Up to 1973, London Taxis were required to carry a bale of hay (for benefit of the long absent horse). https://www.ludlowthompson.com/property_news/searching-for-a...
https://www.legislation.gov.uk/ukpga/1831/22/pdfs/ukpga_1831...
I think its one of those cause and effect things.
You have a horse-drawn taxi. You wish to feed your horse at some point during the day.
The law says you can only do so with either (a) your own hay or (b) hay or corn held in your hands.
So the restrictions of the law push you in the obvious direction of keeping a stack of hay on your carriage.