A recent court filing claims that a herd of 200 milking cows produces as much waste as 96,000 people. Mike Van Amburgh, Professor, Cornell Department of Animal Science, and I have taught students about the comparison between waste from cows and humans in our animal science classes for many years, and we knew the calculation stated in the lawsuit was much too high. We decided to review the science and determine how the miscalculation was made.
To start, we researched the scientific literature for human excretion rates and used the Cornell Net Carbohydrate and Protein model to predict urine and feces excretion from a cow making 23,000 pounds of milk, which is about the NYS average for 2016. We also calculated the comparison on the basis of N and P excretion. In simple terms, on a wet basis, the average person excretes .4 gallons of waste per day, and a cow producing 23,000 pounds of milk excretes 16.8 gallons of manure per day. This means one cow produces as much manure as 42 people. Therefore 200 cows produce an amount similar to 8,400 people. On an N basis, the comparison is 1 cow to 35 people and on a P basis, 1 cow to 38 people.
When we reviewed the information and references provided in the court document, the source of the error is clear: the authors used an EPA fact sheet that reports a family of 4 generates about 1 pound DRY MATTER of solid waste per day AFTER treatment, and then compared this to the wet weight of urine and feces excreted by a cow. Clearly not an apple to apple comparison. This critical error results in an estimate of one cow compares to 480 people, more than 10 times the actual figure.
To read more, see: What’s Cropping Up: “Setting the Record Straight: Comparing Bodily Waste Between Dairy Cows and People.”