Quote:
Originally Posted by Subby
I googled this and the very first article that came up was a news item from the Harvard Gazette.
Hormones in milk can be dangerous
Cows are milked up to 300 times per year and are often pregnant while being milked. The farther along into pregnancy a cow is, the higher its estrogen levels are, and this is passed along through the milk. We get 60-80% of our estrogen from dairy sources.
Pregnant cows produce up to 33x more estrogen than non-pregnant cows.
The takeaway is that - even if lungs is right and cows are not being pumped full of estrogen, they still produce enough in their own right to have some cause for concern. |
The original claim that we pump our cows full of estrogen was probably mistaking estrogen for somatotropin supplementation. Completely different things, and the only link between somatotropin and estrogen is that supplemented cows will have slightly elevated levels of estradiol at the stage of estrous where estradiol increases (this takes place on a single day).
Just paging through the
Endocrinology of Pregnancy and while I don't have any clear cut numbers, it states that estrogen levels in pregnant cattle are low through most of the pregnancy but near-term is where estrogen levels peak. Standard practice is to not milk cows in the last 60 days of pregnancy to allow the cows' mammary tissue to regenerate. I'll try to dig around for more concrete information from scientific sources. But from what I do know at this point, we do not harvest milk from cows at peak levels of estrogen production.
The article is also a bit misleading about milking of pregnant cows. While it is correct that we do milk lots of pregnant cows (it's not economical or healthy to the cow to feed her for 9 months while not milking), they really don't quantify the proportion of cows being milked while pregnant. Using my herd as an example, 36% (159 of 436) of my cows being milked are pregnant. This number usually ranges from the 35-50% in herds that don't calve seasonally. 13% of my herd is from 1-100 days pregnant, 15% are from 101-200 days pregnant and 9% are over 200 days and like I said earlier, we don't milk anything that is 60 or fewer days to calving.
And that's all without considering that peak production occurs from 100-150 days post calving when any pregnant cows are in the earliest stages of pregnancy. There is a 25 pound difference in daily production between my peak milk production/non-pregnant or early pregnancy cows (81 lbs/day) and cows that have been pregnant over 200 days (56 lbs/day).
So take what you will from my own information. I'm fairly typical, though seasonal calving herds like in New Zealand will be different as almost all milking cows are in the same stages of lactation and pregnancy in seasonal calving herds. I just think that the article posted blows things out of proportion and at worst is downright misleading considering that nobody milks cows straight through a pregnancy.