J. Anim Sci.
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J. Anim Sci. 1978. 47:927-934.
© 1978 American Society of Animal Science
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Plasma Urea Nitrogen Levels in Beef Steers Grazing Nitrogen-Fertilized Bermudagrass and Orchardgrass-Ladino Pastures1

L. A. Carver2 ,3,, K. M. Barth2, J. B. McLaren2, H. A. Fribourg4, J. T. Connell4,5, and J. M. Bryan5

University of Tennessee, Knoxville 37901

Abstract

Blood samples were collected by jugular puncture, initially and at four times during one grazing season, from steers grazing Midland bermudagrass pastures (1) not fertilized with nitrogen (N), or fertilized in three equal installments with either (2) 112, (3) 224, or (4) 448 kg N/ha/year or grazing (5) common bermudagrass (112 kg N/ha/year) and (6) orchardgrass-ladino clover pastures. The blood plasma was analyzed for urea nitrogen (PUN). Each increment in N fertilization of Midland resulted in an increase in PUN levels of steers grazing these pastures. The data were reduced to polynomials describing the regression of crude protein (CP) and in vitro digestible dry matter (IVDDM) content of consumed forage and average daily gain (ADG) on PUN. PUN levels estimated from a regression equation which are necessary to sustain gains of .5 kg/day were 15, 10, 15, 25, 15 and 8 mg/100 ml for treatments 1 through 6, respectively. Animals grazing all pastures consumed enough CP to attain or exceed these levels at the beginning of the grazing season. However, PUN levels of the steers grazing the bermudagrass treatments fell below these levels 48, 75, 75, 48 and 48 days after the beginning of the grazing season, respectively. Animals grazing orchardgrass-ladino maintained a high enough PUN level throughout the grazing season to sustain an ADG of .5 kg/head/day.

Footnotes

1 Published with the permission of the Dean of the University of Tennessee Agricultural Experiment Station.

2 Department of Animal Science.

3 Present Address: NU-Labs Division, Pioneer Hi-Bred International, Inc., Johnston, Iowa 50131.

4 Department of Plant and Soil Science.

5 Ames Plantation, Grand Junction, TN.






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Copyright © 1978 by the American Society of Animal Science.