- Diverse pastures containing multiple species help extend the grazing season and reduce the reliance on one or two species to meet all the nutritional requirements of livestock. Planting pasture species in spatially separated adjacent strips can increase the proportion of pasture plants with certain agronomic and nutritional attributes such as tolerance to waterlogging and presence of condensed tannins. The higher pasture quality of pasture plants with high bioactive compounds often lead to improved milk yield and reduced environmental impact of dairy farming. Thus, in the current study, combinations of simple and diverse pasture mixtures in mixed and spatially separated pasture strips were evaluated for their effects on forage DM production (Chapter 3), DM intake, milk yields, N partitioning and methane emissions (Chapter 4). The study was conducted between 2017 and 2019 in Corvallis, Oregon. A 7.2-ha paddock was divided into three 2.4-ha blocks to serve as replicates for the experiment. Each block was divided into 4 subplots of 0.6 ha, which were randomly allocated to the following treatments: 1) a simple pasture mix (perennial ryegrass (Lolium perenne) and white clover (Trifolium repens)); 2) a simple pasture spatially separated; 3) a diverse pasture mix (perennial ryegrass, festulolium (X Festulolium braunii), white clover, birdsfoot trefoil (Lotus corniculatus), plantain (Plantago lanceolata) and chicory (Cichorium intybus)) or a 4) diverse pasture spatially separated. Simple pasture mixes were composed of perennial ryegrass and white clover, while diverse pasture mixtures contained perennial ryegrass, festulolium, white clover, birdsfoot trefoil, plantain and chicory. Total annual DM production of pastures in 2017-2018
growing season ranged from 9.0 to 11.5 t DM/ha. The effect of diversity on biomass production was not significant (P=0.17) while mixed pastures appeared to have greater DM yield than spatially separated pasture mixtures by 2.97 t DM/ha/y (P=0.07). The grazing trial was conducted for 21 days from 3 April to 24 April in 2019. Thirty-six mid-lactation Jersey cows were randomly assigned to one of four pasture treatments. Cows that grazed diverse pastures had higher (P<0.05) milk solids (2310 g/d) and milk protein (P<0.01; 883 g/d) yields as compared to those that grazed simple pastures (2083 g/d and 778 g/d, respectively). Spatial separation did not affect (P>0.05) DMI, milk yield, or milk components except lactose content of milk, which was lower (P<0.01) in spatially separated pastures. Although diversity did not affect (P=0.22) daily methane production (g/d), cows that grazed diverse pastures had lower (P<0.05) methane yields per DM eaten as compared to simple pastures. Cows that grazed diverse pastures had lower urine N (%) and urea content and lower daily N output through urine. Thus, pasture species diversity can increase the pasture yield in periods when perennial ryegrass and white clover are less productive and had positive effects on milk solid production and environmental impact due to decreased urine N output and methane emissions.
Keywords: species diversity, DM intake, methane emissions, N partitioning, plant secondary compounds