Manipulation of nitrogen digestion by sheep using defaunation and various nitrogen supplementation regimens

Five ruminally, duodenally, and ileally cannulated sheep (average BW 62 kg) were fed 65% roughage:35% concentrate diets (CP = 15%) in a 5 X 5 Latin square design to study the applicability of using a combination of defaunation with N supplements (soybean meal [SBM], corn gluten meal [CGM], blood meal [BM], urea, and casein) with different extents of ruminal degradation to manipulate microbial protein synthesis and amount of ruminal escape protein. Diets were fed twice daily (1,759 g DM/d). Defaunation was accomplished with 30-ml doses of alkanate 3SL3 (active ingredient: sodium lauryl diethoxy sulfate)/sheep daily for 3 d with 2 d of fasting. Treatment 1 (control) involved feeding faunated sheep a diet in which the supplemental N (45% of total dietary N) was 67% SBM N and 33% urea N. Treatment 2 involved feeding defaunated sheep the same diet as the control. Treatments 3, 4, and 5 involved feeding defaunated sheep diets in which the supplemental N source was either 67% CGM-BM (1:1 N ratio) N:33% urea N, or 33% CGM-BM N:67% urea N or 33% CGM-BM N:33% urea N:33% casein N, respectively. Compared with the faunated control, defaunation decreased (P < .05) ruminal ammonia concentration (19 vs 26 mg/dl) and increased (P < .05) CP flow to the duodenum (253 vs 214 g/d) due to a trend for increases in both bacterial (BCP) and nonbacterial (NBCP) CP flows. Consequently, defaunation increased (P <.05) total amino acid (AA) flow to the duodenum (185 vs 155 g/d) and tended to increase (P < .13) the quantity of AA disappearing (124 vs 102 g/d) from the small intestine (SI). Replacement of SBM with CGM-BM with low or high levels of urea (Treatments 3 and 4) increased (P < .05) CP (305 or 292 vs 253 g/d) and total AA (235 or 215 vs 185 g/d) flows to the duodenum and increased (P < .05) the total AA disappearance (177 or 157 vs 124 g/d) from the SI. Adding casein to the diet instead of urea (Treatment 5 vs 4) failed to prove beneficial, indicating that defaunation did not limit the supply of free AA and peptides for ruminal bacterial growth or activity.