Bucky muttered, "I'm having puppies, not piglets. I don't need a sty."
"It's a whelping box," Steve said mildly. He penciled something, which was probably a measurement and not a comment about Bucky's mood, on one of the pages of diagram. Those were bound to be from the internet, unless Steve had found something really specialised up at the library. Printed out, wherever he'd got them, because Steve liked having everything on paper, not only his own drawings. The technical ability to annotate stuff on a StarkPad with a stylus, since they really were in the future, didn't end Steve's stubborn preference.
Steve shuffled a different page to the top of the stack, and ran his finger along one of the lines. "As it happens, Buck, these are called pig rails."
A feature named after the rails fixed in a sty to stop a sow from rolling on piglets. Once he had absorbed the explanation, Bucky was indignant. "As if I'd squash them!" He touched the slight curve of his belly, tenderly. He was barely showing, but proud to have a whole litter growing inside his science-built womb. He would keep the puppies just as safe after they were born.