Effects of encapsulated nitrate on enteric methane production and nitrogen and energy utilization in beef heifers.

UNLABELLED: The objective of this study was to investigate effects of encapsulated nitrate (EN) on enteric methane emission and N and energy utilization in beef heifers. Eight ruminally-cannulated beef heifers (451 ± 21 kg BW) were used in a replicated 4 × 4 Latin square design. Four experimental diets were prepared and fed once daily for ad libitum intake: control, 1%, 2%, and 3% EN (0.15, 0.9, 1.5, and 2.5% NO3(-) in dietary DM, respectively). The control diet (55% forage and 45% concentrate) included encapsulated urea, which was gradually replaced with EN for the EN diets (iso-nitrogenous; 12.5% CP). In each period, EN was increased stepwise by 1% every 4 d during adaptation. A 7-d washout period (control diet offered to all heifers) was provided between experimental periods. Dry matter intake tended to decrease (10.4 to 10.1 kg/d; linear, P = 0.06) with EN levels. Enteric methane yield was linearly decreased (21.3 to 17.4 g/kg DMI; P < 0.01) by EN, and methane production (g/d) recovered to the level from heifers fed the control diet on the first day when EN was withdrawn from the diet. Apparent total-tract digestibility of DM and OM increased (P = 0.03) or tended to increase (P = 0.06), respectively, with EN levels. Starch digestibility tended to be greater (P = 0.07) for EN vs. CONTROL: The concentrations of rumen ammonia-N and plasma urea-N decreased linearly (P < 0.01) with EN. Total urinary N and urea-N excretion as proportions of N intake were linearly decreased (46.3 to 41.4%, = 0.09 and 37.1 to 29.9%, P = 0.01, respectively) with EN addition. However, NO3(-)-N excretion in urine increased linearly (P < 0.01) with EN levels. Fecal N excretion was not affected (P = 0.47) by EN, although fecal NO-N excretion increased linearly (P < 0.01) with inclusion of EN (0.09 to 0.88% of total N, P < 0.01). Retained N tended to be increased (percentage of N intake; 16.6 to 21.4%, = 0.08) by the EN. Supplementary EN lowered (6.64 to 5.46% of GE intake [GEI], P < 0.01) energy losses by enteric methane mitigation, which increased ME supply (calculated; 56.5 to 58.8% of GEI, P = 0.01) without changes in calculated heat production (P = 0.24). As a result, retained energy tended to increase (P = 0.07) with EN levels. In conclusion, feeding EN to beef heifers lowered enteric methane production in a dose-response manner, which slightly increased energy supply. Total urinary N excretion was lowered for EN due to lower urinary urea-N excretion.