Is There Really Pus in Milk?

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What does the “milk pus test” tell us about the U.S. milk supply?

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Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Dairy cows might normally live for about 20 years, but they are typically slaughtered for hamburger after they’re just a few years old when they produce less milk and their profitability drops. But another leading cause of cow culling is mastitis––udder inflammation and infections––which affects 99.7 percent of all dairy operations in the United States.

Because of the mastitis epidemic in the U.S. dairy herd, the dairy industry continues to demand that American milk retain among the highest allowable “somatic cell” concentration, nearly twice as much as the rest of the world—750,000 cells per milliliter.

The concentration in milk from healthy udders should be less than 100,000. These somatic cells are mostly white blood cells, so when you get up to around 200,000, which is like a million per teaspoon, the udder is likely to be infected. So, the somatic cell counts in the bulk milk tanks reflect the level of infection. Basically, if the bulk milk tank, which can hold thousands of gallons, averages 200,000 then 15 percent of the contributing cows are likely infected. At a concentration of 400,000, which is more in line with international standards, a third of the cows are likely infected. And staying within the 750,000 U.S. limit for Grade A milk could reflect that about two-thirds of the cows are infected.

Now somatic cells are not synonymous with pus cells, as has sometimes been misleadingly suggested. Just as normal human blood and breast milk contain low levels of white blood cells, so does milk from healthy cows. That’s something we’ve known about for more than a century. The problem is that many of our cows are not healthy.

According to the latest national government survey, about one in four dairy cows in the United States suffers from clinical mastitis, the second leading cause of death on dairy farms. This is why the average somatic cell concentration of U.S. milk is that of a likely infected udder at 204,000 cells per milliliter. How much actual pus does that translate to?

Although the industry doesn’t like to talk about pus cells, the fact that pus is present in milk from inflamed mammary glands is a given. But what constitutes pus in milk? The quote-unquote “milk pus test” was introduced more than a century ago. It pooled milk from infected cows that was estimated to contain up to 2.5 percent pus by volume. And we’d really like to see no more than like 0.1 percent. So, what does 204,000 cells per milliliter, the national U.S. average, translate to?

That’s a million cells per teaspoon of milk. A million cells per spoonful sounds like a lot, but pus is really concentrated. So, how much pus is there in a glass of milk? Not much. If you take the national average and subtract the number of white blood cells you might see in normal milk, you get about 100,000 inflammatory white blood cells per milliliter, or about 25 million per cup. Then it just depends on the cellular concentration of pus.

Although straight pus may have 80,000 cells per microliter or less, to be conservative, the most concentrated I could find for straight pus was about 150,000. Note that’s per microliter, not per milliliter. So, if there are about 25 million cells per cup, and a microliter of pus contains about 150,000 cells, that would come out to be about 150 microliters of pus per glass of milk. There are about 50 microliters in a drop, so there’d only be a few drops of pus per glass on average.

And you can apparently taste the difference. One of the major problems associated with mastitis is the flavor and texture defects. Milk with high somatic cell counts looks the same, but evidently doesn’t smell or taste as good.

The large amounts of pus in mastitic milk may be aesthetically objectionable, but it’s important to note this is not a food safety issue, thanks to pasteurization. The dairy industry emphasizes that ingesting large amounts of bovine white blood cells has not been shown to be harmful. No matter how inflamed and infected udders get, the pus gets cooked. But just as parents may not want to feed their children fecal bacteria in meat, even if it’s irradiated fecal bacteria, as the Director of the Food Policy Institute put it: “Irradiated poop won’t make you sick, but it’s still poop.” Parents might not want to have their children sip pasteurized pus.

Please consider volunteering to help out on the site.

Motion graphics by Avo Media

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Dairy cows might normally live for about 20 years, but they are typically slaughtered for hamburger after they’re just a few years old when they produce less milk and their profitability drops. But another leading cause of cow culling is mastitis––udder inflammation and infections––which affects 99.7 percent of all dairy operations in the United States.

Because of the mastitis epidemic in the U.S. dairy herd, the dairy industry continues to demand that American milk retain among the highest allowable “somatic cell” concentration, nearly twice as much as the rest of the world—750,000 cells per milliliter.

The concentration in milk from healthy udders should be less than 100,000. These somatic cells are mostly white blood cells, so when you get up to around 200,000, which is like a million per teaspoon, the udder is likely to be infected. So, the somatic cell counts in the bulk milk tanks reflect the level of infection. Basically, if the bulk milk tank, which can hold thousands of gallons, averages 200,000 then 15 percent of the contributing cows are likely infected. At a concentration of 400,000, which is more in line with international standards, a third of the cows are likely infected. And staying within the 750,000 U.S. limit for Grade A milk could reflect that about two-thirds of the cows are infected.

Now somatic cells are not synonymous with pus cells, as has sometimes been misleadingly suggested. Just as normal human blood and breast milk contain low levels of white blood cells, so does milk from healthy cows. That’s something we’ve known about for more than a century. The problem is that many of our cows are not healthy.

According to the latest national government survey, about one in four dairy cows in the United States suffers from clinical mastitis, the second leading cause of death on dairy farms. This is why the average somatic cell concentration of U.S. milk is that of a likely infected udder at 204,000 cells per milliliter. How much actual pus does that translate to?

Although the industry doesn’t like to talk about pus cells, the fact that pus is present in milk from inflamed mammary glands is a given. But what constitutes pus in milk? The quote-unquote “milk pus test” was introduced more than a century ago. It pooled milk from infected cows that was estimated to contain up to 2.5 percent pus by volume. And we’d really like to see no more than like 0.1 percent. So, what does 204,000 cells per milliliter, the national U.S. average, translate to?

That’s a million cells per teaspoon of milk. A million cells per spoonful sounds like a lot, but pus is really concentrated. So, how much pus is there in a glass of milk? Not much. If you take the national average and subtract the number of white blood cells you might see in normal milk, you get about 100,000 inflammatory white blood cells per milliliter, or about 25 million per cup. Then it just depends on the cellular concentration of pus.

Although straight pus may have 80,000 cells per microliter or less, to be conservative, the most concentrated I could find for straight pus was about 150,000. Note that’s per microliter, not per milliliter. So, if there are about 25 million cells per cup, and a microliter of pus contains about 150,000 cells, that would come out to be about 150 microliters of pus per glass of milk. There are about 50 microliters in a drop, so there’d only be a few drops of pus per glass on average.

And you can apparently taste the difference. One of the major problems associated with mastitis is the flavor and texture defects. Milk with high somatic cell counts looks the same, but evidently doesn’t smell or taste as good.

The large amounts of pus in mastitic milk may be aesthetically objectionable, but it’s important to note this is not a food safety issue, thanks to pasteurization. The dairy industry emphasizes that ingesting large amounts of bovine white blood cells has not been shown to be harmful. No matter how inflamed and infected udders get, the pus gets cooked. But just as parents may not want to feed their children fecal bacteria in meat, even if it’s irradiated fecal bacteria, as the Director of the Food Policy Institute put it: “Irradiated poop won’t make you sick, but it’s still poop.” Parents might not want to have their children sip pasteurized pus.

Please consider volunteering to help out on the site.

Motion graphics by Avo Media

Doctor's Note

For more on what’s in milk, see:

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