Effect of Urea at Different Nitrogen Levels on Digestibility and on Performance of Growing Steers Fed Low Quality Flood Meadow Roughage

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Abstract
Urea in amounts to provide one-half and all the nitrogen supplement in 6, 9 and 12% protein rations was compared with an all cottonseed meal supplement in a wintering ration for steer calves fed a low quality native meadow hay. Native meadow hay containing 5.5% crude protein or rations increased to 6% crude protein, regardless of supplement source, were not adequate to produce satisfactory gains of weaner steer calves. Body weight gains, feed intake and feed efficiency were significantly greater from the 9 and 12% protein diets than from the 6% diets or meadow hay alone. Urea used as the sole supplement to raise the crude-protein content of a low quality meadow hay roughage from 5.5 to 12% was highly toxic and caused fatalities in two animals from ammonia toxicity. The third animal on the treatment was removed from the experiment. Source of protein had no significant effect on feed intake, feed efficiency or gains when comparing all levels of protein. However, at the 9 and 12% protein levels source of protein had a significant effect on daily gains. The steers on the cottonseed meal supplement alone out-performed the steers on cottonseed meal and urea at both levels of protein. Level of nitrogen significantly affected digestibility of cellulose, dry matter and organic matter with the 9 and 12% crude-protein levels having higher values than the 6% level and hay alone, but they were not different from each other. Nitrogen digestibility significantly increased with each increase in nitrogen level of the diet, regardless of source of supplement. Source of nitrogen in the diet had no significant effect on digestibility of the nutrients studied. However, there was an interaction of source and level of nitrogen in the 6 and 9% diets on nitrogen digestibility. Nitrogen digestibility was lowest at the 6% level but highest at the 9% level when urea was the sole source of nitrogen supplementation.