Grazing multispecies swards can have multiple benefits for the productivity and environmental sustainability of ruminant production systems. However, few studies have determined the effect of different sward-type systems on co-grazed cattle and sheep performance. The objective of this study was to determine the effect of different sward type systems: (1) a sown Lolium perenne (PRG) sward (receiving 170 kg of N/ha per year); (2) a pre-existing permanent pasture (PP) (receiving 135 kg N/ha per year); (3) a sown 6 species sward (6SP) with Lolium perenne, Phleum pratense, Trifolium pratense, Trifolium repens, Cichorium intybus and Plantago lanceolata (receiving 70 kg N/ha per year); and 4) a sown 12 species sward (12SP) with Dactylis glomerata, Lotus corniculatus, Onobrychis viciifolia, Achillea millefolium, Petroselinum crispum, Sanguisorba minor in addition to the 6SP listed above (receiving 70 kg N/ha per year); on the animal performance of co-grazed cattle and sheep. In 2020 and 2021, each sward-type system (9 ha) was rotationally co-grazed from April to November by dairy cross heifers (n = 20 per treatment per year, turned out at 395 ± 15 days of age, mean ± SD) and ewes (n = 22 ewes per treatment per year) plus lambs. Heifer live weight was recorded monthly, and heifers were drafted for slaughter when their estimated fat class on the EUROP grid scale reached 3-. Lamb live weight was recorded fortnightly, and lambs were drafted for slaughter at 42 kg (lambing to weaning), 44 kg (weaning to September) and 46 kg (after 1 September) to obtain a target carcass weight of 21 kg. Average daily gain (ADG) from turnout to slaughter was higher for heifers grazing the 6SP sward (1.09 kg/day) compared to all other sward types (12SP (0.99 kg/day), PRG (0.92 kg/day), and PP swards (0.92 kg/day); P < 0.001)). Lamb ADG from birth to slaughter in the 6SP (393 g/day) and 12SP (363 g/day) were greater than the PP (305 g/day; P < 0.001) or PRG swards (292 g/day; P < 0.001). Carcass dressing percentage was higher for lambs grazing the 6SP (48.5%) and 12SP (48.6%) compared to lambs grazing the PRG (44.7%; P < 0.001) and PP swards (44.6%; P < 0.001). Lambs grazing the 6SP and 12SP had a reduced number of grazing days from turnout to slaughter (82 and 93 days respectively) compared to the lambs grazing the PPG and PP swards (133 and 127 days respectively; P < 0.01). Overall, co-grazing multispecies swards improved heifer and lamb production performance at lower nitrogen fertilisation rates, potentially mitigating the environmental impact of beef and sheep production systems.