eli5 Why do cows produce so much milk while pregnant? Instead of producing milk only after birth to feed their young? Does it have to do with the fact that they’re pregnant every year so their body is trying to produce milk for their previous offspring?
In: Biology
Yes, she’s making milk for this year’s calf while pregnant with next year’s.
In dairy production we dry off the cow (by not milking her) about 2 months before she is going to give birth. She needs a break from making milk to gain a little condition before she starts all over.
In beef production where the calves and cows are kept together, the calves will nurse as long as they can get away with it. Sometimes you will see last year’s calf try to get a nip in while the new calf is nursing!
Generally if you keep on taking milk the cow will continue to produce it.
BUT even though you could try and maintain a cow to continue producing a lot of milk, production tapers off anyway due to weather, hormones, feed, temperature, time of year.
The natural process is that as an animal is weaning then milk production slows down. By continually taking milk you effectively bypass the weaning part.
The whole process follows a yearly cycle :
Autumn – very low milk. drying cows off for wintering, impregnating for next season
Winter – cows growing calf inside them, sitting around doing nothing.
Spring – calves born, first milk, high quality feed produces high milk volume
Summer- continue to milk, milk volume tapering off, less good feed available.
They’re bred that way. The amount of milk dairy cows produce has increased over threefold since the middle of last century. A dairy cow can produce 30-50 liters per day, which is way more than the 4-5 liters a calf needs per day. We created cows that overproduce milk the same way we bread sheep that overproduce hair and turkeys that overproduce meat. Dairy cows have to be milked twice a day or they are in massive pain. Sheep need to be sheared once a year otherwise they disappear under their wool.
It’s purposeful selective breeding. Cattle is domesticated aurochs (the wild species is extinct now). Wild animals looked something like this [https://en.wikipedia.org/wiki/Aurochs#/media/File:Aurochsfeatures.jpg](https://en.wikipedia.org/wiki/Aurochs#/media/File:Aurochsfeatures.jpg)
Here’s a record breaking dairy cow [https://www.farmanddairy.com/news/holstein-cow-sets-national-milk-record-of-77480-pounds/392855.html](https://www.farmanddairy.com/news/holstein-cow-sets-national-milk-record-of-77480-pounds/392855.html)
As you can see, the size of the udder is very much not a natural feature.
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