The aim of high-profitability grazing systems is to produce milk efficiency from grazed pasture. There is very limited information available on the milk production capacity of dairy cows offered a grass-only diet for the main part of her lactation. In this study, spring-calving dairy cows were managed to achieve high milk production levels throughout the grazing season without supplementation. The calving date of the herd was 12 April; the herd had access to grass as they calved and remained full-time at grass until 20 November. During this period the herd produced 5,513 kg milk, while receiving 130 kg concentrate supplementation. The herbage mass offered was maintained at 1,490 kg dry matter ha‑1 (>3.5 cm) and the herd grazed to 4.5 cm across the grazing season. The weekly milk production performance achieved was then compared to the Herd Dynamic Milk model. The root mean square error (RMSE) and relative predicted error (RPE) for milk yield (as expressed weekly across lactation) was 1.47% and 6.09%, respectively, for body condition score the RMSE and RPE were 0.093% and 4.14% respectively. Offering spring-calving cows high levels of high quality grass resulted in excellent animal performance, however, this can be achieved with very good daily grazing management.