This study investigated the effects of diversification strategy through the inclusion of forb and legume based pastures in the feedbase of dairy cows on annual forage production, botanical composition, spring milk yield, N partitioning and methane emissions from dairy cows in Western Oregon. Using a randomized complete block design, 3 plots served as blocks. Those were subdivided into three pasture types resulting in 9 grazing plots, which served as the experiment unit. The pasture production component examined the productivity and species composition of three types of specialized pasture: grass-, forb- and legume-based pastures (Chapter 3). The second component of the study involved grazing dairy cattle on the three pasture types over two grazing periods and the feed intake, milk production, milk components, nitrogen partitioning and enteric methane production were measured (Chapter 4). A total of 27 Jersey dairy cows were randomly assigned to 9 grazing plots in 29 April. Cows were allocated approximately 16 kg/d of pasture with a post-grazing residual of 1300 kg of DM/ha in both periods. DMI, milk yield, composition, urine and fecal nitrogen output was taken on d 15, 18, and 21 and was repeated in the second period. Methane emissions were collected using the SF6 tracer method from d 16 to d 21 in the first grazing period. The total annual DM production of pastures were comparable (P=0.28). Grass based pastures had substantially higher (P < 0.05) early spring production that exceeded 3700 kg DM/ha. Whereas forb-based pastures had the highest (P < 0.05) summer DM yield at 4500 kg DM/ha with legume-based pastures around 4300 kg DM/ha. Herbage DMI was highest in cows that grazed legume-based pastures at 15 kg DM/cow/day and lowest in cows grazing grass-based pastures (P < 0.05). Legume-based pastures were the highest nutritive value with the exception of NDF which forb-based pastures had the lowest (P < 0.01). Legume-based pastures yielded between 22.7 – 23.1 L/d of milk, highest of the three treatments (P < 0.01). Milk fat content tended to be higher in legume-based pastures (P = 0.07) while milk protein content remained unaffected by pasture type (P = 0.31). Forb-based pasture diet decreased N (%) of urine substantially (P < 0.01) and increased fecal N (%) (P < 0.01). Microbial protein supply remained unaffected by treatment (P = 0.14). Methane emission tended to be decreased by forb-based pastures (P = 0.07). These studies indicate a potential of legume- and forb-based pastures to fulfill nutritional deficiencies in late spring in pasture based dairy production as well as a potential to reduce the environmental impact of pasture-based dairy production.