Wheat Straw-Urea Diets for Beef Steers: Alkali Treatment and Supplementation with Protein, Monensin and a Feed Intake Stimulant

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Abstract
Diets of wheat straw, urea and minerals were fed to growing steers in two 105-day feeding trials and to rumen-fistulated steers in two short-term changeover trials to evaluate the effects of alkali treatment, fine grinding and pelleting, and supplementation with small amounts of protein, a chemical feed intake stimulant (elfazepam5) and monensin5. In experiment 1, alkali (A) treatment (4 kg NaOH/100 kg straw) increased apparent organic matter digestibility in coarsely ground straw (C) (54 vs 69%, P<.01) but not in finely ground pefleted straw (P) (56 vs 62%, P>.05). On straw supplemented with urea and minerals, intake and weight gain of growing steers ranged from 1.6% of body weight and .09 kg/day for C straw to 2.5% of body weight and .61 kg/day for AP straw. In samples taken 3 hr after feeding, rumen ammonia levels were lower (31.4 vs 20.9 mg N/100 ml, P<.01), and total VFA levels were higher (27.4 vs 46.1 mM/liter, P<.01) in steers fed the A treatment compared to those fed the control diet. Plasma total amino acids were higher (P<.05) with A or P treatments, but the proportion of essential amino acids did not differ between treatments. Replacing 10% of supplemental urea-N with soybean meal-N had no effect on intake, gain and rumen or blood parameters. In fistulated steers, weight and volume of total rumen ingesta did not vary (P>.01) between diets; however, the rumen retention time of undigested particles was reduced from 44 to 35 hr (P<.01) by P treatment of straw and to 25 hr (P<.01) by A treatment. In experiment 2, diets of P or AP straw plus urea and minerals were supplemented with monensin (30 ppm of the diet), alfazepam (10 mg/head/day) or both. In fistulated steers fed AP diets, neither chemical affected the weight or volume of rumen ingesta, rumen retention time or rumen pH, ammonia or total volatile fatty acids; however, monensin reduced (P<.01) the acetate to propionate ratio from 5.1 to 3.4. In growing steers, monensin reduced (P<.05) intake from 2.0 to 1.5% BW and weight gain from .37 to .05 kg/day in P diets and from 2.6 to 2.1% BW and .76 to .61 kg/day in AP diets. Elfazepam had no effect on intake or weight gain. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.