Are domestic cattle truly smaller than the aurochs?

The question in the headline of this post will immediately be answered with “yes, obviously” by most people, which is understandable as the European aurochs is known for being a very large bovine and the size reduction is one of the most noticeable consequences of domestication in cattle. However, there is one aspect that should be considered. 

It starts with how to define body size. In mammals, one of the most widely used parameter of body size is the withers height. Going by this factor, it is obvious that the aurochs was much larger than most domestic cattle – very large breeds like Chianina or Bhagnari being the exception. Go here for my post on how large the largest aurochs might have been.

When naming the largest living land animal, most people will say it is the African elephant. This is because it is the heaviest terrestrial animal. But going by height, it would be giraffes, and going by length, the reticulated python would be the second-largest terrestrial animal on earth. Yet, those species are rarely considered the largest terrestrial animals. So, is mass the most important body size parameter? It is certainly an objective one, as it is almost independent of the morphology and bauplan of the animals (with the exception of birds which have an air sac system and pneumatized bones, which is why their bodies have a lower density than those of other terrestrial animals). If we go only by mass, let’s examinate if cattle are truly smaller than aurochs. 

One problem is that we do not know the exact weight of aurochs. No aurochs were weighted, so we can only guess by using extant wild bovines as a comparison. Since the males are larger than the females in bovines, I only refer to the mass of males in this post. Perhaps the weight of the aurochs was somewhere in the range of banteng, wisent and wild yaks, which would be between 700 and 1000 kg. Wild yaks have a slightly more elongated and more robust morphology than the aurochs had, but have a similar height compared to the largest aurochs (which is roughly 2 metres) and their weight is around 1000 kg. While yaks are built slightly more massive than aurochs, they have a higher shoulder hump, what influences the withers height. So it could in sum be that a 200 cm tall aurochs was roughly the same weight as a 200 cm wild yak. That would mean that a 160 cm aurochs had only about 510 kg. The wisent has similar proportions and a roughly similar build. The record for wisent height is 188 cm, for the weight it is 840 kg in wild-living animals. That means a 2 m wisent would be 1011 kg and a 160 cm wisent would be around 500 kg. Banteng reach up to 190 cm and 900 kg weight, which would be 529 kg in a 160 cm banteng. Since all those three bovines result in a similar weight range, maybe it is reasonable to assume a weight of around 500 kg for a 160 cm aurochs, and 1000 kg and slightly above for a 200 cm aurochs. Keep in mind that weight increases with x³ while height only with x. Those are only very rough estimates, and the weight would also depend on the individual condition of the animal and the season. 

What is interesting now is that many domestic bulls surpass the possible weight of the largest aurochs. Bulls with a weight of over 1000kg are actually not a rarity in breeds of a medium height. For comparison, the Taurus bull Lucio had a withers height of 165 cm and a weight of 1400 kg. A 165 cm tall aurochs bull would, if the estimation above is correct, weigh around 500 kg. So the Taurus bull has more than twice the mass of an aurochs with the same height. That is due to the different morphology: domestic cattle mostly have shorter legs and a longer trunk, plus a smaller hump as much as a way bulkier trunk, especially the intestines are enlarged. This results in a higher weight relative to the withers height.  

Lucio the Taurus bull (Sayaguesa x Heck)

The morphology of cattle drastically changed during domestication: the legs became shorter, the trunk longer, the intestines larger, the head smaller, the hump smaller et cetera. This led to a dramatic height decrease, while the mass was not that much affected. Surely there are dwarf cattle breeds that are lighter in weight than the aurochs probably was, especially during the Bronze age there were tiny cattle that were about the size of a sheep. But as far as the average modern day cattle body size is concerned, cattle lost height during domestication but not necessarily mass. In some cases, mass was even gained compared to the aurochs. 

So, if mass would be the only parameter for body size, then most domestic cattle are not necessarily smaller than the aurochs, it is their morphology that changed dramatically.