I love being invited to critique artwork, though I sometimes think maybe folks aren't asking for as much as I'm happy to dish out. but, you seem to be interested in a critique, so here goes . . .
I really love the coloration you use. it has a restrained quality that is like an old tintype or duagerotype (spell?) photograph. the use of sepia, brown and black is really appealing. and the linework , such as in the mane or shadowing of this one is classic:
I also will refer to that above image to say that I like very much that the horse is weight bearing in a beleivable manner. he is over his center of gravity, and he appears to have a skeleton under the flesh.
this is really, really important when you draw animals, (and people), especially being that have long legs/arms or large, complex skull. you really have to try and imagine the skeleton underneath. that means that legs need to read as the same length, as straight, as the same thickness, and if one leg/arm is bearing weight, then the connceting joint (shoulder or hip) will be HIGHER.
little things like that help to make a 2D drawing read as a 3D figure. and, when the figure is in motion, as the above, it is even harder.
I think the above figure is really a success.
I will say, that the same attention to the underlying skelelton needs to be placed on the skull. even though it is not articulated, it IS there, and how the eyes sit in the skull, visiable from the side in the above case, is very , very important. when I look at that horse's eye, I feel that is is positioned for a head that is not as severely angled downward as you have the head. that eye is too much on the top of the head. it needs to have been moved more downward and faceing more toward the horse's nose, instead of into upper space. also, the ears need to move forward , too, in this case. they are attached right at the poll, so if the horse has his head really tightly rolled over, the ears will be rolled well forward, too.
this attention to how the flesh lays over the skeleton is also evident in the dog picture:
if you really look at the eyes, they are not exactly in a line with each other, nor perpendicular to the line coming down from the nose, as they should be. one is higher than the other, and if you look at the skull, one side is higher, but the two things, eye and skull, don't line up with each other. you can have one eye higher than the other, but only in the case of a tilted head, in which case EVERY symmetrical part of the skull must follow that same tilt.
since the face IS symmetrical, it's essential that the angles of the eyes, the nostrils, the ears (well, not so much in dogs, since they move), but the teeth . . . you know what I mean. the face lines need to be parallel to indicate that these 'thing' you put in the face (eyes, mouth, nose) exist IN the skull, not just freely floating on top, without any connection to anything.
I often use a ruler or just the edge of a piece of paper to makes sure the eyes are lining up. even the PUPILS of the eye need to line up.
I've had many drawings that I spend a lot of time and intense focus on detail, when I stepped back and looked at them, have 'something' not quite right about them. when I really looked, it turned out to be this lack of correct alignment to the underlying bones. if it's minute, most people will not notice it, especially with lovely brush/pen work and color. but, I mention this to you becuse you DO have the talent, it's worth your effort to take the time to be accurate on this.
is the most accurate in terms of the nostrils and eyes linging up, (even in a 3/4 view) in perspective and in the skull. it also has a certain spark to the eye that makes it captivating to look at. If I had hired you for that portrait of my horse, I'd be THRILLED to have it on my wall!
well done. keep it up. you have talent.
PS consider that if the eyes have a 'shine spot', the shiny metal of the bit and buckles will also have a shine spot. details, details, but this is part of the tricks of 2D to 3D that makes things 'look' real.