Horsehide has been the favorite leather for strops for the past 200 years because it has a significantly more dense fiber structure than any other generally available leather. There are leathers that are 'stronger ' and more 'supple,' such as Kangaroo, which is why that is preferred for whip making and lacing, but it's not nearly as dense and firm as horsehide. Buffalo hide, especially water buffalo, is very dense, but tends to be lower in silicate levels than horsehide due to the natural silicates found in the grazing areas where water buffalo tend to be found. I know in the rural area where I live, farmers usually herd their buffalo along the sides of roads to eat the grass and weeds growing there. That way they don't have to pay for feed. Good enough to sustain the animals, but not particularly silicate-rich food when compared with Kentucky Blue Grass, alfalfa, clover, timothy, etc., etc. It is the very dense fiber, compacted further by the processing, that makes the 'structure' of the horsehide strop so desirable. Add in the high silicate count and you get a strop that works well as a final step in the sharpening process without the need to add compounds on top of it.
Vegetable tanned Cowhide, 'steer hide,' buffalo hide, etc., can all be processed, effectively compressing the fibers either by the Cordovan process or at home simply with a rolling pin on dampened leather, but will not have as high a silicate count as horsehide, thus not be 'quite' as effective without compound. They WILL produce the same edge as horsehide, but it will take at perhaps half again as many strokes to achieve it. Horsehide isn't magical. It's just dense and has a high silicate level which makes it superior to other products for use as a strop without compounds. Frankly, the average knife sharpener will get just as good results using less expensive cowhide, especially as most knife sharpeners want to use compounds. Covering up horsehide with compound negates much of its primary value.
As I said before, you can't make 'shell cordovan' from buffalo leather, but you can compress the stuff and dye it burgundy color if you wish to.
I have made strops from horsehide, cowhide, buffalo hide, and kangaroo hide. All of these have been vegetable tanned hides. When being used WITHOUT compounds, my personal experience has been that horsehide worked best, cowhide second. When used WITH compounds, my personal experience has been that horsehide, cowhide, and buffalo hide all work equally well. As long as the hide can be made dense and firm as a substrate for compounds, the results were about equal.
