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 compo sitions of stockpiled perennial forages and corn crop residues and com pare performance of cows grazing these forages or maintained in a dryl ot during winter. Midgestation, mature, medium-framed crossbred beef c ows (mean BW, 506 kg; mean condition score, 5.3) 1) strip-grazed repli cated fields containing stockpiled tall fescue-alfalfa, 2) strip-graze d stockpiled smooth bromegrass without (yr 1) and with (yr 2 and 3) re d clover, 3) strip-grazed corn crop residues at 1.2 cows/ha, or 4) the y were confined in a drylot for 129 to 141 d. All cows were offered gr ass-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 stockp iled perennial forages during the winter grazing seasons. Initial in v itro organic matter disappearance (IVOMD) and CP concentrations were g reater (P < .05) and initial NDF, ADF, and ADIN concentrations in stoc kpiled forages were lower (P < .01) than those in corn crop residues. Mean changes in IVOMD, CP, NDF, and ADF concentrations during the graz ing season were -.09, -.004, .10, and .11 percentage units OM/d, and t hey did not differ (P > .05) among forage species or grazed and nongra zed 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. Becau se cows grazed stockpiled tall fescue-alfalfa, smooth bromegrass-red c lover, and corn crop residues for 85, 83, and 57 d before beginning ha y supplementation, cows grazing these forages required 1,069, 1,031, a nd 627 kg/cow less hay DM to maintain body condition than cows confine d in a drylot.