"We have celebrated per-animal production as if it is the Holy Grail of livestock production,” says Tom Field, director of the Engler Agribusiness Entrepreneurship Program at the University of Nebraska. “It serves as the basis for our sustainability message, our pride in being productive and the pride we take in feeding people.”

Increased production per animal unit has been the basis of economic survival, too. Since commodity prices hover around the cost of production, by and large, the only way to increase financial return is to increase production relative to the same or similar cost.

That means that economic sustainability hinges on the ability to increase per-animal production continually.

Consider an August 2012 report from the Council for Agricultural Science and Technology that examined agricultural production relative to land and water use. The report points out that beef production (kg/hectare) increased 72% from 1961 to 2003, while chicken and pork production increased 198% and 143%, respectively. Milk production increased 126%.

“Dairy producers changed management substantially,” Field says. “A dairy today looks nothing like a dairy in 1961. Today, dairy cows receive total mixed rations. They are milked on rotary parlors, 24/7. There have been dramatic improvements in sanitation and waste management. We have made dairy cows substantially more productive.”

As dairy production increased, though, reproductive performance and longevity decreased.

“What would happen if a dairy cow had the inputs and the ability to express her full genetic potential for milk production?” Field wonders. “Could her udder even stand up? At what point in time does the system collapse?”

In other words, there are biological and physiological limits that extend across species.

Consider racehorses and the Kentucky Derby.

Winning Derby times between 1920 and 1969 ranged from 2:00 minutes to 2:09. Winning times since 1970 have ranged between 1:59 (Secretariat in 1973) and 2:03. Of course, Secretariat was a once-in-a-lifetime horse, at least. One tangible difference he possessed was an extraordinarily wide stride angle that made for a rare stride length.