RESUMO
Achieving high animal productivity without degrading the environment is the primary target in pasture-based dairy farming. This study investigated the effects of changing the forage base in spring from grass-clover pastures to forb or legume-based pastures on milk yield, N utilization, and methane emissions of Jersey cows in Western Oregon. Twenty-seven mid-lactation dairy cows were randomly assigned to one of three pasture treatments: grass-clover-based pasture composed of festulolium, tall fescue, orchardgrass, and white clover (Grass); forb-based pasture composed of chicory, plantain, and white clover (Forb); and legume-based pasture composed of red clover, bird's-foot trefoil, berseem clover, and balansa clover (Legume). Pastures were arranged in a randomized complete block design with three replicates (i.e., blocks) with each replicate grazed by a group of three cows. Production and nutritive quality of the forages, animal performance, milk components, nitrogen partitioning, and methane emissions were measured. Feed quality and dry matter intake (DMI) of cows were greater (P ≤ 0.05) for Legume and Forb vs. Grass, with consequent greater milk and milk solids yields (P < 0.01). Cows grazing Forb also had more (P < 0.01) lactose and linoleic acid in milk compared with cows grazing the other pastures, and less (P = 0.04) somatic cell counts compared with Grass. Cows grazing Forb had substantially less (P < 0.01) N in urine, milk, and blood compared with cows grazing the other pastures, with not only a greater (P < 0.01) efficiency of N utilization for milk synthesis calculated using milk urea nitrogen but also a larger (P < 0.01) fecal N content, indicating a shift of N from urine to feces. Both Forb and Legume had a diuretic effect on cows, as indicated by the lower (P < 0.01) creatinine concentration in urine compared with Grass. Methane emissions tended to be less (P = 0.07) in cows grazed on Forb vs. the other pastures. The results indicate that Forb pasture can support animal performance, milk quality, and health comparable to Legume pasture; however, Forb pasture provides the additional benefit of reduced environmental impact of pasture-based dairy production.
