Escape protein supplementation for growing cattle grazing corn residues

Metabolizable protein may limit the growing pattern of calves, therefore four trials were conducted to assess the importance of escape protein (EP) supplementation for calves grazing corn residues. Growing calves grazed non-irrigated and irrigated corn residue fields during the 1987 and 1988 fall-winter periods. Cattle were maintained on different methods of feeding, levels and sources of EP supplementation. Animal performance, diet composition and availability and chemical characteristics of several corn residue fractions collected throughout the grazing season were evaluated. Animal daily gains were not affected by EP (P $\u3e$.05) during the first 14-21 d of grazing. A positive response (P $\u3c$.05) to EP supplementation was found the following 15 d. Residual grain was the highest quality plant part component and its daily rate of disappearance from the corn residue field was inversely related with the EP supplementation effect suggesting that corn provided enough metabolizable protein to meet the calf requirements. When two levels and qualities of alfalfa hay were used as sources of supplemental protein, calves still responded (P $\u3c$.05) to EP supplementation implying that alfalfa was limiting in metabolizable protein. Crude protein, EP, in vitro DM disappearance and grain content in extrusa samples, collected with esophageally-fistulated steers, decreased (P $\u3c$.05) in a linear and(or) quadratic manner as the grazing season progressed. Husk was the highest quality roughage fraction selected by the animals. Disappearance of the leaf blade fraction during the grazing period was associated with weathering damage as well as grazing effects. Stems, leaf sheaths and cobs were not usually selected; however, they may be consumed especially during high snow cover or during overgrazing conditions. Non-irrigated corn residue field parts had higher (P $\u3c$.05) CP, EP and in vitro DM disappearance than irrigated fields and as a consequence, non-irrigated promoted higher (p $\u3c$.05) animal gains than irrigated corn residue fields. Metabolizable protein needs of growing cattle were met when EP was provided. Metabolizable protein was not the first limiting nutrient during the first two weeks of the grazing season