This week I was asked to weigh in on an issue that was brought up by a Mom and Partner Family in JP about estrogen in milk. Since I knew very little about it I thought I would toss the question at Amy Huyffer of Strafford Organic Creamery. As seems the case with thoughtful and experienced people like Amy, there are far more questions than answers – and it seems as usual that the press is quick to draw sensational conclusions rather than leave us in a mode of curiosity and inquiry.
Here is her response:
I don’t know the levels of estrogen in our cows’ milk, so I did what your customers likely do when they have questions about stuff like this, I googled it. And from what i can tell, most of the articles seem to refer back to a 2006 study published in the Harvard Gazette, http://news.harvard.edu/gazette/2006/12.07/11-dairy.html, that found that cows in the late stages of pregnancy can have up to 33 times the level of estrogen as non-pregnant cows. The researching scientist was from Mongolia and the results of the study were based on some comparisons between Mongolian raw milk and homogenized “modern” milk, from the U.S. or Japan.
I don’t know what to do with that. Hormone levels in milk rise as a cow progressed in her pregnancy. And it’s certainly true that we milk our cows while they’re pregnant. They don’t say what they’re calling “late stages of pregnancy,” though. Our cows are generally dry for the last 80 days of their pregnancy. Industry standard is 60 days dry.
Google also produces articles with differing thoughts on whether the hormones are broken down by digestion and whether homogenization is a factor. (These are blog entries and don’t cite their sources.) The Harvard study tested only homogenized whole milk, skim milk and Mongolian raw milk. The American skim and Mongolian milk had very low hormone levels, which makes sense because hormones hang out in fat and Mongolians only milk their cows for five months of the year (likely dictated by climate–you need to have dense feed available to keep the cows close enough to call them in to milk). They tested organic and conventional homogenized whole milk but didn’t say if there was any difference between them, and they didn’t test unhomogenized milk.
American skim milk and Mongolian raw milk, the Harvard study found, had very low estrogen levels, which makes sense because hormones hang out in butterfat, as do vitamins and CLA, an anti-carcinogen.
What I can tell you is that we are milking a lot of un-pregnant cows and that most of our milk comes from cows who are not in the later stages of pregnancy. This is not based on hormone research, but because cows give the most milk right after their calves are born and then start to taper off when they become pregnant. A cow that might give 65 or 70 lbs. per day in the months after she has a calf will be giving maybe 10 0r 12 when we dry her off. We also have a lot of cows who don’t breed back right away and we keep them around for a long time, hoping they will. This is because we’re softies. Sweet Pea, our best producing cow, has been milking for 260 days and isn’t pregnant. Buerre, also a great producer, has been milking for 388 days and is maybe 30 days pregnant–too soon to tell. We aim to have our cows bred at 90 days postpartum, but that doesn’t always work out and we take what we get.
I’m sorry I don’t have a better answer. I can’t find any good science. It seems to me that health and diet articles sell themselves by making lists of good and bad foods and that milk doesn’t fit into that kind of characterization. As the Harvard researcher said, “Milk is complicated.”
I’m glad people are interested in this sort of thing, which will hopefully drive better studies. We always want to know what people are thinking and how we might factor that in as we move our farm forward.
Thanks for the opportunity, however poorly I have used it, to respond.
All the best,