Readers of "Black Beauty" will be familiar with descriptions of the bearing rein. Its sole purpose was to improve the bearing (deportment) of a carriage horse. A horse naturally lowers its head and stretches its neck when pulling a load, horses wearing a bearing rein cannot easily pull a load. This image from 1909 shows a horse with and without a bearing rein and firmly states that it is a cruel device.

A milkman's horse knocking at a customer's door.