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By Derby day, unbeknownst to the giddy masses at Churchill Downs, a line of trucks bearing dead horse babies had formed outside Lexington's equine autopsy lab. And the lab, inundated with carcasses, had scrambled to make space, lining freezers and hallways with overflow horseflesh. Hours later, while Monarchos broke for the roses and all the gents in seersucker and ladies in hats fingered their bets, a common sight around Lexington became the flash of a vet-bound pickup, blood-spattered barn hands performing frantic mouth-to-mouth on stillborn foals in back. Which is about when this plague, which would come to be known as mare reproductive loss syndrome (or MRLS), hit Crestwood.

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Further confirmation of the plague's return doesn't come until later that week, a harried call from one of the region's many wide-roving vets (some of whom drive 6,000 miles [10,000 kilometers] a month), the 29-year-old Jeanette McCracken, or Dr. J. She's a sharp athletic blonde who likes to say, upon a first meeting, "What, you were expecting someone with an Afro who could dunk?" She's known to some as the vet who once spied a panhandler in need of money for "food and pet shots" and so pulled over to hand him an apple and vaccinate his dog. Now she sounds frazzled, almost weepy, and she speaks of perhaps not buying a house here as she'd planned, because if things continue to go badly, "the whole industry might have to relocate," given all the reports of fetal losses flooding in from Bourbon and Fayette and Woodford Counties to name but a few.

The response, at many farms, is dramatic. Where once some put off felling cherry trees (the caterpillars' favorite roost) because the work would be costly and no MRLS link had been proved, now even the most elegant farms, like Lane's End, owned by Will Farish, ambassador to the United Kingdom, buzz with hundreds of thousands of dollars' worth of chain-saw work. And every spare minute is given over to defensive chores like respraying fence lines and bringing in mares. What more can be done? At Sheikh Hamdan al-Maktoum's lavish Shadwell Farm, a small army of pickers has been mobilized to prune every caterpillar nest from the trees. More generally (and less expensively), the answer seems to be to carry on as usual, which, about now, means a lot of mingling at catered parties and running off with the kids—who traditionally get some Derby time off from school—to Churchill Downs.

From the backside, the track's profile suggests the lines of a Mississippi paddleboat. On the infield, the grass fills with bellowing college students, many of whom seem happiest when chugging sweet mint juleps and baring their chests. In the jockeys' room, short men with exquisite balance and gorilla-grip handshakes lounge about in towels, their lockers full of enough sugarless gum, strong cigarettes, and mouthwash to let you know that a) you're still in Kentucky where tobacco is king, and b) the practice of "flipping," or throwing up to make weight, still goes on. It's Derby day, and the jocks I spy in passing include Mark Guidry, the languid veteran from Louisiana, shortly after an interview in which he held up his callused palms and said, "I ain't got no baby hands, baby." The celebrated and serious Pat Day is here too. And the fidgety Puerto Rican jock Willie Martinez is tugging at his silks, after an interview in which he mumbled a few rap lyrics—"I got my mind on my money and my money on my mind"—before quietly explaining how it feels to go down in the pack, with your bones breaking under hoof and the taste of blood in your mouth. "This was two years ago, and I was afraid I'd punctured my lung, man, like I was gonna drown in my own blood. You forget how powerful these animals are. But I've got friends who've been paralyzed, and so now, any race I walk away from, I'm like, 'I'm so lucky,' you know?"

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