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

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 x 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EN, and methane production (g/d) recovered to the level from heifers fed the control diet on the first day when EN was withdrawn from the diet.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%, P = 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 NO3--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%, P = 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 doseresponse manner, which slightly increased energy supply. Total urinary N excretion was lowered for EN due to lower urinary urea-N excretion.