Growth and Plasma Amino Acids of Steers Fed Different Nitrogen Sources at Restricted Intake

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Abstract
Fifty-six Holstein steers averaging 240 kg were used in a completely randomized design to study the effects of different nitrogen sources on performance, plasma amino acids and plasma urea-nitrogen. The steers were limited to, 7.95 kg daily of a corn-cottonseed hull diet containing no supplemental nitrogen (control), or diets supplemented with either urea or soybean meal (SBM) in a 112-day trial. Average daily gains were lower (P < .01) for the steers fed no supplemental nitrogen than for those fed diets supplemented with urea or SBM (.75 vs 1.15 and 1.13 kg, respectively). On day 28, plasma glycine and histidine were higher (P < .01) for the control group; arginine was lower (P < .05) for the control than SBM; lysine was lower (P < .01) for steers fed the urea supplemented diet than those fed the SBM supplemented diet. On day 56, glycine and histidine were higher (P < .05) for the control; isoleucine was higher (P < .05) for SBM than urea or the control; arginine was higher (P < .01) for SBM than the control. Plasma urea-nitrogen levels were lower (P < .01) for the control than SBM, and SBM was lower (P < .01) than urea at each sampling interval. Performance was observed to be very similar for SBM and urea-fed steers under the imposed conditions of this trial. Copyright © 1975. American Society of Animal Science . Copyright 1975 by American Society of Animal Science.

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