The effect of dicyandiamide on rumen and blood metabolites,diet digestibility and urinary excretion

The excretion of urine by dairy cows provides a source of nitrogen (N) to pasture. Excess N from urine patches can be lost through nitrate (NO₃⁻) leaching and nitrous oxide (N₂O) emissions. Dicyandiamide (DCD) inhibits nitrification in the soil and is usually applied to the pasture by blanket spreading the entire field. This study assessed the potential of pulse-dosing cows with DCD so that the DCD will be excreted in the urine and deposited directly onto the urine patches. The objective of this study was to measure the recovery of DCD in urine and faeces and to assess the effects of DCD on rumen and blood metabolites and diet digestibility. Eight non-lactating Holstein–Friesian dairy cows fitted with rumen cannulae were assigned to two treatments in a Latin square design over two periods. The two treatments used were (1) control (CON) consisting of 500 ml distilled water and (2) DCD consisting of 0.1 g DCD per kg liveweight (LW) suspended in 500 ml distilled water. Both treatments were pulse-dosed into the rumen daily for 6 days with half the volume dosed in the morning and the remainder in the afternoon. The administration of DCD into the rumen had no effect on rumen and blood metabolites, and diet digestibility when compared to the control treatment, as all were not significantly different from the control treatment and were within the normal biological range. During 6 days of dosing with DCD the average recovery of the dosed DCD in urine was 82.3%, with a further 2.1% recovered in the faeces. No DCD was recovered in the urine and faeces 10 days following the cessation of dosing. These results could provide the basis for a novel mitigation strategy to reduce NO₃⁻ leaching and N₂O emissions from urine patches in grazed grassland.