Milk: The secrets of the dairy

In this supposedly health conscious age, for a nation shy of breastfeeding our human babies it is perhaps ironic that for many adults and children a 'daily dose of health' comprises of fermented bovine mammary gland secretions with added microbes, perhaps fruit, and sugar.

Marketing might convince people to buy things but it rarely educates them about what they are consuming or where it has come from, and often just serves to confuse.

Heroic effort in the dairy shed

I'd like to see a pot label that acknowledges the heroic metabolic efforts of the average dairy cow to produce all the milk that goes into yoghurt production.

Most people will be aware that cows need to produce calves to trigger lactation. But visualise, if you can, up to 10,000 one litre milk containers stacked up high and wide – that's how busy your average high yielding dairy cow is over the course of one, approximately 305 day lactation period (just short of a year).

To accomplish this feat she needs to consume over 7 tonnes of food, chew everything twice (ruminate) and drink even more water. It's no wonder that the cow has been described as an appendage to her mammary glands.

One cow, thanks to selective breeding, can produce more than enough milk to feed one (occasionally two) calves and a whole herd of milk and yoghurt consuming humans!

If that's not impressive enough, consider that a cow's gestation period is approximately 9 months - very similar to humans - so for the majority of the time that she is producing and being milked, she is also pregnant with her next calf. That's assuming, of course, that she has managed to divert enough energy to be able to conceive successfully.

Milk production is driven by the cow's own secretion of growth hormone. How she partitions nutrients between producing milk secretions and other essential bodily processes then determines whether the cow is able to conceive (mostly via artificial insemination) and maintain another pregnancy, to start the whole cycle off again.

Milk contains water, nutrients (fat, protein, sugar in the form of lactose, vitamins, minerals), immune system cells and also biological growth factors that influence gastrointestinal tract (gut) development.

Humans (and some of their pets) are the only animals that continue to consume milk or milk products in significant quantities beyond juvenile stages (and also, uniquely, from species of mammals different to their own).

Why do mammals produce milk anyway?

Other than whether milk is actually suitable for older animals, there are questions still remain surrounding the evolutionary pressures that led to the formation of mammary glands and their secretions.

Most people assume that the biological purpose of milk is as a food - but that might not have been the primary driving force. Some scientific theories suggest that mammalian milk evolved mainly to provide immune protection in naïve young.

The downside of drinking milk

Whatever the evolutionary pressures that resulted in mammalian milk, its consumption is undoubtedly tailored for young animals. Whilst there may be some immune and nutritional benefits to consuming milk beyond childhood, one should always consider the possibility that there may also be unintended consequences.

Individuals with lactose intolerance have lost the ability to produce the enzymes that digest the lactose in milk. As this can result in unpleasant side-effects, they generally stop consuming dairy products.

Food for thought

Food for thought: when you next buy (and consume) the yoghurt dream, ponder the reality of how the contents of your yoghurt pot came about.

If you are eager to learn more about nutrition, how your body makes use of food and how food is produced from natural resources, there are plenty of Open University life sciences courses available to tickle your knowledge-seeking tastebuds…