Methanogenesis

Sometimes, it seems one has to be a weirdo to even have a chance at fame.

Take Heather Mills, for example. She’s quite the animal activist, and from what I’ve seen, she often makes claims that would be odd if she were kidding, but she’s not kidding. Her crusade for the seals have taken a back seat to cows. There are some 1.3 billion cows, and such a large number of cows produce a heck of a lot of methane. The problem is, methane kicks carbon dioxide’s ass as a greenhouse gas.

Australia’s The Age newspaper published an article titled, “Mills asks: why don’t you drink rats’ milk?” in which she says,

There are 25 alternative milks available in health shops and supermarkets. Why don’t people stop drinking cows’ milk lattes? Why do we not drink rats’ milk, cats’ milk, or dogs’ milk?

Of course rats don’t emit as much methane as cows. Has she considered they also don’t produce as much milk? Has she looked into the environmental impact of the number of rats required to produce the same amount of milk we currently get from cows? Of course not. She’s just shooting off her mouth to court the spotlight. It seems the research into a bovine diet to reduce cows’ methane output isn’t worthy of notice.

Shit, she’s a vegan and doesn’t drink milk. Typical lefty wing nut… quick to propose a solution that involves telling other people how they have to change. You think she’s eco aware? She might be aware, but the awareness doesn’t translate into action. According to This is North Scotland, she left her Mercedes 4x4 SUV running outside while she was giving interviews about how evil cow’s milk is.

I’ve got a question for her that starts with, “Why don’t you …” but it has nothing to do with milk.

I like to figure things out. So with this in mind, let’s get back to the topic at hand, okay? It’s a shame Heather Mills would rather drive her Mercedes SUV to animal activist rallies than do some figuring of her own. She might not sound like such a damned fool if she did.

The average dairy cow in the United States produced 8800 kg of milk in 2005.¹ Glossing over the slight density difference between milk and water, let’s just say 8800 kg of milk equals 8800 litres. It’s close enough for our purposes.

The hard part was finding out how much milk rats produce. I finally discovered a 1975 Israeli study titled, “Effect of Litter Size on Milk Yield in the Rat.“² And before you ask, would I kid you? The study covers the early and late lactation periods which are from 6 – 10 and 11 – 15 days after birth, respectively. During this 10 day period, the lactating rats produced an average of 7.22 grams of milk in each eight hour period. This was the largest average milk yield, with a litter of 12. Litters of 3, 6, and 9 all had the dam produce less milk in total.

So over 10 days, we’re looking at 216.6 grams. Assuming rats can maintain this rate of milk production over the course of a year, and I have no reason to believe they can, they’d each produce 7905.9 grams of milk. This is 7.9 litres.

Divide a cow’s yearly yield of 8800 litres by a rat’s 7.9 litres and you’ll need 1114 rats to equal the milk production of a single cow. Given the 1.3 billion cows³ on Earth, we’d need 1.4 trillion rats to produce the same amount of milk. Sure rats don’t eat much, shit much, or fart much, but a trillion times nearly nothing is going to equal a big something!

And don’t forget that the rat milk yield I based my numbers on is the best average over ten days while the cow yield I used is the U.S. average over a year. If rats can’t be made to lactate at this rate indefinitely, the required number of rats will be much higher. Also, the inefficiencies in having to gather a comparatively small amount of milk from each of a far larger number of animals will drive costs through the roof.

Mills was speaking of dairy cows, but my numbers assume all cows are dairy cows. Of course this isn’t true, but I see no reason for Mills to object to dairy cattle methane and happily accept beef cattle methane. Therefore, I have to assume she’d be pleased to see us eating rat burgers. This skews the beef cattle portion even further because cows typically weigh in between 600 kg and 900 kg with very large steers tipping the scales at 1800 kg,⁴ while rats rarely exceed a mass of 500 grams.⁵ I don’t know the ratio of dairy to beef cattle in the world, but the beef portion requires even more rats per cow than the dairy.

What’s the difference between a famous personality like Mills and an average person who has no idea what he’s talking about? Mills has the fame to make certain many more people know she has no idea what she’s talking about.

1. “Dairy cattle,” posted on Wikipedia, retrieved 2007-11-26.
2. Morag, M., Popliker, F., Yagil, R., “Effect of Litter Size on Milk Yield in the Rat”, Laboratory Animals, Volume 9, Number 1, January 1975, pp. 43 – 47(5)
3. “Cattle,” posted on Wikipedia, retrieved 2007-11-26.
4. ibid
5. “Rat,” posted on Wikipedia, retrieved 2007-11-26.