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Abstract
Yield and quality components of corn crop residues, diet composition, residue intake, protein requirements, and performance of growing cattle grazing cornstalks were investigated.
Irrigated cornstalks had more (P <.05) residue available, lower (P <.05) leaf:stem ratio and crude protein (CP) content of all plant parts, and higher (P <.05) neutral detergent fiber (NDF) than dryland cornstalks. Differences in in vitro dry matter digestibility (IVDMD) were not consistent across years. Variation in husk IVDMD, CP and NDF was observed among corn hybrids at advanced stages of maturity. As grazing progressed, IVDMD and CP of leaf/husk decreased (P <.05). Leaf/husk was the plant part utilized in greatest amounts, while stem was poorly utilized. Most of the residual grain disappeared within the first month of grazing.
Crude protein of diets selected by esophageally fistulated steers decreased to less than 7% within the first month of grazing. The IVDMD of the roughage fraction of the diet decreased (P <.05) with time of grazing, the decrease being more rapid (P <.05) as stocking rate increased. As grazing progressed diet starch content decreased (P <.05) and NDF increased (P <.05). Adult experienced steers selected a diet with more starch than growing calves without previous experience in cornstalk grazing.
Calves grazing dryland fields gained faster (P <.05) than those grazing irrigated fields. A response in daily gain was observed to protein levels higher than the National Research Council's recommendations. At low levels of protein supplementation daily gain was positively correlated (P <.05) with diet CP but not with IVDMD nor with residual grain or leaf/husk available per animal. At protein levels above that required for maximum gain, daily gain was positively correlated (P <.05) with residual grain and leaf/husk available per animal and with IVDMD at the end of the grazing season.
A mathematical model that integrates the effects of weather, residue, management, and animals was developed to simulate residue yield, intake, diet composition and animal production. Although further testing of the model is required and possibilities for future improvement exist, the model adequately predicts animal performance. At the present stage of development it may be used as an aid in research planning by identifying areas where knowledge is lacking. Future uses of the model include optimization and management.
