Thanks very much for this, especially the sources you mentioned, I will have to check those out.

I had no idea New Zealand was such a large agricultural exporter, but I suppose that makes sense the way you've described it.

And yeah, I had encountered some talk about the trouble with animal-based transport being limited by the need to bring food along or else have places you could reliably get it along the way. I'm also used to coming at this question in a military context, as supply lines and camp followers have always played a huge role in martial contexts. One book that I just realized assumes cheap transport for its recommendations is The Soldier's Load and the Mobility of a Nation by S.L.A. Marshall - he was all for having soldiers carry minimal gear, mostly fighting equipment, and then bring other needed supplies up by jeep. Hmm, I may have to look at it again sometime.