2007 Annual Report 1a.Objectives (from AD-416) The objective of this cooperative research project is to perform a joint study to test the hypothesis that producing and feeding Low DCAD forages will prevent hypocalcemia in dairy cows. 1b.Approach (from AD-416) Decreased feed intake is a known problem when anions, such as Cl and S in the form of inorganic salts are added to prepartum rations. Preliminary data from our laboratory suggests that CaCl2 fertilization of several cool season forage species results in significant elevations in plant tissue Cl and a corresponding reduction in forage DCAD. The decrease in DCAD was due solely to an increase in plant Cl. The proposed experiment will be designed to determine if Cl incorporated into the plant matrix is as effective as inorganic salts at creating a mild metabolic acidosis in cows. Low DCAD hay will be produced by fertilizing in the spring with CaCl2 at the rate of 100 lbs. of Cl/acre. Control (high DCAD) plots will not receive CaCl2. This study will involve incorporation of the experimental hay into transition cow diets. We will utilize 36 cows entering into their third or greater lactation. The cows will be divided into 3 groups of twelve each (5 Jerseys and 7 Holsteins). The experimental hay will be incorporated into the transition diet at the rate of 5-6 kg/d. Groups 1 and 3 will receive the low DCAD hay and enough HCl to achieve a DCAD of -50 meq/kg. Based on our current estimates, the low DCAD hay will supply ~ 1.0 equivalent more of Cl relative to the high DCAD hay, therefore reducing the amount of HCl required to reach a DCAD of -50 meq/kg by about 50%. Group 2 will receive an equivalent amount of the water/molasses mixture but no HCl. We anticipate that the reduction in inorganic Cl will result in a more palatable ration and therefore more consistent feed intake, as well as better control of the cow's acid base balance. 3.Progress Report This report serves to document accomplishments under a Specific Cooperative Agreement between ARS and Iowa State University. 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. Project will resume by December 31, 2007. Progress will be monitored via bi-monthly teleconferences and annual written reports.