Effects of encapsulated nitrate on nitrogen utilization and enteric methane emissions in beef cattle

Abstract Text: Effects of encapsulated slow-release nitrate (EN; GRASP Ind. & Com. LTDA, Paraná, Brazil) on nitrogen (N) utilization and enteric methane emissions in beef cattle were investigated. Eight ruminally-cannulated beef heifers (452 ± 21 kg BW) were used in a replicated 4 × 4 Latin square design. The basal diet (55:45 forage:concentrate ratio) included encapsulated urea [EU; 1.2% of dietary DM; Prote-N^®; GRASP Ind. & Com LTDA] for the control diet. The EN replaced a portion of EU and limestone with 1, 2, or 3% EN (0.8, 1.5, and 2.3% nitrate) in dietary DM. The diets (iso-nitrogenous; 12.7% CP) were fed once daily ad libitum. Each period consisted of 21 d of adaptation in a stepwise manner followed by 14 days of sampling (total collection for 4 days and enteric methane measurements in environmental chambers for 3 days). Dry matter intake tended to decrease (10.4 to 10.1 kg/d; P = 0.06) slightly with increases in EN, but body weight was not affected. Enteric methane emissions and intensity were linearly reduced (183 to 145 g/d and 21.3 to 17.4 g/kg DMI; P < 0.001) with increasing dietary EN where a treatment × hour interaction was observed (P < 0.001). Methane emissions with greater treatment effects occurred 0-12 h after feeding when cows consumed 87% of total feed offered. Nitrogen intake was not affected by EN. Plasma urea-N was linearly decreased (12.5 to 10.9 mg/dl; P < 0.001) with increasing dietary EN. Urinary N excretion tended to linearly decrease (100.2 to 86.5 g/d; P = 0.056) and the proportion of N intake was linearly reduced (46.1 to 39.2%; P = 0.03) with increasing dietary EN. Urinary urea-N excretion and the proportion of N intake were linearly decreased (75.9 to 56.2 g/d, P = 0.019 and 35.2 to 25.4%, P = 0.015, respectively) with increasing EN level. Fecal N excretion was not affected by EN. As a consequence, total N excretion and the proportion of N intake were linearly decreased (P = 0.047 and P = 0.001, respectively) with increasing dietary EN. In conclusion, supplementary nitrate in a protected form lowered enteric methane emissions in a dose-response manner. Urinary N excretion was reduced for heifers fed EN compared with EU, due to lower urea-N excretion in urine. The study demonstrates that feeding EN as a N source is environmentally beneficial compared with EU in beef cattle.

Keywords: encapsulated nitrate, enteric methane emissions, nitrogen utilization