Three Qualities are essentially necessary to make the Trot useful, it ought to be extended, supple, and even or equal; these three Qualities are related to, and mutually depend upon each other: In effect, you can't pass to the supple Trot, without having first work'd your Horse upon the extended Trot; and you can never arrive at the even and equal Trot, without having practised the Supple.
I mean by the extended Trot, that in which the Horse trots out without retaining himself, being quite strait, and going directly forwards; this consequently is the kind of Trot, with which you must begin; for before any thing else ought to be meditated, the Horse should be taught to embrace and cover his Ground readily, and without fear.
The Trot however may be extended without being supple, for the Horse may go directly forward, and yet not have that Ease and Suppleness of Limbs, which distinguishes and characterizes the Supple.
I define the supple Trot to be that in which the Horse at every Motion that he makes bends and plays all his Joints; that is to say, those of his Shoulders, his Knees and Feet, which no Colts or raw Horses can execute, who have not had their Limbs suppled by Exercise, and who always trot with a surprizing Stiffness and Aukwardness, and without the least Spring or Play in their Joints. The even or equal Trot, is that wherein the Horse makes all his Limbs and Joints move so equally and exactly, that his Legs never cover more Ground one than the other, nor at one Time more than another: To do this, the Horse must of necessity unite and collect all his Strength, and if I may be allowed the Expression, distribute it equally through all his Joints.
To go from the extended Trot, to the supple, you must gently, and by degrees, hold in your Horse; and when by Exercise he has attain'd sufficient Ease and Suppleness to manage his Limbs readily, you must insensibly hold him in, still more and more, and by degrees you will lead him to the equal Trot.
The Trot is the first Exercise to which a Horse is put; this is a necessary Lesson, but if given unskilfully it loses its End, and even does harm.
Horses of a hot and fretful Temper have generally too great a Disposition to the extended Trot; never abandon these Horses to their Will, hold them in, pacify them, moderate their Motion by retaining them judiciously, and their Limbs will grow supple; they will acquire at the same time that Union and Equality, which is so essentially necessary.
If you have a Horse that is heavy, consider if this Heaviness or Stiffness of his Shoulders or Legs is owing to a Want of Strength, or of Suppleness; whether it proceeds from his having been exercised unskilfully, too much, or too little. If he is heavy, because the Motions of his Legs and Shoulders are naturally cold and sluggish, tho' at the same time his Limbs are good, and his Strength is only confin'd and shut up, if I may so say, a moderate but continual Exercise of the Trot will open and supple his Joints, and render the Action of his Shoulders and Legs more free and bold; hold him in the Hand, and support him in the Trot, but take care so to do it, as not to check or slacken his Pace: Aid him and drive him forward, while you support him; remember at the same time, that if he is loaded with a great Head, the Continuation of the Trot, will make his Apuy hard and dull, because he will by this means abandon himself still more, and weigh upon the Hand. All Horses that are inclined to be remingue, should be kept to the extended Trot; every Horse who has a Tendency to be remingue is naturally disposed to collect all his Strength, and to unite himself; your only way with such Horses is to force them forward: In the Instant that he obeys, and goes freely on, retain him a little; yield your Hand immediately after, and you will find soon that the Horse of himself will bend his Joints, and go united and equally.
A Horse of a sluggish and cold Disposition, which has nevertheless Strength and Bottom, should likewise be put to the extended Trot; as he grows animated, and begins to go free, keep him together by little and little, in order to lead him insensibly to the supple Trot; but if while you keep him together, you perceive that he slackens his Action, and retains himself, give him the Aids briskly, and push him forward, keeping him nevertheless gently in Hand; by this means he will be taught to go freely and equally at the same time.
If a Horse of a cold and sluggish Temper is weak in his Legs and Loins, you must manage him cautiously in working him in the Trot, or otherwise you will enervate and spoil him. Besides, in order to make the most of a Horse, who is not over strong, endeavour to give him Wind, by working him slowly, and at Intervals, and by increasing the Vigour of his Exercise by degrees; for you must remember that you ought always to dismiss your Horse, before he is spent and overcome with Fatigue. Never push your Lesson too far in hopes of suppling your Horse's Limbs by means of the Trot; instead of this you will falsify and harden his Apuy, which is a Case which happens but too frequently.