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Performance of Steers Fed Crop Residues Supplemented with Nonprotein Nitrogen, Minerals, Protein and Monensin

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

Abstract

Research was conducted to test nonprotein nitrogen (NPN)-protein supplements in a mineral mixture for growing steers fed crop residues free choice. Three trials involving 184 steers were conducted. Animal performance and ruminal parameters were measured. Results indicate:

1. Supplements containing 7.5% sodium chloride, 10% dicalcium phosphate, 2.5% potassium carbonate, 2% magnesium sulfate, 1% elemental sulfur plus trace minerals, molasses and corn meal were readily consumed when combined with nitrogen sources to formulate 100% crude protein equivalent (CPE) mixtures.
   
2. Cottonseed hulls were readily consumed (3.1% of body weight [BW] per day), but chopped straw (2.0% BW) and corn stover (1.4% BW) were very poorly consumed.
   
3. Increasing nitrogen intake by the steers markedly increased cottonseed hull intake. Type of supplement and cottonseed hull intake (percent BW) were as follows: (a) negative control (no supplemental nitrogen source), 2.2%; (b) restricted 50% crude protein soybean meal control, 2.7%; and (c) 100% CPE supplements fed free choice, 3.1%.
   
4. Growing steers gained an average of .54 kg daily during 140-day trials when fed cottonseed hulls free choice plus either biuret or urea 100% CPE supplements. Replacing 20% of the NPN nitrogen with fish meal or soybean meal nitrogen increased gains by 20%. Treating the soybean meal protein with .6% formaldehyde did not improve steer performance.
   
5. Ruminal ammonia concentrations averaged 10 to 20 mg NH₃-N/100 ml of ruminal fluid for steers fed the 100% CPE supplements. Monensin addition to the supplement resulted in a 1.9 acetate/propionate ratio compared to a 5.0 ratio for control steers but reduced supplement and cottonseed hull intake and steer performance.
   

¹ Ruminant Nutrition Laboratory, Nutrition Institute, BeltsvUle, MD 20705.