That's a very good point. I'm currently suspecting that the numbers quoted in Blakewell's article are the "hot carcass" weight (i.e. subtracting bone, head, and organs from the total weight). An Aurochs (wild ancestor of domesticated cattle) could reach 1300 lbs in the 1500s (and possibly in excess of 3300 lbs prior to recorded history, according to archaeological finds)[0].

If the numbers are hot-carcass weight, we would be seeing:

1700: 370 lbs, 1789: 840 lbs, 2020: 880 lbs [1]

But, uhh, that doesn't feel right either. I think that wikipedia page could use some additional citations, but I'm struggling to find useful numbers with which to update.

[0] https://en.wikipedia.org/wiki/Aurochs

[1] https://beef.unl.edu/beefwatch/2020/how-many-pounds-meat-can...

Domestic animals in the Middle Ages were definitely smaller than today, you can see it in illustrations that depict agricultural work.

For people who lived in swampy areas (e.g. north of England), having lighter animals with longer legs was actually preferrable. Meat-and-fat balls of today would get stuck and drown in mires.