Effects of oral administration of dicyandiamide to lactating dairy cows on residues in milk and the efficacy of delivery via a supplementary feed source

•Metabolism stall studies investigated fate of administering DCD to cattle.•Recovery of DCD in urine was 61–82% with 10–19% in faeces and 1.2% in milk.•Rapid depletion of DCD in milk and excreta occurred after ceasing administration.•Provision of DCD in silage is a viable delivery method to cattle.•Administration of DCD to lactating dairy cows results in low amounts in milk. A metabolism stall study examined the fate of dicyandiamide (DCD) administered to dairy cows by either oral drenching or via a supplementary feed source (pasture silage) as a practical method to achieve targeted DCD excretion in individual urinations to reduce nitrogen (N) losses from grazed pasture systems. The study consisted of two experiments; firstly, lactating dairy cows were orally administered an aqueous solution of DCD at two rates (3 or 30gcow−1day−1) to examine the output in urine, faeces and milk, and secondly, non-lactating dairy cows were fed pasture silage amended with fine-crystalline DCD powder (30g DCD cow−1day−1) to investigate concentrations of DCD in excreta (urine and faeces) and the subsequent inhibition of nitrification of urinary-N in soil. Administration of DCD to lactating dairy cows in solution resulted in DCD being predominantly recovered in urine at 61% relative to 19% in faeces and 1.2% in milk (SEM 2.3, 1.0 and 0.08, respectively). Increased DCD administration rate led to higher (P