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Plasma and Rumen Fluid Components of Steers Fed Two Sources and Levels of Nitrogen¹

University of Kentucky, ⁴ Lexington 40506

Abstract

Sixty-four yearling steers were used in a completely randomized design to study the effects of corn silage diets supplemented with soybean meal, urea, soybean meal-low-nitrogen and urea-low-nitrogen on growth and plasma and rumen fluid components. The diets were calculated to contain approximately 100% and 85% of the N.R.C. requirements for crude protein. The feeding period was 160 days in length. The steers receiving soybean meal at a higher level gained faster (P<.05) than each of the other treatment groups. Plasma urea nitrogen concentrations were higher (P<.01) on day 23 and on day 125 for steers fed the higher levels of soybean meal and urea. Lysine concentration was higher (P<.05) in plasma of steers fed the soybean meal supplemented diets when compared with the urea supplemented diets on day 23. Plasma concentrations of several of the essential amino acids (valine, isoleucine, histidine, leucine and lysine) were higher (P<.01) during the finishing phase (day 125) than during the growing phase (day 23). Of the nonessential amino acids, glutamic acid and glycine were lower (P<.01) during the finishing phase than during the growing phase. Rumen ammonia nitrogen concentration was higher in steers fed the two higher nitrogen level diets. Propionic acid concentration in rumen fluid was highest in the steers fed soybean meal at the higher nitrogen level.

¹ The investigation reported in this paper (72-5-111) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with approval of the Director.

² Present address: Clemson University, Clemson, S. C.

³ Present address: Lord Fairfax Community College, Middletown, Va.

⁴ Department of Animal Sciences.