Definition of "galloway"

but if you have no mercy upon them, yet ſpare your ſelfe, leſt you bejade the good Galloway, your owne opiniaſter Wit,

1641, John Milton, Animadversions upon the Remonstrants Defence against Smectymnuus; republished in A Complete Collection of the Historical, Political, and Miscellaneous Works of John Milton, […], volume I, Amsterdam [actually London: s.n.], 1698, page 164

‘Don't you remember a famous trotting galloway I had, two years ago, that I bought at Tattersall's, that would go fifteen miles within the hour?’

1792, Charlotte Smith, Desmond, Broadview, published 2001, page 173