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United States Department of Agriculture

Agricultural Research Service

Title: Intake Preference and Nitrogen Metabolism in Beef Steeers Grazing Bermudagrass, Caucasion Bluestem Or Gamagrass.

Authors
item Huntington, Gerald - NORTH CAROLINA STATE UNIV
item Burns, Joseph
item Archibeque, Shawn - NORTH CAROLINA STATE UNIV

Submitted to: North Carolina Institution of Nutrition Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: August 27, 2002
Publication Date: October 10, 2002
Citation: Huntington, G.B., Burns, J.C., Archibeque, S.L. 2002. Intake preference and nitrogen metabolism in beef steers grazing bermudagrass, caucasion bluestem or gamagrass.. North Carolina Institution of Nutrition Research Symposium.

Interpretive Summary: Our objective was to evaluate three warm-season grasses from the perspective of forage composition, selection by grazing beef steers, and nitrogen (N) metabolism in ruminants. Paddocks of bermudagrass (Cynodon dactylon, BG), caucasian bluestem (Bothriochloa caucasia, CBS), and gamagrass (Tripsacum dactyloides, GG) were fertilized with 70 lbs of N per acre about 60 and 30 days before sample collection. In 2000 and 2001, 12 steers (250 kg BW) were blocked on the basis of liveweight and then randomly assigned to a replicated, randomized complete block design with two paddocks of each forage and two steers per paddock. After at least 14 days adaptation, urine and blood samples were collected from each steer for determination of serum urea N (SUN, mM)and percentage of urinary N in the form of urea (PCTUREA). One steer per paddock was infused i.v. with 15,15 N-urea for 48 hours before urine was collected for six hours to measure enrichment of urea, urea entry rate (UER, mmol N/h), and urinary urea excretion (UUE, mmol N/h). Three other steers with esophageal fistulas were used to collect masticate samples that represent the steers' intake preferences. Forage composition data are for 2000 only. The CP (%of DM) and NPN (%DM) content were highest for BG canopy (12.0 and 3.1), followed by GG (9.0) and BG (8.9) canopy followed by CBS (7.3). However, crude protein was higher in masticate for GG (13.8) than BG (11.8) or CBS (9.8). Masticate from GG was higher in true protein (12.2) than masticate from BG (8.7)or CBS (8.1). Steers grazing CBS had lower (P<0.05) SUN, PCTUREA, and UER(2.49, 31.5, and 177) than steers grazing BG (12.23, 69.9, and 294) or GG (10.14, 66.3, and 266). The proportion or UER excreted as UUE was lower (P<0.10) for CBS (0.11) than for BG (0.54) or GG (0.35). Responses in SUN and PCTUREA, and UER reflect canopy or masticate for CBS and GG, but those two forages differed in SUN, PCTUREA, and UER. We conclude that compositional differences among the forage species affected proportions of nitrogen absorbed as non-protein N and affected urea production and recycling by the steers.

Technical Abstract: Our objective was to evaluate three warm-season grasses from the perspective of forage composition, selection by grazing beef steers, and nitrogen (N) metabolism in ruminants. Paddocks of bermudagrass (Cynodon dactylon, BG), caucasian bluestem (Bothriochloa caucasia, CBS), and gamagrass (Tripsacum dactyloides, GG) were fertilized with 70 lbs of N per acre about 60 and 30 days before sample collection. In 2000 and 2001, 12 steers (250 kg BW) were blocked on the basis of liveweight and then randomly assigned to a replicated, randomized complete block design with two paddocks of each forage and two steers per paddock. After at least 14 days adaptation, urine and blood samples were collected from each steer for determination of serum urea N (SUN, mM)and percentage of urinary N in the form of urea (PCTUREA). One steer per paddock was infused i.v. with 15,15 N-urea for 48 hours before urine was collected for six hours to measure enrichment of urea, urea entry rate (UER, mmol N/h), and urinary urea excretion (UUE, mmol N/h). Three other steers with esophageal fistulas were used to collect masticate samples that represent the steers' intake preferences. Forage composition data are for 2000 only. The CP (%of DM) and NPN (%DM) content were highest for BG canopy (12.0 and 3.1), followed by GG (9.0) and BG (8.9) canopy followed by CBS (7.3). However, crude protein was higher in masticate for GG (13.8) than BG (11.8) or CBS (9.8). Masticate from GG was higher in true protein (12.2) than masticate from BG (8.7)or CBS (8.1). Steers grazing CBS had lower (P<0.05) SUN, PCTUREA, and UER(2.49, 31.5, and 177) than steers grazing BG (12.23, 69.9, and 294) or GG (10.14, 66.3, and 266). The proportion or UER excreted as UUE was lower (P<0.10) for CBS (0.11) than for BG (0.54) or GG (0.35). Responses in SUN and PCTUREA, and UER reflect canopy or masticate for CBS and GG, but those two forages differed in SUN, PCTUREA, and UER. We conclude that compositional differences among the forage species affected proportions of nitrogen absorbed as non-protein N and affected urea production and recycling by the steers.

Last Modified: 9/23/2014
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