EFFECTS OF GRAZING ALLOWANCE AND SYSTEM ON THE USE OF CORN-CROP RESIDUES BY GESTATING BEEF-COWS

Duplicate fields of com-crop residues were grazed by 3- to 11-yr-old C harolais 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) a nd for 51 d in 1990 (yr 3), or at .41 ha/cow in a strip-stocking syste m for 56 and 51 d in yr 2 and 3, respectively. Body weight gains by co ws grazing continuously stocked fields at .41, .82, and 1.64 ha/cow we re -.06, -.01, and .41 kg/d (P = .02), respectively. Body weight chang es by cows grazing continuously stocked and strip-stocked fields at .4 1 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 dis appearance (IVOMD) of crop residues selected by ruminally fistulated s teers (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 .4 1, .82, and 1.64 ha/cow after 21 to 35 d of grazing in yr 2 and 3, res pectively. Selected crop residue IVOMD (P = .04) and crop residue DMI (percentage of BW, P = .07) were 58.0 and 2.46, respectively, in field s strip-stocked at .41 ha/cow. Mean yields of OM (P < .01) and IVOMD ( P < . 0 1) 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 s tocked 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-st ocked and continuously stocked crop residue fields were weather-depend ent.