Factors Affecting Manure Output on Dairy Farms

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.