Among various other studies, he performed breeding experiments with horses and zebras, well before the rediscovery of Gregor Mendel's works. Ewart crossed a male zebra with a female pony to show that the theory of telegony inherited from the Greeks was unsound. Telegony held that a female with a history of mating with multiple males would pass on genetic qualities of all previous partners to her offspring. Ewart later bred the mare which had produced zebra-horse hybrids with a pony, and the offspring showed no zebra qualities in either markings or temperament. Ewart's goal was also to produce a draught animal for South African conditions, resistant to African diseases and more tractable than a mule.
In 1883 he commissioned George Washington Browne to design a grand new house in Penicuik which is where he died. This was finished in 1885. It is now the Craigiebield House Hotel.