What is the breast milk with the highest amount of fat in the entire animal kingdom?

The lactation defines mammals as a class within the animal kingdom. It is one of the most powerful phenomena of nature that exist, during which a relationship is generated between the mother and the offspring that goes far beyond the simple emotional bond.

All mammals produce leche, from the monotremes, those that have a beak and a cloaca, to the marsupials, such as the kangaroo, passing through the placentals, among which we find ourselves. We all descend from a common ancestor who lived in the Triassic, more than 150 million years ago.

Milk of seals and whales

Behind the part it is essential that the offspring of mammals receive both colostrum and mother’s milk. The main difference between the two lies in its composition, while colostrum is rich in vitamins, sodium, calcium, iron and immunoglobulins, milk has a higher lactose content.

As the time of lactation passes, the composition of the milk varies, it adapts to the new needs of the offspring, in this way the percentage of lactose decreases and the percentage of proteins and fat increases.

The differences in the composition of milk between mammals is enormous. Thus, the milk of the hooded seal has 60% fat, being the mother’s milk with the highest amount of fat in the entire animal kingdom. It is followed, in terms of fat composition, by whale milk, which has between 30 and 40%. At the other end of the scale are black rhinos, whose breast milk contains only 0.2% fat.

Human milk is quite different from the milk of these mammals as it contains 4% fat, 1.3% protein and 7.2% lactose, a composition that closely resembles that of zebras.

A biology full of singularities

Seals belong to the group of pinnipeds, like sea lions, and have four fin-shaped limbs, the two rear ones being fused into one. Unlike the sea lions, the ears of the seals do not have an ear pinna.

Their biology and behavior are riddled with singularities, from the fact that they don’t chew food to that they don’t drink water or that they have a muscle inside their nostrils that closes their orifices at the precise moment of submerging.

Typically these mammals have between 40 and 50 ‘whiskers’ or vibrissae on both sides of the nostrils with which they capture the fluctuations of the water through more than 1,500 nerve cells, a very high figure if we compare it, for example, with the 100 or 200 cats have.

Regarding reproduction, their sexual maturity varies between two and seven years of life, depending on the species and sex of the animal, and they have an evolutionary strategy known as delayed implantation or embryonic diapause. It basically consists of the fact that the fertilized egg does not implant immediately in the uterus as it happens in Homo sapiens, but it can be delayed for weeks. It is a strategy of nature with which the risk of childbirth or lactation occurring in unfavorable situations that could endanger both the life of the mother and that of the offspring is avoided.

The gestation of the seals varies between 9 and 11 months and the birth occurs on dry land. There the calf is born -usually one- with a weight of around 4.5 kilograms. The breeding areas chosen by the mothers are sandy beaches, rocky ledges, ice floes or sandbanks. While lactation lasts, the mother does not separate from the calf and suppresses its intake, which is why lactation has to be brief -between 30 and 45 days- and the milk has to have a high fat composition so that the calf can develop quickly.


Peter Choker

He is an internist at El Escorial Hospital (Madrid) and the author of several popular books.


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