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

U. S. Department of Agriculture, Beltsville, MD 20705

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.

¹ Ruminant Nutrition Laboratory, Nutrition Institute, Agricultural Research, Science and Education Administration, Beltsville, MD 20705.

² Visiting scientist on sabbatical leave from: Division of Plant Industry, CSIRO, Canberra A.C.T. 2601, Australia.

³ Present address: U. S. Meat Animal Research Center, P. O. Box 166, Clay Center, NE 68933.

⁴ Authors wish to thank Mr. W. Woods for preparation of the diets, Mr. V. Beall and Mr. J. Grinsted for the feeding and care of the experimental animals, and Mr. B. Phillips, Mr. E. Williams and Mr. J. Humphrey for skilled technical assistance. The plasma amino acid analyses were carried out by Mr. W. Marcus.