The article you linked doesn't support your anecdote about the root of the Shire Horse. It describes their history dating back centuries before railways. Their biggest use seems to have been hauling material to and from ports, not trains.
Sure it does. Shires go back a ways, but they were not bred in quantity until the 1850s or so. "In the late nineteenth and early twentieth centuries, there were large numbers of Shires, and many were exported to the United States."
Before and after that period, those big guys were an exotic breed. That's the railroad but pre-truck period.
(I've owned a Percheron, and have known some Shires.)
When you cite a source for something, the source should justify the thing you're claiming. The relevant part of your post to the thread was that "The 19th century solution was to develop a bigger breed of horse." It is entirely contrary to what the Wikipedia article says - "The breed was established in the mid-eighteenth century, although its origins are much older".
(relatives have owned Friesian's and Clydesdale's and Norwegian Fjording Horses, but it's neither here nor there)
That other definition doesn't really seem to fit either, but I acknowledge that if they had used a different word ("adopted a bigger breed" or "popularized a bigger breed" or something) then it would fit with the anecdote.
In working animal husbandry, breeds are rarely static and are typically selectively bred for the task at hand. As that task or its environment evolves, the breed is further developed or even forked to accommodate the new conditions.
So I think “developed” is fairly appropriate here, though “adapted” might have been more clear.
