a little exercise in critical thinking

Grant‘s just sent me a piece that a recent Sciblog commenter posted on a US website. (Oh, all right, it was the Huffington Post. Not a place to go for good science coverage, but anyway…)

I knew a New Zealand dairy farmer who told me that her 9-year-old daughter had been growing breasts and pubic hair. Somewhat alarmed, she and her husband tried to figure out what caused the problem. It turned out that the vet had injected a few cows in ther herd which had not become pregnant in the first round of artificial insemination with a powerful hormone to induce ovulation, in the hope to impregnate them this time. The milk from these cows, along with the milk from all the pregnant cows, had been going into the tank from which the milk was collected by a milk tanker in the morning. The family had used some milk from the tank for their daughter’s breakfast every morning. Once they realised what the problem was, they stopped using the milk and their daughter reverted back to normal. So much for "100% Pure New Zealand"!


Let’s just sit back & have a look at the many misconceptions that this piece contains 🙂

Quite by coincidence there was a piece in the newspaper just a few days ago (similar to this one) about the lowering in the age at which children begin to enter puberty, over the last few decades, to the point that for many girls the related physical changes begin from about 9&1/2 years of age. The on-line encyclopaedia Te Ara tells us that "[in] 2000 puberty occurred three years earlier on average than it did in most western societies a century earlier – probably largely because of improved nutrition." (Now, this brings with it a number of attendant problems – not least, the need to look at the sort of s*x education children receive and when they receive it; however, that’s not something I want to get into at this point.) More recently, it’s possible that increasing levels of obesity have an impact, because body fat is a source of oestrogen. (See work by Sir Peter Gluckman, for example.) And some people have also raised concerns about the amount of oestrogen and other related hormones in the environment. So it’s not completely unlikely that this apocryphal farmer’s daughter might have been entering puberty as part of the normal run of things, and that the milk she was drinking had nothing to do with it. Correlation does not equal causation.

Since dairy farmers need their cows to be pregnant and subsequently lactating, injecting hormones that induce ovulation (such as luteinising and follicle-stimulating hormones) into cows that haven’t become pregnant is a common management practice, and there’s a reasonable amount of literature on the best way to manage this (here, for example). But the hormone treatment (& the vet’s time) is going to cost money, so that it’s extremely unlikely that the family described by the HuffPo’s correspondent would be unaware that the vet had treated some of their herd in this way. Good herd managers are going to be very much aware of what’s going on with their cattle.

The other thing is, these hormones don’t last indefinitely in the body. They’re produced (injected), initiate changes, and disappear: the half-life of luteinising hormone in the human body, for example is around a couple of hours. So because the treated cows are not going to be continually expressing these hormones in their milk, it’s hard to see how this child would have been receiving a regular titre in the milk on her breakfast cereal. And if she was, then in all probability so was the rest of the family – was no-one else affected? Plus there’s the matter of dilution factors, as the milk from the few treated cows would be considerably diluted by admixture with the milk from the rest of the herd. And the principles of homeopathy apply here about as much as they do anywhere else i.e. not at all 🙂

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