If there were one thing Temple Grandin, who teaches animal science at Colorado State University, could change about the milk business, it would be the way the industry has messed with its cows.

"What they've done is basically the equivalent of taking a car, putting it in neutral, and then dropping a brick on the accelerator until it blows up," said Grandin. "These cows are constantly in the red zone."

Grandin is being slightly hyperbolic. No milk cow, to her knowledge, has ever exploded. But she insists the analogy is apt. And when one looks at what has happened to milk production over the past few decades, it's easy to see why.

Once a country dotted with dairy farms, the United States is now home to a select few milk makers (the number has fallen by almost 90 percent since 1970, according to data from the Agriculture Department). We are milking our cows for all they are worth.

The chart below shows the simultaneous fall in the number of milk cows and rise in the amount of milk each cow produces on average. There are almost 2 million fewer milk cows today than there were in 1980, but production has remained fairly stable. And guess who is shouldering the brunt of that load?

The answer, of course, is milk cows.

With bottom lines in mind, the industry has long pushed to get more out of its four-legged employees. For many years, that meant operational tweaks, such as changing barn design, altering what cows were fed and being fussy about things such as milking schedules. But more recently, it has meant screwing with the actual anatomy of the animals.

Holsteins, the majestic black and white cows that make up the vast majority of milk cows in the United States, don't look like they used to. In fact, we have altered their genetic makeup by 22 percent since the 1970s, as Modern Farmer noted in 2014. Today's cows are taller, heavier, have higher and larger udders, and tend to stand on differently shaped legs. And there's a growing sense we have gone too far.

This is how NPR recently described the rising tension:

Since dairy cows were first brought to the United States, their owners have been trying to coax more and more milk out of them. They've done that through dairy parlor design, barn layout, feed rations, milk scheduling and hormone treatments.
Now the focus is on genetics: Cows are being bred to be larger, hungrier, and more productive. But this drive to raise ever-larger, hulking Holsteins has some prominent livestock advocates ringing alarm bells.

In many ways, Grandin is one of those advocates. A longtime dairy-industry expert, she divides producers into two categories: the progressives and the not progressives. The former, which she says account for about a third of the industry, have moved away from the practice of breeding "milking machines," choosing to raise smaller cows that tend to be healthier, as well as productive over a longer period, and opting to feed their herds grass as often as possible. The latter, meanwhile, are driving up the efficiency numbers you see in the chart above, selecting for cows that tend to suffer from a number of adverse health outcomes.

"I call them the bad dairies," Grandin said. "They make up most of the farms in the United States, and their cows are so wrecked by the time they stop milking they can barely be used for beef."

The problem, she says, is not only a question of animal welfare—although that is certainly an important component. It's also compounded by the shortsightedness of the industry. Grandin believes the "bad dairies" are so obsessed with production that they are failing to properly consider the larger picture. Smaller cows might not produce as much milk as their larger counterparts, but they tend to live longer and be more fertile. Shifting away from the jacked up cows, in other words, could be better for both the farms and their animals.

Despite Grandin's conviction, her opinion is not shared by everyone in the industry. Many farmers, facing a highly competitive market and demanding American consumers, believe that selecting for certain genetic traits is crucial. What's more, they argue that it doesn't have to come at the expense of the animals.

“Dairy farmers have to be smart to survive. Better bovine genetics help dairy farmers raise healthier cows, which in turn produce higher-quality milk," said Jamie Jonker, who is the vice president of sustainability and scientific affairs for the National Milk Producers Federation, which represents more than 32,000 dairy farmers around the country.

He agrees that everyone loses when cows are unhealthy, but pushes back against the idea that cows are suffering in the way Grandin suggests.

"Not all want bigger cows; some prefer other traits, and thanks to genetics, they have choices," he said. "No farmers want animals that are unhealthy, because that’s bad for cows and even worse for their owners."

Earlier this year, Robert Behnke, a dairy farmer in Brooklyn, Wis., celebrated an incredible feat. One of his cows, a monstrous Holstein called Gigi, produced more milk in one year than any cow in recorded history, a mind-boggling 75,000 pounds, or nearly three times the industry average.

To many in the industry, Gigi, who is so large, "you can literally fit your head and shoulders between her front legs," according to Behnke, has become something of a cow hero. There are even glamour shots of the enormous — and impossibly productive — animal.

But to others, Gigi, or at least the obsession with her, is a sign of everything that's wrong with the milk business.

"You can push cows to the point where they start to fall apart, and that's what we're doing," said Grandin. "Cows are getting so big today, they don’t fit in anything, they don't fit in the 13-foot, 6-inch trucks the industry has used forever."

"And you know what?" she added. "If you want to fix a problem, you treat the root cause, not the size of the truck."

This article has been updated to include comment from the National Milk Producers Federation.