55 April 24 and 25, 2007 Tri-State Dairy Nutrition Conference Factors Affecting Manure Output on Dairy Farms William P. Weiss 1 , Normand R. St-Pierre, and Lynn B. Willett Department of Animal Sciences The Ohio State University 1 Contact at: 1680 Madison Ave., OARDC, Wooster, OH 44691, (330) 263-3622, FAX: (330) 263-3949, Email: weiss.6@osu.edu Summary The amount of manure produced on dairy farms can affect the financial bottom line. Labor, equipment, and facilities are needed to move and store manure, all of which have a cost. Increased output of manure can represent losses in potentially digestible nutrients (increased feed costs). Lastly, the environmental impact of dairy farming is strongly related with the quantity and composition of manure produced. Based on our research, the average lactating cow fed a typical Midwestern diet produces about 150 lb/day of manure (in our measurements, no bedding is used so manure is only the sum of feces and urine). Dry matter intake and manure output have a strong positive relationship. On average, manure output increases approximately 3 lb of manure per additional pound of intake. Although, on average, manure output increases as milk production increases, the relationship is not very strong, which means we can have high milk production without necessarily increasing manure output. Indeed, because cows produce manure even when they are not lactating (approximately 84 lb/day), high producing cows usually produce less manure per pound of milk than low producing cows. The dietary factor that had the greatest effect on manure production in our data set was the ratio of corn silage to haycrop forage. As the percentage of forage that was corn silage increased (resulting in a decrease in the percentage of haycrop forage) urine output decreased substantially, resulting in a significant decrease in manure output. As the percentage of forage as corn silage increased 10 units (and haycrop decreased 10 units), manure output decreased by about 4 lb/day. Introduction Manure is an inevitable byproduct of the production of milk. Although manure can be a valuable resource for crop production, it also has associated costs and excessive production of manure can adversely affect profitability of a dairy farm. Manure must be moved from the pens, stored, and then moved to fields; all these operations require equipment, energy, and labor (i.e., money). Excessive production of manure also can mean that some dietary nutrients are not being digested efficiently, which can elevate feed costs. Lastly, society, and therefore, the government, is becoming increasingly concerned about the environmental impact of animal agriculture, and several states and the federal government have enacted regulations regarding manure nutrients. Current regulations are mainly concerned with excretion of specific nutrients (i.e., nitrogen and phosphorus). The influence of diet on excretion of those nutrients has been discussed at previous Tri- State Dairy Nutrition Conferences (Beede and Davidson, 1999; Broderick, 2005) and will not be covered in this paper. Profitability of a dairy farm often can be enhanced when feeding and management practices