2010 Annual Report 1a.Objectives (from AD-416) The objective of this cooperative research agreement is to obtain in vivo digestibility measurements for forages that will be harvested in small amounts. The U.S. Dairy Forage Center (USDFRC) is involved in several projects to improve the protein utilization, intake and digestibility of forages through selective breeding and genetic modification of germplasm. These novel forages have been evaluated by laboratory chemical and in vitro analyses and are at the stage where they should be tested for animal responses. Although dairy cows are the expected primary consumer of these forages, there are inadequate amounts of material available during early stages of germplasm development for evaluation by lactating cows. Young lambs, with intakes as a percentage of body weight that are similar to those of lactating dairy cows, will be used as model ruminants for the initial in vivo evaluation of these unique forage materials. Advantages of using lambs include: less feed per trial (~750lbs); smaller animal housing area and area maintenance; and ability to feed 100% forage legume diets; and economical research costs. The University of Wisconsin, Department of Animal Sciences (UW-AS) has the facilities and personnel for measuring digestibility of diets using lambs, and is interested in research on the in vivo evaluation of feeds. 1b.Approach (from AD-416) Multiple 5-week digestibility trials will be used to evaluate the forages and diets. Feces will be collected using fecal collection bags with lambs in individual metabolism crates. In some trials urine will also be collected. Each trial will include a short adaptation period followed by a covariate ad libitum intake and digestibility measurement using a reference alfalfa hay. The lambs will be adapted to the test forage for 14 days that will be followed by a 5-day ad libitum intake and digestibility measurement. The animals will be restricted to 1X maintenance intake for 2 days that will be followed by a 5-day restricted intake and digestibility measurement. Two groups of at least 18 lambs will be used. When not in metabolism crates, lambs will be housed in pens and fed alfalfa silage to adapt them to test forages. When in the crates, the UW-AS will measure and record feed offered and refused and fecal weights for each lamb daily. During fecal collection periods, a 20% aliquot of feces (and a 100 ml sample of urine, when appropriate) will be collected daily as well as samples of feeds offered and refused. Samples will be stored in a freezer during collection. Feeds or forages will be provided by the USDRFC. Feed and fecal materials will be processed and analyzed by the USDFRC. The UW-AS will be responsible for combining USDFRC analytical data with daily feed, refusal and fecal weights to calculate intake and digestibility. The USDFRC will be responsible for all data analysis and interpretation. 3.Progress Report Two feeding trials using lignin modified alfalfa hay and silage grown in Wisconsin were accomplished. One pasture grass feeding trial was conducted. Monitoring activities have included progress meetings among collaborators twice during the year and conference calls to provide supplemental information and to begin work on manuscripts; monthly assessment of the finances (with ARS administrative staff); and this annual report (AD-421).