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So as most of you probably know, cows don't produce milk all year round for no reason, they need to be pregnant and then you gotta do something with the calves…

Now in my story that has an ecosystem pretty much based on what you would find in the late Eocene on Earth, I was hoping to have some kind of milk-producing domesticated animal.

Now my question is: would it be possible, through evolution/voluntary selection during domestication, to make it so a mammal would produce milk all the time without needing to be impregnated every year or so?

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    $\begingroup$ Breeding a milk cow every year is not required, although it appears to be common practice. From theprairiehomestead.com/2014/03/family-milk-cow.html : "DO YOU HAVE TO BREED A COW TO GET MILK? Yes–in order for a cow to produce milk, it needs to have a baby first. Most cow owners breed their cow every single year so they have a fresh lactation cycle. However, you don’t have to do this. As long as you continue to milk, a cow can go for several years on one lactation cycle. But they must have a calf initially to get the lactation going." $\endgroup$ – bitchaser Sep 28 at 19:45
  • $\begingroup$ If true, this should be an answer. And it should be the top voted answer because it answers the question. $\endgroup$ – Daron Sep 29 at 0:25
  • $\begingroup$ @Daron it is already included in two separate answers. $\endgroup$ – John Sep 29 at 14:47
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    $\begingroup$ Have a look at the yield graph of a lactating cow. It goes up rapidly to a peak and then tapers off in a linear fashion. After about 9 months you're getting less food value in milk than the cow is eating to produce the milk and maintain herself. Retired farmer. $\endgroup$ – Victor Paine Sep 29 at 16:20
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    $\begingroup$ Just for reference, I grew up on a small farm that had two, maybe three cows at any one time that produced milk. It was literally years between them calving, so the cow doesn't have to be pregnant. Mind you, there's a significant difference between cows used to produce milk for a family and cows on a dairy farm. $\endgroup$ – Keith Morrison Sep 30 at 16:43
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Producing milk takes energy.

Gathering energy from food is never easy in nature, so every organism will be wise in spending it. Therefore no organism is going to naturally produce a steady flow of milk if it doesn't serve some purpose which can have a higher return on investment.

The only way to have this forced via selective breeding would be to have some pathological condition, in which a cow or other animal produces milk continuously and to select for a breed which has this pathology as a genetic trait, or alternatively to find a way to induce this pathology at will.

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    $\begingroup$ we already induce lactation in cows using hormone injection. the main limitation is cost. ncbi.nlm.nih.gov/pubmed/15377608 $\endgroup$ – John Sep 28 at 2:25
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    $\begingroup$ I am talking about a bronze age people, though, so hormones is not an option. $\endgroup$ – Nierninwa Sep 28 at 17:25
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    $\begingroup$ @Nierninwa: Pants produce many hormones or hormone-like chemicals. Just have your people discover that feeding your animals a bit of "milkweed" keeps them producing milk. $\endgroup$ – jamesqf Sep 29 at 4:11
  • $\begingroup$ @jamesqf - the milkweed would have to be introduced to the area or otherwise normally unavailable, or the animals would have evolved some kind of defense for its effects (even if it is, don't eat them). The cost of eating milkweed would be enough, in spilled calories and unnecessary milk production processes, that those animals who found the milkweed would be strongly selected against in the wild. It makes more sense if the milkweed is not native to the area, or ridiculously rare, maybe cultivated for some other reason before its milk production effect was known... perhaps to produce pants :) $\endgroup$ – Megha Oct 6 at 6:57
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Yes. You are such an animal.

Human females will make milk for as long as milk is withdrawn from the breasts. At the farmers market 2 weeks ago I bought jam from a woman who appeared to be nursing a 3 year old. Back in the old days, a woman hired as a wet nurse could successively nurse child after child.

https://en.wikipedia.org/wiki/Wet_nurse

Dr Gabrielle Palmer[8] states: There is no medical reason why women should not lactate indefinitely or feed more than one child simultaneously (known as 'tandem feeding')... some women could theoretically be able to feed up to five babies.

It is an excellent adaptation for a social animal such as ourselves - if a mother dies or is too sick to nurse, or is simply not available, other women in her social group can nurse the child.

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    $\begingroup$ IIRC even men can be induced to lactate by sufficiently strong suctioning being applied to the nipples on a regular basis. $\endgroup$ – nick012000 Sep 28 at 5:19
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    $\begingroup$ @StarfishPrime The first time I heard about men breastfeeding their child is from the early 2000s of a villager (don't remember where, probably South Pacific) whose wife passed away - in that case it was just necessity - he couldn't afford to buy milk, no external input of hormones etc. $\endgroup$ – slebetman Sep 28 at 16:55
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    $\begingroup$ @slebetman yes, that's why I clearly said "some men". Most cannot, in the absense of hormone imbalances caused by illness or starvation, because men don't generally have a whole lot of prolactin in their bodies. This is why male lactation is rare. Put it this way, if it were common, or even merely unusual instead of vanishingly rare, there would be a lot more porn of it ;-) $\endgroup$ – Starfish Prime Sep 28 at 17:38
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    $\begingroup$ @Nierninwa that is less being milked every day, than producing several TIMES as much milk as they naturally would. keep in mind modern dairy cows produce 3-4 times as much milk as their ancestors. if your body is producing anything at 3-4 times what it originally evolved to produce it will be a strain. $\endgroup$ – John Sep 29 at 0:56
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    $\begingroup$ @ChrisH - where else would they get their iron from? (also, pretty interesting reading :) $\endgroup$ – Megha Oct 6 at 7:08
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You could give them a mechanism like some goats. Something that occasionally occurs in goats is once they have given birth once they will keep producing milk for their entire lives as long as they are milked every day. This is not unique to goats and pops up in several mammal groups, especially social species. If they are not milked for a few days they quickly stop producing, but this means you can keep milking them for the rest of their lives as long as you, well, keep milking them.

Really you are chasing a non-issue however, most of the time you eat the old ones and raise the newborns into productive livestock. keep in mind you are talking about a year or more between births and cows for instance can be impregnated at 13 months old. You are going th be eating most of the male offspring anyway, since they will not be producing milk.

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  • $\begingroup$ I mean I was hoping for something that allows to bypass that so that you have a single animal and whenever you need milk it is producing some whether or not you milked it daily (which is quite a strain on the animal). $\endgroup$ – Nierninwa Sep 28 at 17:27
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    $\begingroup$ That is never going to happen naturally, milk has to be produced before milking so it would be the same stress regardless, it would be producing milk every day and just leaking it on the ground, that is just as costly to the animal but also has a high risk of infection. $\endgroup$ – John Sep 28 at 18:34
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    $\begingroup$ I get you want the animal to be available for milking at a moment's notice. But I don't see why you wouldn't be milking it daily anyway. Rememeber your bronze age people have no way to preserve the milk so even if the cow produces 4 gallon of milk today we cannot save it up for two says to avoid milking the animal tomorrow. $\endgroup$ – Daron Sep 29 at 0:31
  • $\begingroup$ Also consider whether the strain on the animal is through daily milking (the mother would suckle her young every day of course!) or through producing ENOUGH milk to feed 100kg calf. $\endgroup$ – Daron Sep 29 at 0:33
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    $\begingroup$ @Nierninwa milk is not produced during milking it is produced long before milking, so to be ready to milk at a moments notice it has to be producing the same amount of milk as if it was being milked. the strain is the same whether milk is collected or not. $\endgroup$ – John Sep 29 at 1:01

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