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Diet Composition and Daily Gain of Growing Cattle Grazing Dryland and Irrigated Cornstalks at Several Stocking Rates¹

University of Nebraska, Lincoln 68583

Abstract

Diet composition and the relationships between daily gain of calves grazing cornstalks and certain characteristics of the available residue and diets selected by esophageally fistulated cattle were studied in two trials during November and December of 1984 (Trial 1) and of 1986 (Trial 2). Eight adult steers and four esophageally fistulated calves were used in Trials 1 and 2, respectively, to collect extrusa samples from dryland and irrigated fields grazed at several stocking rates. Steers grazing irrigated cornstalks selected a diet with more (P < .05) starch and less (P < .05) CP than those grazing dryland fields. As grazing continued, extrusa starch content decreased (P < .05). In vitro DM disappearance (IVDMD) of both diet and the roughage fraction of the diet decreased (P < .05) with days of grazing; this decrease was greater (P < .05) at higher stocking rates. Calves grazing dryland fields gained faster (P < .05) than calves grazing irrigated fields. With a low level of protein supplementation (213 g CP/d, Trial 1), daily gain was positively correlated with CP of both diet (extrusa) or available leaf plus husk but not with grain available per animal or with extrusa IVDMD, suggesting that protein was first limiting. With a higher level of protein supplementation (458 g CP/d, Trial 2), daily gain was correlated positively with residue available per animal and IVDMD of extrusa at the end of the grazing season. The energy value of feed consumed by cattle grazing cornstalks decreases with time, and complex interactions between protein needs and energy intake may occur.

¹ Published with the approval of the Director as Paper No. 8544, Journal Ser., Nebraska Agric. Exp. Sta.

² Present address: Universidad Autonoma Chapingo, Departamento de Zootecnia, Chapingo, Mexico 56230.

³ Dept. of Anim. Sci.