpiled tall fescue-alfalfa had greater (P < .05) BW gains than those in other systems and greater (P < .05) body condition score increases than cows grazing corn crop residues. Because cows grazed stockpiled tall fescue-alfalfa, smooth bromegrass-red clover, and corn crop residues for 85, 83, and 57 d before beginning hay supplementation, cows grazing these forages required 1,069, 1,031, and 627 kg/cow less hay DM to maintain body condition than cows confined in a drylot.