Utilization of Low-Quality Native Grass Hay by Beef Cows Fed Increasing Quantities of Corn Grain

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Abstract
Four supplements providing 0, 1, 2 or 3 kg/d of ground corn were fed to beef cows maintained on low-quality native grass hay to determine the effect of corn supplementation on forage utilization and intake. Cottonseed meal was blended with the corn to equalize supplemental protein intake (256 g/d). Twelve Hereford cows (average weight, 395 kg) and four mature, ruminally cannulated Hereford × Angus heifers (average weight, 328 kg) were individually penned and offered coarsely chopped (5-cm screen) native grass hay that had been harvested in November (4.2% crude protein, 52.5% acid detergent fiber). Digestibility of hemicellulose and cellulose decreased linearly (P<.0001) as the amount of supplemental corn increased. A cubic response (P<.05) was observed for hay organic matter (OM) digestibility (36.5, 35.1, 23.6 and 18.9% for 0 through 3 kg corn, respectively). Hay intake decreased linearly (P<.0001) with increased corn supplementation (8.7 to 5.1 kg/d). A cubic response (P<.005) for digestible OM intake (3.4, 3.8, 3.2 and 3.3 kg/d) suggested improved energy intake when 1 kg of corn was fed. Digestible OM intake of cattle fed 2 or 3 kg corn/d, however, was not significantly greater than the control. Particulate passage rate decreased linearly (P<.05) from 3.90 to 3.68%/h with increased supplemental corn. Ruminal NH3-N concentrations decreased linearly (P<.05) as supplemental corn increased and remained below 1 mg/dl throughout the day when 3 kg corn/d was fed, indicating a ruminal degradable protein deficiency. This study suggests that feeding 2 or 3 kg of grain-based supplements formulated only to meet the total protein requirement of mature beef cows may decrease forage utilization to the extent that overall energy status of the cow is not improved. Copyright © 1987. American Society of Animal Science . Copyright 1987 by American Society of Animal Science