Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

L. D. Bunting


Initially, various solvents were tested for their efficacy in isolating soluble nitrogen (SN) from annual ryegrass and berseem clover. Plant nitrogen (PN) solubilities were similar in.5 M NaCl, autoclaved rumen fluid, borate phosphate buffer and Burroughs' solution. The mean PN solubilities across forages ranged from 12% for.1 M acetic acid to 45% for.2% NaOH. At 4$\sp\circ$C, 15% TCA precipitated the most soluble plant protein nitrogen (SPPN). Nitrogen (N) yield, concentrations of PN, SN, SPPN and soluble nonprotein nitrogen (SNPN) increased linearly as N fertilization (NF) increased from 0 to 335 kg N/ha. Decreasing defoliation interval (DI) from 6- to 2-wk decreased PN yield, and linearly increased concentrations PN, SN, SPPN and SNPN. However, NF and DI did not affect the proportions of SN, SPPN and SNPN in PN pools and the ruminal degradabilities of PN and dry matter (DM) as measured in nylon bags. Solubilities of PN and ruminal degradabilities of PN and DM declined with advancing growing season. A lamb metabolism study was conducted to determine the ruminal degradability and metabolic usage of ryegrass N as affected by NF (0 or 224 kg N/ha) and DI (2- or 6-wk). Abomasal flows of total N and NH$\sb3$ N were higher and abomasal flow of ADF$\sb-$N was lower in growing lambs fed fertilized vs unfertilized ryegrass. Similarly, abomasal flows of total N and NH$\sb3$ N were higher in the lambs fed 2-wk vs 6-wk regrowth ryegrass. Abomasal flow of microbial N was not affected by treatments. However, abomasal non-microbial N flow tended to be higher in lambs fed fertilized vs unfertilized or 2-wk vs 6-wk regrowth ryegrass. Ruminal and total tract digestibilities of DM, and NDF and ADF were higher for fertilized than for unfertilized ryegrass. When compared to lambs fed unfertilized ryegrass, those fed fertilized ryegrass had higher BUN (21.4 vs 13.3 mg/dl) and rumen NH$\sb3$ N (21.4 vs 13.4 mg/dl), and tended to have higher ruminal free amino acids and pH, and retained more N. Lambs fed 2-wk DI ryegrass tended to retain more N than those fed 6-wk DI ryegrass.