View Full Table | Close Full ViewTable 1.

Composition (DM basis) of diets used in Exp. 1 (negative control without urea added [CON], positive control with conventional urea [UREA], and dietary treatments containing 1 of 2 slow-release urea sources: Optigen II1 [OPTI] or NitroShure2 [NITRO]) and Exp. 2 (CON)

 
Treatment
Item CON UREA OPTI NITRO
Dry-rolled corn, % 37.90 37.30 37.23 37.23
Corn earlage,3 % 30.00 30.00 30.00 30.00
Modified DG w/solubles, % 20.00 20.00 20.00 20.00
Corn silage, % 7.80 7.80 7.80 7.80
Urea, % 0.60
Optigen II, % 0.67
NitroShure, % 0.67
Dry supplement,4 % 4.30 4.30 4.30 4.30
Analyzed chemical composition,5 %
OM 93.6 93.5 93.6 93.6
CP 13.0 14.7 14.7 14.7
NDF 20.8 19.7 20.3 20.8
Starch 45.4 44.7 43.9 44.5
Calculated chemical composition, %
TDN, % 79.1 79.6 79.2 79.5
NEg, Mcal/kg 1.28 1.31 1.30 1.31
Basal DIP,6 % 6.6 6.6 6.6 6.6
Supplemental DIP,6 % 0.0 1.7 1.7 1.7
Total DIP,6 % 6.6 8.3 8.3 8.3
eNDF,6 % 6.6 6.6 6.6 6.6
1Contained 89% urea; Alltech Inc., Nicholasville, KY.
2Contained 89% urea; Balchem, New Hampton, NY.
3Ensiled corn ear: 8.2% CP, 22.4% NDF, and 1.30 Mcal/kg of NEg (DM basis), and 65.7% DM.
4Beef distillers finisher R-800 (Form-A-Feed Inc., Stewart, MN). Contained 800 g/ton of monensin (Rumensin90, Elanco Animal Health, Greenfield, IN), 7% salt, 25% Ca, 3% K, 10 ppm Co, 350 ppm Cu, 9 ppm Se, 1,750 ppm Zn, 148,000 IU/kg of vitamin A, 29,000 IU/kg vitamin D3, 165 IU/kg vitamin E, and 495 mg/kg of thiamine.
5Performed in duplicate on a composite derived from 8 samples.
6Based on published degradable intake protein (DIP) and effective NDF (eNDF) concentrations for each ingredient (Lardy et al., 1998; NRC, 2000; Cao et al., 2009).



View Full Table | Close Full ViewTable 2.

Intake and apparent total tract digestibility in cattle fed finishing diets without urea added (negative control [CON]), or added at 0.6% of dietary DM, in the form of conventional urea (positive control [UREA]) or 1 of 2 slow-release urea sources (Optigen II1 [OPTI] or NitroShure2 [NITRO])

 
Treatment
Item CON UREA OPTI NITRO SEM P-value
n 4 4 4 4
Intake, kg/d
DM 14.4 15.4 15.4 14.4 0.7 0.53
OM 13.5 14.3 14.4 13.5 0.7 0.58
Digestibility, %
OM 67.4 71.0 67.9 70.1 2.6 0.67
NDF 33.4 35.5 32.3 35.4 4.7 0.94
CP 63.1 70.0 66.7 70.8 2.5 0.21
CP3 63.1 66.4 62.4 67.3 2.6 0.51
Starch 87.7 88.3 87.3 89.5 2.0 0.56
1Contained 89% urea; Alltech Inc., Nicholasville, KY.
2Contained 89% urea; Balchem, New Hampton, NY.
3Estimated based on non-urea N intake.



View Full Table | Close Full ViewTable 3.

Total VFA ruminal concentration, VFA molar proportions, acetate-to-propionate ratio, ruminal pH, and urinary purine derivatives-to-creatinine (PDC) index at different times after feed delivery in cattle fed finishing diets without urea added (negative control [CON]), or added at 0.6% of dietary DM, in the form of conventional urea (positive control [UREA]) or 1 of 2 slow-release urea sources (Optigen II1 [OPTI] or NitroShure2 [NITRO])

 
Treatment
P-value
Item CON UREA OPTI NITRO SEM Treatment Time Treatment × time
n 4 4 4 4
pH 5.77 5.83 5.77 5.75 0.08 0.91 < 0.01 0.74
VFA, mM
Total 108.3 105.4 108.7 107.8 12.4 0.99 < 0.01 0.62
Branched-chain3 3.39 3.19 2.30 2.89 0.41 0.31 0.43 0.85
Acetate-to-Propionate 1.50a, x 1.36ab, x 1.08b, y 1.42ab, x 0.16 0.09 < 0.01 0.80
VFA, mol/100 mol
Acetate 49.0 47.6 45.7 48.6 1.1 0.18 < 0.01 0.59
Propionate 34.5b 35.8b 42.6a 37.2ab 2.4 0.07 < 0.01 0.99
Butyrate 11.7 11.8 7.5 9.5 2.2 0.40 0.17 0.43
PDC index4 161.1 168.5 171.4 175.0 10.6 0.63 < 0.01 0.91
1Contained 89% urea; Alltech Inc., Nicholasville, KY.
2Contained 89% urea; Balchem, New Hampton, NY.
3Summation of isobutyric, isovaleric, and 2-methyl butyric acids.
4 ; urinary concentrations (mM) of purine derivatives (PD) and creatinine (Crt); BW expressed in kg (Chen et al., 2004). Differences in PDC index among treatments indicated differences in microbial CP synthesis (Chen and Ørskov, 2004).
a,bMeans with uncommon superscripts differ (P < 0.05).
x,yMeans with uncommon superscripts differ (P < 0.10).



View Full Table | Close Full ViewTable 4.

Estimated degradable intake protein (DIP) supply, requirements, and balance (supply − requirements), and MP balance for cattle fed finishing diets without urea added (negative control [CON]), or added at 0.6% of dietary DM, in the form of conventional urea (positive control [UREA]) or 1 of 2 slow-release urea sources (Optigen II1 [OPTI] or NitroShure2 [NITRO])

 
Treatment
Item CON UREA OPTI NITRO
g/d
DIP supply3 983 1239 1239 1239
DIP requirements3 1023 1016 1015 1015
DIP balance3 −40 223 224 224
MP balance4,5 549 662 661 661
1Contained 89% urea; Alltech Inc., Nicholasville, KY.
2Contained 89% urea; Balchem, New Hampton, NY.
3Estimated using Level 1 of NRC (2000) model, which assumes that, when present, DIP deficiencies (DIP requirements > DIP supply) are overcome by degradable N supplementation. Therefore, the amount of microbial protein synthesized in the rumen per day was represented by daily DIP requirements.
4Estimated using modifications to the Level 1 of the NRC (2000) model: DIP balance = DIP supply – DIP requirements × 1.18; when DIP balance resulted positive, contribution of MCP to MP supply was calculated as DIP requirements × 0.64; when negative, the contribution was estimated as DIP supply × 0.85 × 0.64 (NRC, 2001).
5Cattle ADG for MP calculations was estimated using NRC (2000) equations and observed DMI and DM digestibility.