There are many differences in the characteristics of the hybrids. Mules can be larger. This is often the case because large draft horse mares and the largest "Mammoth" jacks are used as brood stock.
Mules born of smaller riding stock mares are not so large. We had a neighbor who kept a herd of fine Tennessee Walkers and a large jack. He raised and trained riding mules. They were fine boned, attractive, well behaved riding stock.
Mules are most easily identified by the large donkey like ears. A henny will have small petite ears like a horse. The only hennys I have been around were of small stature, but I have no idea of the lineage. It is quite possible they were bred from a male shetland pony and a female burro. Both, horses and donkeys come in various sizes and their offspring will reflect their lineage in that regard.
Thanks for the great explanation. I knew a guy back in the day that was into coon hunting. The guys in his hunting group would ride mules. He said his mule could go anywhere he wanted it to go.
