2007 Annual Report 1a.Objectives (from AD-416) The objective of this cooperative research project is to test the hypothesis that combining the low calcium diet strategy with the low DCAD diet strategy for milk fever prevention to form a low calcium, low DCAD diet is more effective at preventing hypocalcemia than feeding either a low calcium diet or a low DCAD diet alone. 1b.Approach (from AD-416) Sixty Jersey and Holstein cows entering their third or greater lactation will be fed one of four diets in a randomized block design. Cows will be assigned to blocks based on expected calving dates by breed. We will have 5 Jerseys and 10 Holsteins in each experimental block. The four diets will consist of a low calcium-high DCAD diet, a low calcium-low DCAD diet, a high calcium-low DCAD diet, and a high calcium-high DCAD diet. The diets will be formulated using wheat straw (low in calcium and low in potassium), corn silage, and soybean meal as the main ingredients. This diet will serve as the basis for the experiment. Based on our current feedstuff analysis we can achieve a diet that is 0.4% calcium which should be capable of stimulating the parathyroid gland prior to calving. This diet will also be about 1% potassium. We will add enough magnesium to all diets to make them 0.4% magnesium. We will add enough chloride to this diet in the form of hydrochloric acid to bring the chloride to within 0.45% of the potassium content of the diet (as determined by analysis). Calcium in the form of calcium carbonate will be added to bring diet Ca to 0.8% in the high calcium diets and potassium carbonate will be added to raise DCAD to +250 mEq/kg in the high DCAD diets. Diets will be fed beginning four weeks before expected calving dates. Blood samples will be taken daily and urine samples weekly beginning two weeks before expected calving date and for the first two weeks of lactation to assess the effectiveness of the diets on the incidence and degree of hypocalcemia experienced by the cows. 3.Progress Report This report serves to document accomplishments under a Specific Cooperative Agreement between ARS and the NE Iowa Community Based Dairy Foundation. Additional details of research can be found in the parent project 3625-32000-085-00D, Molecular, Nutrient, and Endocrine Basis for Metabolic Diseases that Affect the Reproductive Health of the Dairy Cow. The project was scheduled to start September 26, 2006. Scientist has left the organization and there are no results to report. We plan to resume the work by December 31, 2007. Progress will be monitored via bi-monthly teleconferences and annual written reports.