The objective of this study was to quantify the farm gate nitrogen (N) off-set potential of perennial ryegrass (Lolium perenne L.; PRG) white clover (Trifolium repens L.; WC) swards by comparing the herbage and milk production from dairy farmlets that were simulations of full farming systems. A study was established where 120 cows were randomly assigned to 4 farmlets of 10.9 ha (stocking rate: 2.75 cow/ha), comprised of 20 paddocks each. Cows were fed 526 kg DM of concentrate on average each year. The 4 grazing treatments were PRG-only at 150 or 250 kg N/ha and PRG-WC at 150 or 250 kg N/ha. Cows remained in their treatment group for an entire grazing season and were re-randomized as they calved across treatments each year. As cows calved in the Spring as standard practice in Ireland, they were rotationally grazed from early-February both day and night (weather permitting) to mid-November, to a target post-grazing sward height of 4.0 cm. Mean sward WC content was 18.1 and 15.4% for the 150 and 250 kg N/ha WC treatments, respectively over the 3 year period. When WC was included, lowering the N rate did not reduce pre-grazing yield, pre-grazing height or herbage removed but did so significantly when WC was absent. Total annual herbage DM production was 13,771, 15,242, 14,721 and 15,667 kg DM/ha, for the 4 treatments; PRG-only swards receiving 150 kg N/ha or 250 kg N/ha and a PRG-WC sward receiving 150 kg N/ha or 250 kg N/ha respectively. In addition, when WC was present, compressed post-grazing sward heights were lower (4.10 vs. 4.21 cm) and herbage allowance (approximately 17 kg/cow feed allocation per cow per day) higher than the high N control (+ 0.7 kg of DM/cow per day). There was a significant increase in milk production, both per cow and per ha (P > 0.001), when WC was included into PRG swards. Over the 3-year study, cows grazing PRG-WC had greater milk (+ 304 kg) and milk solids (MSo; + 31 kg fat + protein) yields than cows grazing PRG-only swards. This significant increase in milk production suggests the inclusion of WC in grazing systems can be effectively used to increase milk production per cow and per ha and help offset nitrogen use. This result offers potential to increase farm gate NUE, and reduce the N surplus compared with PRG-dominant sward grazing systems receiving 250 kg N/ha without negatively impacting on MSo yield or herbage production and increasing farm profit by €478/ha.