Effects of encapsulated nitrate on growth performance, carcass characteristics, nitrate residues in tissues, and enteric methane emissions in feedlot beef steers: Finishing Phase.

A finishing feedlot study was conducted with beef steers to determine effects of encapsulated nitrate (EN) on growth performance, carcass characteristics, methane production, and nitrate (NO₃^-) residues in tissues. The 132 crossbred steers were backgrounded in a feedlot and transitioned to the high concentrate diets evaluated in the present study. The steers were initially assigned to 22 pens (6 animals per pen) in a randomized complete block design with BW (18 pens) and animals designated for methane measurement (4 pens) as blocking factors. Five animals in each pen designated for methane measurement were monitored for methane emissions in respiratory chambers twice during the finishing period. Pens received 3 dietary treatments (7 pens each): Control, a finishing diet supplemented with urea (0.03% NO₃^- and 0.9% urea in dietary DM); 1.25% EN, the control diet supplemented with 1.25% EN (1.1% NO₃^-) which partially replaced urea; 2.5% EN, the control diet supplemented with 2.5% EN (2.0% NO₃^-) fully replacing urea. The final pen designated only for methane measurement received a fourth dietary treatment, 2.3% UEN; control diet supplemented with unencapsulated NO₃^- (UEN; 2.0% NO₃^- in dietary DM) fully replacing urea. The cattle weighed 449 ± 32 kg at the start of the finishing period. The 2.5% EN diet decreased DMI (9.9 vs 10.7 and 10.7 kg/d; P < 0.01) compared with Control and 1.25% EN. Feeding EN tended to increase ADG (1.41 vs 1.36 kg/d; P = 0.09) and increased gain:feed (0.137 vs 0.127 kg/kg; P < 0.01) for EN compared with Control. No differences in methane production and yield were observed among treatments. Inclusion of EN in the diets increased (P  0.03) sorting in favor of large and medium particles and against small and fine particles. Plasma NO₃^- and NO2 - concentrations were elevated (0.06 to 3.68 mg/L of NO₃^- and 1.47 to 9.23 g/L of NO2 -; P < 0.01) with EN in a dose response manner, but blood methemoglobin levels for all treatments were below 1%. Feeding EN increased (P < 0.01) NO₃^- concentrations in muscle, fat, liver, and kidney and NO₃^- concentrations of those were similar between 1.25% EN and 2.3% UEN. In conclusion, including up to 2.5% of EN on a DM basis in a finishing diet did not cause NO₃^- toxicity or health problems in a long term study. In comparison with supplemental urea, feeding EN improved feed efficiency despite increases in sorting against dietary EN. [ABSTRACT FROM AUTHOR]