Is it true that only pregnant cows produce milk?

There is an opinion that in order to produce milk, cows must be pregnant all the time. We decided to check if this is true. 

The statement that cows produce milk only during pregnancy can be found in educational literature. websites about animals. InterestedIs that so, visitors? services questions and answers. Posts with such headings are found on blogging platforms (for example, on “Zene"). Users social networks say they were surprised to learn that “cows only give milk if they are pregnant, not just because they are cows.”

Milk in cows, like in other mammals, intended to feed their young, so cows don't really give milk simply by virtue of being cows. Female calves do not produce milk; to do so, they need to reach puberty (at about 15 months), and then become pregnant (that is, pregnant) so that their mammary glands fully develop. 

However, before the first calving, the cow, even when pregnant, does not produce milk. Moreover, for several days immediately after birth, her mammary glands produce not milk, but the so-called colostrum - a liquid containing a large number of antibodies to various bacteria and viruses and designed to develop passive immunity in the calf (that is, not acquired as a result of an infection). In addition, unlike milk, colostrum contains contained a greater amount of vitamins, minerals, growth hormones and other substances necessary for the baby in the first days of life. This substance is useful, but unsuitable for mass production, since due to its composition it is poorly susceptible to pasteurization and therefore can be stored for a very short time.

The physiology of mammalian lactation in general does not provide for the mechanism of milk secretion during pregnancy: during this period, the hormones estrogen and progesterone block release of prolactin (the hormone responsible for lactation) from the pituitary gland, and also make breast cells immune to it. After childbirth, the hormonal “blockade” is removed due to the release of the placenta along with the fetus and a decrease in the activity of the ovaries. After calving, the cow can produce milk within ten months, by the end of this period its quantity naturally decreases. New lactation in animals begins only after the next birth.

Pregnancy in cows, like in humans, lasts about nine months. Since farmers strive to get as much milk as possible, and the dairy cow’s body as a whole ready by the next calving already 12–14 months after the previous birth, animals are usually fertilized again without waiting for the end of the lactation period. In this case, cows can still produce milk during pregnancy, and in factory farming they do give birth for almost the entire part of their lives when they can produce milk (which is about three to four years). As for beef breeds of cows or animals kept on small private farms, whose owners are not interested in almost year-round milking opportunities, their periods of lactation and pregnancy usually do not overlap. 

Thus, without becoming pregnant and giving birth to a calf, cows really cannot produce milk. During pregnancy itself, it, like in other mammals, is not secreted, since this process is blocked by hormones. A pregnant cow can only produce milk if she was impregnated while the previous lactation was still ongoing (and this is usually the case on commercial farms). However, a calving cow does not need to become pregnant again to produce milk for ten months after giving birth, as it will be produced naturally. But if the owner of a cow wants her to continue to produce milk with minimal interruption, then the cow should calve and give birth every 12-14 months - but this mainly applies to industrial animal husbandry.

Cover photo: pexels.com

Mostly not true

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