"Then I reject your reality and substitute my own!" shouted Dr.[Redacted].
So, I wanted to have a more vintage feeling to cities in my setting, despite being around the technological levels of the 21st century. One of my ways to achieve that was to separate civilian methods of transportation into three main categories:
- Between cities, people use cheap and fast maglev trains.
- Sub-Atm underground "bullets" are used to transport materials and products. You can't use it to transport living creatures, though. These subterranean maglev pipes that have pressures of less than one atmosphere, though usually, it's not zero.
- Horses and horse carriages are used to travel inside cities and on difficult terrains. I mean, there are only a few dragons and dragon riders, the rest of the park rangers will have to settle for an ass.
Now, these aren't just regular horses, but a special, genetically altered group of breeds, collectively referred to as D-Horses, which were the legacy of Dr.[Redacted].
City horses are smaller, around 145-150 cm at the shoulder. In winter, they grow fluffy coats to keep them warm. City horses are naturally capable of extra gaits that are pretty useful. They're also harder to spook, potty-trained, capable of understanding color-coded roadsigns and that they have to avoid trampling or running people over. Usually, they're more responsible than their drivers.
All-in-all they sound pretty good for short-distance travel. However, another key ingredient of making them more useful than cars is that D-Horses are way less susceptible to food poisoning than their non-altered cousins and can eat all kinds of plant matter and even eggshells. They still require some diversity in diet, but not as much as a horse. Since they're potty trained, we know their digestive system was altered, but I'm not sure how it should work.
Just a side note that guts also act as a kinda-sorta piston, helping push air out of the creature's lungs when running.
So, how should the D-Horses' digestive system maximalize its efficiency, as in extracting as much energy and usable material from food as feasible for the least amount of work?