哺乳动物的乳汁成分和哺育方式Mammal Milk Composition and Mothering Styles

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这是一个鸡生蛋还是蛋生鸡的事情。

不同的哺乳动物生成的不同成分乳汁会影响它们作为这一物种的哺育方式吗？还是不同的哺育方式会影响物种自身生存所需的乳汁成分呢？

各种哺乳动物乳汁中的脂肪和蛋白质含量会依据物种的需要而产生相当大的差异。乳汁中脂肪含量最高的哺乳动物，需要让它们的幼仔迅速长出一层厚厚的脂肪来御寒。

灰海豹的乳汁中含有59.8%的脂肪，蓝鲸的乳汁中含有40.9%的脂肪。人类的乳汁中只含3.8%的脂肪。乳汁中蛋白质含量最高的哺乳动物，其幼仔生长得非常迅速，而且很快就会发育成熟。老鼠乳汁的蛋白质含量为12.9%，而人乳的为0.9%。

脂肪和蛋白质的含量与动物母子之间的关系也会互为影响。公共卫生医师及袋鼠式育儿法研究专家尼尔斯·伯格曼描述了四种不同类型的哺乳动物，以及它们的乳汁成分是如何与母子关系相关的。

藏匿型哺乳动物：幼仔刚出生时就相当成熟。母亲把幼仔藏在安全的地方，大约每12个小时回来一趟给它们哺乳。藏匿型哺乳动物的乳汁中，蛋白质和脂肪含量很高，因为必须让幼仔保持长时间的饱腹和安静状态。如果幼仔饿得哇哇大哭，就会更容易受到捕食者的攻击。鹿和兔子是藏匿型哺乳动物的典型代表。

巢穴型哺乳动物：巢穴型哺乳动物的幼仔出生时还不太成熟。它们一般生在窝里。出生后的早期，它们需要巢穴的温暖并和其它幼仔共处。巢穴型哺乳动物的母亲每隔2~4个小时回到巢中给幼仔们哺乳。这种哺乳动物的乳汁中，蛋白质和脂肪含量低于藏匿型哺乳动物。狗和猫是巢穴型哺乳动物的典型代表。

跟随型哺乳动物：这类动物的幼仔出生时已经比较成熟，在出生后很短的时间内就能很好地跟随妈妈。幼仔们日日夜夜都和母亲待在一起，频繁地吃奶。这种哺乳动物的乳汁中，脂肪和蛋白质的含量低于藏匿型或巢穴型哺乳动物。牛和长颈鹿属于跟随型哺乳动物的典型代表。

携带型哺乳动物：这类动物包括猿类以及有袋类动物，例如袋鼠。携带型哺乳动物出生时是最不成熟的。它们在很长一段时间内都需要被母亲一直携带着，并且要不分昼夜、频繁地哺喂低蛋白、低脂肪的乳汁。

人类是“携带型”哺乳动物。人乳是所有哺乳动物中脂肪和蛋白质含量最低的乳汁。这提醒了我们，人类婴儿从基因上就设定为他们需要被频繁哺乳、被经常抱着。

2022年8月更新

Mammal Milk Composition and Mothering Styles

This is a chicken and egg kind of story. Did the kind of milk produced by different mammals influence their mothering style as a species? Or did the mothering style influence the kind of milk needed to support the species?

The fat and protein composition of the milk of various mammals is quite different depending on the needs of the species. Mammals who produce the highest fat content milk need their babies to grow a thick coat of blubbervery quickly to protect them from the cold.

Gray Seals have 59.8% fat and Blue Whales have 40.9% fat in their milk. Human milk has 3.8% fat. Mammals whose milk has the highest protein content have young whose growth is very rapid and who will reach maturity very quickly. Mice have 12.9% protein compared to humans at 0.9%.

The fat and protein content also influences, or has been influenced by, the way the animal relates to its young. Nils Bergman, a public health physician and Kangaroo Mother Care researcher, describes four distinct types of mammals and how their milk composition relates to the relationship between mother and baby.

Cache mammals:The young are quite mature at birth. The mothers hide the babies in a safe place and return to feed them approximately every 12 hours. The milk of cache mammals is high in protein and fat because it has to keep the baby full and quiet for a long time. If the baby cried out in hunger, it would become more vulnerable to predators. Deer and rabbits are examples of cache mammals.

Nest mammals: The babies of nest mammals are less mature at birth. They are generally born in litters. They need the warmth of the nest location and the other young in their early days. The mothers of nest mammals return to the nest to feed every two to four hours. The milk of these mammals is lower in protein and fat than that of cache mammals. Dogs and cats are examples of nest mammals.

Follow mammals: The young of this group are also mature at birth and can walk well enough to follow their mothers within a very short time after being born. The babies stay close to their mothers and feed frequently throughout the day and night. The milk of these mammals is lower in fat and protein than that of cache or nest mammals. Cows and giraffes are examples of follow mammals.

Carry mammals:This group includes the apes as well as marsupials, such as the kangaroo. Carry mammals are the most immature at birth. They are carried constantly by the mother for an extended period of time and they are fed low protein/low fat milk frequently around the clock.

Humans are “carry” mammals. Human milk is amongst the lowest in both fat and protein levels of all mammals. This reminds us that human babies are genetically programmed to be fed often and carried a lot.

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Updated August 2022