Effects of grazing allowance and system on the use of corn-crop residues by gestating beef cows.

Duplicate fields of corn-crop residues were grazed by 3- to 11-yr-old Charolais x Angus and Charolais x Angus x Simmental cows (average BW = 630 kg) in midgestation at allowances of .41, .82, and 1.64 ha/cow in a continuous-stocking system for 56 d in 1988 (yr 1) and 1989 (yr 2) and for 51 d in 1990 (yr 3), or at .41 ha/cow in a strip-stocking system for 56 and 51 d in yr 2 and 3, respectively. Body weight gains by cows grazing continuously stocked fields at .41, .82, and 1.64 ha/cow were -.06, -.01, and .41 kg/d (P = .02), respectively. Body weight changes by cows grazing continuously stocked and strip-stocked fields at .41 ha/cow were .15 and .30 kg/d in yr 2 and -.33 and -.53 kg/d in yr 3 (system x year, P = .08), respectively. Percentages of in vitro OM disappearance (IVOMD) of crop residues selected by ruminally fistulated steers (P = .22) and cow crop residue DMI (% of BW; P = .03) were 52.5, 1.64; 60.1, 2.87; and 61.7, 2.97 in fields continuously stocked at .41, .82, and 1.64 ha/cow after 21 to 35 d of grazing in yr 2 and 3, respectively. Selected crop residue IVOMD (P = .04) and crop residue DMI (percentage of BW, P = .07) were 58.0 and 2.46, respectively, in fields strip-stocked at .41 ha/cow. Mean yields of OM (P < .01) and IVOMD (P < .01) were 4,605, 2,136; 5,347, 2,495; and 5,761, 2,688 kg/ha in fields continuously stocked at .41, .82, and 1.64 ha/cow, respectively. Results imply that cows grazing corn-crop residues in continuously stocked fields are less likely to gain BW at grazing allowances < 1.64 ha/cow for 56 d. Differences in BW gains between cows grazing strip-stocked and continuously stocked crop residue fields were weather-dependent.