My story has a species of civilized creatures who feed singularly on blood. They can harvest it from livestock (likely cattle) and keep it stocked (they don’t need to drink directly from the animal).

From what I can tell, there are two ways for them to harvest blood: either slaughtering livestock at a certain age and draining their blood, or “milking” the livestock by taking repeated, controlled doses from adult livestock (before likely slaughtering the animal at old age). Which one of these options makes more economical sense?

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    $\begingroup$ Is there any reason can't do both? Here, we're looking for social, cultural, religious or historical reasons. As for economics, can you describe the general economy for us? Also, are their cattle sentient? $\endgroup$
    – elemtilas
    Commented Apr 26 at 0:22
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    $\begingroup$ More information needed - are the bloodsuckers controlling all cattle throughout the breeding cycle or are they buying/capturing cattle from elsewhere? How reliably can they take an involuntary blood donation without causing an infection that will make the creature's blood unusable in future (% chance)? Can they use all of the blood from an animal reliably when it is slaughtered or is there too much and a lack of preservation technology? Economics is about numbers, which are not provided. $\endgroup$ Commented Apr 26 at 4:00
  • $\begingroup$ Beware when you bring economy to the table, because of capitalism. An animal might be able to give out hundreds of liters of blood during the course of its life, but if the blood of a cub is more valuable to sell than that of an adult, many will be slaughtered early to maximize profits. $\endgroup$ Commented Apr 26 at 5:53
  • $\begingroup$ Keeping them for many generations will probably also result in the bloodlines that can reliably give the most blood the most easily being favored, creating a variety of livestock that is selectively bred for blood production, rather than meat or milk. Like, Holstein cows produce far more milk than their calf would ever need. The feed would go more into blood production and less into meat, etc than with our domestic livestock today. $\endgroup$ Commented Apr 26 at 21:08
  • $\begingroup$ there are human societies that bleed cattle rather than slaughtering them. look up the Maasai $\endgroup$
    – John
    Commented Apr 30 at 20:55

4 Answers 4


First thing you need to calculate how much blood a bloodsucker would need to drink to survive.

Blood has 700 calories per liter. Assuming your Bloodsucker is human-ish, they would need around 3 liters per day to function properly and about 5 liters per day if they need to do any kind of hard work. Super hard work, like traditional farming, mining, fighting in battles: probably 7+ liters per day.

A big cow has about 30-40 liters of blood in it. Bloodletting it for 3 liters, every 2-3 weeks should be fine. 5 liters every now an then, but letting the cow rest and recuperate longer, sure. Anything more than that, and the cow will become weak, anemic and easily die of some otherwise preventable sickness.

So, I would guess that you would need about 15 cows per Bloodsucker to make the system of bloodletting even possible, or preferably closer to 20 to have a safety margin. Bloodletting other livestock, like goats, sheep, pigs etc is also possible, but would not matter much.

Slaughtering for blood would need 3 cows a month killed to support one Bloocsucker, preferably 6 cows to have a safety margin. I do not think this is economically sustainable, cows do not breed that fast.

Verdict: Bloodletting of 20 cows a month per Bloodsucker, in 15 day intervals, plus the occasional slaughter of older cows and non-bovine livestock.

One possible "out of the box" solution would be to either breed very large creatures in semi-captivity (elephants, whales, very big fish like tuna) and bleed them for sustainable efficiency as they graze, or farm spectacular numbers of small, fast breeding creatures and slaughter them (ie: breed billions of bunnies, funnel them into a giant blender, sieve the chunks, drain blood out.)

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    $\begingroup$ That last part about the blender makes me think of that being the "lowbrow" or low-cost industrial food source for the society, and higher-class or more well-off folks get the cow blood that's free of non-blood fluids and microscopic chunks. $\endgroup$
    – ke4ukz
    Commented Apr 26 at 21:44

Without casting aspersions on them - you could look at the Maasai tribe in Africa.

They have some food/drink combos that involve drawing the blood from their cows. They also slaughter their cows.

Also - as the commentor noted - there is no reason why a civilized society wouldn't do both - regular blood 'donations' (just like if you or I go to give Blood) but at a certain age, the stress of loosing a pint of blood is too much - at which point the Animal would be slaughtered and drained of all blood.

A Civilized race (if there are other trading races) would then ensure that the Meat from the slaughter wasn't wasted.

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    $\begingroup$ Interesting point that the meat would wind up primarily being a trade resource! One other point of note, though,is that if this species domesticates any carnivores/omnivores the "blood byproduct" meat could be used as feed for those domesticated animals. $\endgroup$ Commented Apr 29 at 12:00

"Milking" Would be the Standard

While they'd no doubt slaughter older or injured "milk" animals and have some species that they'd eat "raw" or kill then drain, periodic bloodletting would absolutely be the norm for their mainstay farmed food animals. If they've been at domestication of food animals for as long as humans have been (8,000-11,000 years) then they'll undoubtedly have bred their animals for blooding. Which means that unlike humans, who breed for size and meat quantity, your vampires would be breeding for blood replenishment and hardiness.

Your "cows" would be selected to give more blood per letting (say 4-5 liters in a 40-50 liter animal, or enough to feed a working adult for the day) and/or allow for more frequent bloodletting. Either way their immune systems would be miles ahead of our farm animals. Sheep/cows/pigs/chickens are notorious for their propensity towards illness if injured. Since Vamp farm animals would be "injured" essentially nonstop to allow for bleeding they'd bred to be far more robust than human food animals.

My instinct says they'd farm as large an animal as possible (think hippo/elephant compared to cattle/sheep) since unlike humans they wouldn't worry about having to kill the thing every time they needed to eat. Plus a larger animal can afford to lose more blood per blooding. They'd likely have very visible and large veins as well to aid with the bloodletting process, though I'm not sure if it'd be better for them to have blood that coagulates quicker (swifter recovery, harder to store for your vamps) or slower (steadier flow, easier to store, but easier to lose lots of blood due to injury).

It's also likely that your primary food animals would give some other renewable product like wool. For humans, who kill the animal, things like usable hide/horns/sinew are or were big factors in selecting farm animals. For your guys since they want their farm animals alive having something they can harvest from the animal that doesn't kill it would make farming said animal much more profitable.


No fruit you can buy today- is natural. We bred them into existence. Domesticated blood milking would result in similar deformations to the domesticated creatures.

Given the deformation of characteristics through breeding in lifestock, you would get a creature pretty fast that are basically just eating to support enormous spleens, bones and thus marrow, generating blood faster then it can be extracted, all else that needs energy would dwindle (higher brain functions, muscle tissue). The coagulation factor would drop to allow faster extraction.

Or even horrific- there are host creatures- and a blood cell producing cancer, that is just grafted onto them. It grows, it spreads, the harvest is bountiful, the creature itself suffering enormously, but hey - thats okay.

The final stage would be DNA-transfer from this cancer to a plant and you get bloody-grape-fruit, with actual blood. Yummy. Vegetarian Vampires, it can be done!


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