Submitted to: North Carolina Institution of Nutrition Research Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 4/20/2000
Publication Date: N/A
Technical Abstract: Forage species and fertilization level were evaluated in eight Angus growing steers (initial weight 217+ 15kg, final weight 252+ 9kg). In a replicated 4x4 latin square design, steers were fed four hays, dried with forced air, from two warm season grasses, gamagrass (Tripsacum dactyloides, G) and switchgrass (Panicum virgatum, S), which were fertilized with either r56.2 (L)or 168.5 (H) kg of N per hectare. Diets were limit-fed to provide 0.5 kg gain per day. Following 21d of adjustment, nitrogen balance was measured from days 22 - 27 of each period. Blood was collected during the balance trial via jugular catheters and analyzed for plasma urea N (PUN). G differed from S (P<0.05) in daily dry matter intake (4273 vs. 4185 g), N intake (72 vs. 67 g), dry matter digestibility (60.95 vs. 63.59%), fecal N (30.59 vs. 28.33 g/d), urine N (20.19 vs. 19.58 g/d), urine urea N (10.54 vs. 8.03 g/d), and percent of urinary N present as urea N (53.51 vs. 39.99%). By design, daily N intake was greater (P<0.05) for L (63.07 g) that for H (76.00 g). L also differed from H in dry matter digestibility (61.27 vs. 63.27%), urine N (13.56 vs. 25.94 g/d), and N retained as percent of N digested (58.55 vs. 43.46%). After adjustment by covariance for differences in N intake, fecal N excretion tended (P<0.09) to be greater for G than S. Compared to S, G had greater PUN, N digestibility, and N digested as fertilization level increased (forage x fertilization interactions, P<0.05). While there were no main effects upon N retention, there was an interaction (P<0.05) between forage and fertilization level; as fertilization level increased, N retention increased from 19.48 to 23.48 g/d in G and decreased from 21.06 to 18.10 g/d in S. Summary, fertilization affected N metabolism of steers when fed G more than when fed S.