Según el Simon & Schuster's Bilingüe.
Buena suerte y saludos del Oso ¶:^)

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Note added at 2005-05-08 23:57:13 (GMT)
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\"...***The breast-strap*** came into use by the 6th century in Germany.
Breast Strap Harness
[White 1962. p. 61] This harnessing technique moved the load-point to the horse\'s chest, thus removing the stress on the neck and allowing the horse to develop much greater power. Nevertheless, the breast strap was not a perfect solution as it tended to ride up to the neck under pressure from a load attached high on the back. To counter this the breast strap was held down by another strap that passed from it, between the front legs of the horse, and then to a girth strap. In addition, the load was attached to the breast band as low as possible. All of this served to allow the chest, rather than the neck, to be the contact between the horse and the load. [Derry and Williams 1960. p 201]

The breast-strap was followed a few centuries later by the introduction of the horse collar. The horse collar seems first to have been used in Europe around the 8th or 9th century [White, p. 61]. This may have been a northern European development or, as both White [White 1962. p 61] and Usher [Usher 1954. p 183] suggest, imported from the east. The horse collar rests on both the shoulders and the breast of the horse. The traces and thus the traction points, are over the horse\'s shoulders, not high on the horse\'s back. This allows the horse to develop much more power without putting any pressure on its neck. ...\"

http://scholar.chem.nyu.edu/tekpages/harness.html