•Dairy heifers were orally administered with dicyandiamide (DCD) at 3 rates over a 90-day continuous dosing period.•DCD did not affect heifer growth or measured blood metabolites.•Prolonged daily administration of DCD resulted in the sustained excretion of DCD in urine and inhibited nitrification in soil.•A 3-fold increase in the rate administered resulted in a similar increase in the level of DCD in urine and deposited in urine patches.•DCD application rate onto soils varied widely, and the variability increased with increasing dose rate administered. Oral administration of the nitrification inhibitor dicyandiamide (DCD) to grazing ruminants for excretion in urine represents a targeted mitigation strategy to reduce nitrogen (N) losses from grazed pastures. A field trial and allied laboratory incubation study were conducted to examine the effects of oral administration of DCD to non-lactating Friesian dairy heifers on excretion of DCD in urine and efficacy in soil. Dairy heifers were orally administered DCD daily at three treatment levels (low, medium and high; 12, 24 and 36gDCDheifer−1day−1, respectively) and compared to a nil-DCD control group over a 90-day continuous dosing period. There were no adverse effects of DCD administration on heifer health or growth, as inferred by live-weight gain and measured blood metabolite levels. Prolonged administration of DCD to dairy heifers resulted in the sustained excretion of DCD in the urine over 90 days and inhibition of nitrification of urinary-N in the silty peat soil for up to 56 days (incubated at 20°C; P<0.001). Field soil sampling (0–75mm depth) of individual urine patches for DCD analysis revealed that a 3-fold increase in the rate of DCD administered resulted in a similar increase in the concentration of DCD voided in the urine and subsequently deposited in urine patches (median equivalent DCD application rates of 22, 36 and 59kgha−1 for the low, medium and high DCD treatment levels, respectively; P<0.001). However, large differences (up to 40-fold) existed between individual urine patches in the rate of DCD deposited at each treatment level, which showed a positively skewed distribution. This study highlights the viability of prolonged daily administration of DCD to ruminants for sustained excretion in urine and effective inhibition of nitrification in soil as a practical targeted mitigation technology to reduce urinary-N losses from grazed pastures.