Grass-legume mixtures for improved persistence, biomass production, and intake by dairy cattle on pasture

The percentage of dairy farms in Wisconsin and Minnesota that employ managed grazing has increased dramatically over the last 20 years. The primary reasons have been relatively low startup costs and improved profitability associated with pasture-based dairying. A major biological limitation to profitability of grazing dairy operations is low forage intake by grazing cows relative to that obtained in confinement operations. This is related to pasture sward density, seasonal yield distribution and growth rate—all functions of plant species in the pasture as well as management and environmental conditions affecting plant growth. Based on our results, our environment will require several types of pasture to optimize full season production. Genetic advances have been made in both pasture grasses and legumes that allow development of mixtures that are capable of supporting greater levels of livestock performance than currently achieved by livestock graziers. A total of 21 different combinations of improved grass and legume species/varieties were evaluated on two university research stations in WI and MN. Results indicate that best seasonal distribution of yield was obtained with tall fescue, meadow fescue, and orchardgrass, with reed canarygrass intermediate, and smooth brome grass, quackgrass and Kentucky bluegrass demonstrating poor seasonal distribution of yield. Sward height and density were greater in nitrogen fertilized grasses than in mixtures with either Kura or white clover. And yield was also greater in nitrogen fertilized grasses than mixtures with legumes. Mixtures always had greater nutritive value, including greater crude protein and digestibility and lower fiber concentrations. Farmers are aware of the greater forage quality and the biologically fixed nitrogen that Kura clover contributes to pasture systems. They recognize the value of legume persistence, but some have had difficulty with establishment.

Introduction:

Profitable livestock production from pasture depends on the quantity and quality of forage produced, the capacity of the animal to harvest and utilize that forage efficiently, and the ability of the producer to manage the pasture resource. Environmental conditions, forage species, and pasture management decisions can affect forage productivity and sward structure, and therefore affect animal intake and performance. In dairy grazing systems, milk production may be limited by the opportunity for cows to consume enough pasture dry matter to meet their requirements for high levels of milk production. Stocker beef steers have similar nutritional requirments to support efficient weight gains on pasture. The amount of forage on offer and the physical characteristics of the pasture sward are two factors that have been shown to limit intake by cattle. These have not been systematically studied in pasture species or mixtures relative to the dairy and steer grazing industries in the North Central USA.

There is substantial evidence that sward structure influences intake and therefore there is need to better understand sward structure in grasses and grass-legume mixtures adapted to the northern USA. It is likely that sward structure is altered by addition of legumes to grasses, but this is not well understood. And the positive relationships between sward height and intake reported above for ryegrass will likely not hold for grass species that produce vegetative stems in aftermath growth. It is a worthy goal to characterize sward structure for pasture species adapted to the North Central Region, and we believe that there are large differences. Future research will elucidate the impact on dairy cattle performance in the north.

Forage budgeting on pasture, the balancing of forage production and use, requires knowledge of plant growth rates, seasonal distribution of yield, and anticipated consumption by cattle. Lack of a sound database for growth rates has resulted in broad and often misleading recommendations across the myriad of species used in northern pastures. Thus, pastures are often under-grazed in spring and overgrazed in the summer and fall. This results in less than optimal animal performance because of over-mature forage in late spring and inadequate forage availability in late summer and fall.

Although there is a long history of forage grass and legume breeding in the North Central USA, many of the cultivars were developed under mechanical harvesting conditions, have not been adequately evaluated under grazing, and their suitability for pasture has been questioned. A number of relatively recent additions to the arsenal of forage species that have potential for pasture production in Minnesota and Wisconsin include a persistent white clover variety developed under grazing in Wisconsin, kura clover, a meadow fescue ecotype extensively naturalized in Wisconsin, a more persistent orchardgrass variety developed in Wisconsin, endophyte free tall fescue, and a high yielding quackgrass variety developed in Minnesota. We have very little information on the relative performance of these or more common species and varieties grown alone or in binary grass-legume mixtures under grazing in the North Central USA.