What is the carbon footprint of a horse compared to an automobile?

David Mason-Jones in an article in Hoofbeats states that a horse is a carbon “sink”. Interestingly, he states that “the biomass of a horse is a carbon sink in the same way as the biomass of a tree in a forest is a carbon ‘sink.’”
The digestive process of horses produces far less methane than the digestive system of cattle and sheep. Cattle, sheep, and certain other grazing animals are known as ruminants because their gut contains a rumen. …