Effects of encapsulated nitrate on growth performance, nitrate toxicity, and enteric methane emissions in feedlot beef steers: Backgrounding phase.

A backgrounding feedlot study was conducted to examine the effects of feeding encapsulated calcium ammonium nitrate (EN) on growth, enteric methane production, and nitrate (NO3 -) toxicity in beef cattle. A total of 108 crossbred steers (292 ± 18 kg) were blocked by BW and randomly assigned to 18 pens. The pens (experimental unit; 6 animals per pen) received 3 dietary treatments: Control, a backgrounding diet supplemented with urea (0.2% NO3 - and 0.9% urea in dietary DM); 1.25% EN, control diet supplemented with 1.25% EN (1.2% NO3 -) in dietary DM, which partially replaced urea; or 2.5% EN, control diet supplemented with 2.5% EN (2.3% NO3 -) in dietary DM, fully replacing urea. Twenty four steers were allocated to additional 4 pens and randomly assigned to 1 of the above 3 dietary treatments plus a fourth treatment: 2.3% UEN, control diet supplemented with 2.3% unencapsulated NO3 - (UEN; 2.4% NO3 -) fully replacing urea. Animals in the additional 4 pens were used for methane measurement in respiratory chambers and the pens (except UEN) were also part of the performance study (i.e., n = 7 pens/treatment). The experiment was conducted for 91 d in a randomized complete block design. During the experiment, DMI was not affected by inclusion of EN in the diet. Changes in BW, ADG, and gain:feed were not observed (P ≥ 0.57) by feeding EN. Methane production (g/d) tended to decrease (P = 0.099) by NO3 -(188, 174, 156, and 152 g/d for Control, 1.25%, 2.5% EN, and UEN, respectively), but yield (g/kg DMI) did not differ (P=0.56) among treatments. Inclusion of EN in the diet increased (P ≤ 0.02) sorting of the diets in favor of large and medium particles and against small and fine particles resulting in considerable increases in NO3 - concentrations of orts without affecting DMI. Plasma NO3 - and NO2 - concentrations increased (P ≤ 0.05) for EN compared with Control in a dose response manner, but blood methemoglobin levels were below the detection limit. Nitrate concentration in fecal samples slightly increased (from 0.01% to 0.14%; P < 0.01) with increasing levels of EN in the diet. In conclusion, EN can be used as a feed additive replacing urea in beef cattle diets during the backgrounding phase without NO3 - intoxication or any negative effects on growth performance. In addition, the study confirmed that feeding EN tended to decrease enteric methane production in the long term. [ABSTRACT FROM AUTHOR]