All mammals (including horses) have a prefrontal cortex

The differences lay in functionality and composition.

The prefrontal cortex is the region of the brain that’s responsible for decision-making, problem-solving and social behaviour, and while the PFC (prefrontal cortex) is more developed in humans compared to other mammals, the size and complexity varies across species reflecting differences in cognitive capabilities.

One study investigates movement in feral groups of horses and how the PFC plays a role in the initiation of the movement by focussing on individual horses and the factors influencing these decisions.

Krueger, K., Flauger, B., Farmer, K., & Hemelrijk, C. (2014). Movement initiation in groups of feral horses. Applied Animal Behaviour Science, 158, 34-40. doi: 10.1016/j.applanim.2014.06.006

Sarah Schlote wrote an excellent article in her Equusoma blog in March this year citing references from as early as 1893, but even more interesting are her views around the misconception and why the myth has gained traction. She discusses anthropocentrism, human exceptionalism, diagnostic overshadowing and cognitive distortion.

Read the full article here https://equusoma.com/myth-busting-do-horses-have-a-frontal-lobe/