No CGI even imagined let alone used back then but can speak to all those pain bay, medium size, medium to slightly heavier weight with very little white horses in early Western movies and TV shows filmed in So Cal. Pulling wagons, packing bad guys or bringing the law they all look the same. They did scrape up some pintos for Indians and fancier mounts for featured players…and those horses worked alot and are easily recognizable.
Learning to ride in the early 1960s, that was what I learned to ride on and that was what was the most commonly available type locally. Some that I rode had film experience and my early teachers were stuntmen, one doubled several popular leading men. Those horses were broke, broke, broke and those guys knew what they were doing.
The reason was until the mid 20th century the US Army bred horses specifically for the Cavalry. Because a flashy horse is an easier to find and shoot, they were plain, mostly bay, needed to physically be able to do multiple jobs in harness or under saddle. They also had to have a very, very willing temperment. Kind of an early Jeep.
Starting in 1918 the Army Remount service stood Stallions of various breeds, including TBs, and civilians brought their suitable type mares then sold the offspring back to the Army when they were ready to break to saddle. When they aged out, they trickled back into civilian service, some never made it into the Army and were sold as saddle and harness horses. This created a really nice, useful Grade horse.
As mechanization grew, the Cavalry discontinued the breeding program in 1948 but the horses it created remained in local horse populations, especially in the Southwest. Hence their popularity in areas where movies and TV Westerns filmed. These were good Grade horses, something almost nobody breeds today, for good reasons. Shame
Clanter knows more about the Remount Service then I.
Anyway, hope that answers your question, just doing the job they were bred for and worked at most of their lives. Mind you, there were abuses here and in all facets of the horse industry, the good old days were anything but, much better today. It’s less likely with horses bred for the job and experienced at it handled by those who know what they are doing in any horse activity.
ETA because I know its going to come up if this thread lasts for long. American Humane first got involved with films in 1940 after industry insiders, including stars, stunt people and wranglers started speaking out. Their influence grew over the years to the point in 1960, production of many Westerns or efforts requiring many horses and stunts moved to other countries and thats why I wont watch a Spaghetti Western in particular and/or other period pieces with cringe worthy animal treatment.
The “No animals were harmed” disclaimer appeared in 1972 and the Screen Actors Guild negotiated for AHA reps on set from 1980 on. But not all films are union shops sooo viewers choice.