2008 Annual Report 1a.Objectives (from AD-416) The objectives of this cooperative research project are: . 1)develop a beef cow-calf production system using improved cultivars of grasses and legumes for irrigated pasture application that allows for extended high carrying capacity grazing facilitating the possibility of calving on a quarterly basis instead of once yearly;. 2)evaluate livestock preference of pasture legumes and grasses and relative animal performance; and. 3)use livestock grazing pressure as a selection tool to breed for persistence of birdsfoot trefoil, alfalfa, tall fescue, timothy, and meadow brome. 1b.Approach (from AD-416) Improved germplasm from ongoing ARS programs and breeding populations under investigation will be established in small and large scale research plots. Large scale plots will be used to determine animal performance, carrying capacity and species preference based on weight gain and time spent grazing each species. Small plots will be grazed to determine animal preference among plant genotypes and relative persistence among plant genotypes under heavy grazing. Livestock preference, dry matter production and plant persistence under grazing will be utilized in plant improvement programs. 3.Progress Report Four improved, irrigated pastures were established with either grass monocultures or mixtures of grasses and legumes on which three studies are now being conducted. This includes. 1)Weaned fall-born beef calves grazing meadow bromegrass and sainfoin with the objective to determine the feasibility of finishing grazing calves;. 2)Twenty-four spring-calving, cow-calf pairs divided in groups grazing (i) a pasture seeded to a monoculture of tall fescue grass only; (ii) a second group grazing the same tall fescue grass where the calves are receiving a supplement; (ii) a third group grazing tall fescue, alfalfa, and birdsfoot trefoil, and (iv) the fourth grazing tall fescue, alfalfa, birdsfoot trefoil where the calve are receiving a supplement; and. 3)A “fetal programming” study with twelve pregnant fall-calving cows grazing pastures identical in composition to #2, where one half receives pasture only and one half a supplements. Marbling is the basis of USDA Quality Grading, and is an indicator of high beef quality. It is hypothesized that if a gestating cow is supplemented with a starchy feed, the development of the unborn calf will be altered in such a way that it will marble much earlier than normal. Studies have been established on tall fescue, birdsfoot trefoil, and timothy. Similar experiments to on birdsfoot trefoil and tall fescue were established to characterize heritability differences when selection is performed among grazed and ungrazed treatments to increased efficiency of selection in breeding these species. An experiment has been established to characterize the preference of cattle for tall fescue genotypes with softer leaves relative to other standard types to increase the palatability of tall fescue. Additionally, a study to characterize relative differences among available timothy germplasm in response to defoliation was established. Monitored by meetings, phone calls, and site visits.