2007 Annual Report 1a.Objectives (from AD-416) To determine how storage structure affects alfalfa silage dry matter losses and quality and subsequent intake and milk production by lactating dairy cows. The project is being extended to conduct the research over a third harvest season. "Salaries" are for student help; "Other Costs" are for ARS overhead. 1b.Approach (from AD-416) Two identical trials will be conducted in 2004 and 2005, using second- or third-cutting alfalfa. Alfalfa will be ensiled in one bunker silo (16' x 72' x 12'), one pressed bag silo (8' diam. x 170') and one oxygen-limiting silo (14' x 50'). Each load of alfalfa will be weighed, and a grab sample will be taken for moisture and quality analysis. All three silos will be opened and emptied at the same time after a minimum storage time of 60 days. All silage removed from each structure (both fed and spoiled) will be weighed and recorded. During the course of emptying the silos, a lactation trial will be performed, preferably under warm conditions. The trial will be a replicated 3 x 3 Latin square. Forty-five cows in early lactation will be used in the trial; 15 will be assigned to each diet. The diet will consist of 50% alfalfa silage and 50% concentrates, and will be balanced to the same NDF content across treatments. Cows will be fed individually in tie stalls ad libitum with approximately 10% refusal. Cows will be adapted to each ration for three weeks. In the fourth week, intakes and milk production will be recorded daily. 3.Progress Report This report serves to document research conducted under a Trust Agreement between ARS and Engineered Storage Products Company. Additional details of the research can be found in the report for the parent project 3655-31000-018-00D, “Completing An Expert System That Will Provide Site-Specific Nutritive Values For Feeds.” The goal of the project is to compare the losses and nutritive value of alfalfa silage made in three types of silos: bag, bunker and oxygen-limiting. Analyses of samples from the second trial were completed. Dry matter (DM) losses in the second year followed the same trend as in the first year. Average DM losses across both years were: oxygen-limiting silo (4.3%), bag silo (11.3%) and bunker silo (16.9%). Silage neutral detergent fiber (NDF) concentration and NDF digestibility were affected by silo type in the second trial. NDF was lowest from the oxygen-limiting silo (38.5% DM) and highest from the bunker (42.6% DM). NDF digestibility was 47.1% in the oxygen-limiting silo vs. 44.9% in the other two silos. The second trial silages were fed to lactating dairy cattle at 41% of the ration. Dry matter intake was higher on the oxygen-limiting silage treatment (23.0 kg/cow/d) vs. the other two treatments (21.5), but milk production was not affected by silo type. These results were different from the first trial where feeding the silage from the oxygen-limiting silo resulted in greater yield of 3.5% fat-corrected milk (2.6 kg/cow/day) than feeding the silages from the other two silos. The cooperators have been kept apprised of results, as they have become available through telephone conversations and email. The cooperators visited in May 2007 to discuss results and plan future research.