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Low Impact Milk

In 2008, the U.S. Dairy Sustainability Initiative was launched, representing about 80% of producers. Their goal?  To reduce greenhouse gas emissions associated with milk product by 25% by 2020 while improving life for dairy farmers.  It seems like a big goal, but it’s something the dairy industry has been doing for decades, primarily by improving production on a per animal basis.  To reach the new goal, researchers and producers are looking at these three things: 1) Feed, 2) Manure Management, and 3) Milk Yield.  The challenge is that when you tweak one part of the system, there can be good and bad consequences in another.  It’s a balancing act that will require some thought and some interesting choices.



Feed production, with use of fertilizer and diesel, makes up about 43% of the footprint of milk. It affects how much milk is made and the quality and quantity of manure.

It's not too easy measuring methane outputs, but that hasn't stopped us from trying!
It’s not too easy measuring methane outputs, but that hasn’t stopped us from trying!

A lot of that can be attributed to corn production’s fuel, electricity, pesticides, and fertilizers and other soil amendments. On the other hand, corn is a high quality feed that reduces the amount of methane produced in the rumen and released in burps and farts by cows. (Need more on the importance of this whole methane burps and farts thing?  Read our past article “Are Cow Farts Destroying the Planet?”.)

Following right behind corn is grass production, beating out other forage crops. Grass doesn’t measure up well because even though it doesn’t need as many inputs, it also doesn’t yield as much as other forage crops. It is also not as high quality feed, increasing the amount of methane produced by cows.

But there’s almost never bad news without some good news too.  Carbon sequestration in pasture soils might also reduce the footprint of grass production.  The problem is that some research has shown that mature pastures reach a saturation point where carbon sequestration levels off. Farmers and scientists are looking for ways to goose that model and kick sequestration up a notch. Because carbon levels of mature pastures and fields are at a pretty steady state, most studies measuring dairy’s footprint don’t take carbon sequestration into account.

Additives can also reduce methane production by improving digestion of lower quality forages. One additive that is readily available is monensin (sold as Rumensin).  This additive fights coccidiosis and helps cows gain more with less feed. Essentially, it can improve their feed efficiency, reducing greenhouse gases by 7%. The list of other additives is pretty interesting and includes things like oregano, cashew shells, steam flaked corn, glycerol, and hops. Cashew shells reduced methane emissions by 20% and oregano dropped it by 40%. The challenge would be in getting these additives to the producer. Providing fats and oils lowered methane, and reduced the dry matter the herd needed, regardless if the fats were fed as seed or as oil, saturated or not.  The bonus of this strategy is that some oils, like flax seed, also improve milk’s nutritional value, adding more omega-3 fatty acids and reducing saturated fats.

Researchers are also looking at feeding strategies that reduce feed quantities and the associated greenhouse gas impacts.  One strategy that showed promise was feeding more concentrates and less dry matter. By reducing feed for heifers, and  feeding 80 or 90% of the typical dry matter (but 100% of the protein and nutrients) they increased feed efficiency and daily gain. Manure dry matter (and manure is 80% wet) dropped by two pounds per cow per day. When they were milked, there was no statistical difference in milk production, but it did look like feeding less made more milk. Still, the herd was very vocal, especially the first few weeks. Hearing the herd hungry might not go over too well with most folks, so you might prefer to do this with young animals who don’t already expect a certain amount and kind of food from you. And definitely, consult with a nutritionist if it’s something you’d consider.

Texas AgriLIfe Research photo by Dr. Pablo Pinedo
Texas AgriLIfe Research photo by Dr. Pablo Pinedo

One more option for reducing milk’s carbon footprint is to consider breed and size. Every cow takes a certain amount of feed just for maintenance, with smaller cows needing less. Holsteins need about 13 lbs of DM per day, and Jerseys need 10. The more milk each cow makes, the more that maintenance feed and its GHG footprint gets diluted. Smaller cows may have a smaller footprint, so switching from Holsteins to Jerseys can reduce GHG by 20%.

Manure Management

Grahpic courtesy of NW Farms & Food
Graphic courtesy of NW Farms & Food

Feed can affect the quality of manure and how manure is managed affects how much of manure-nitrogen volatilizes, releasing nitrous oxide, another greenhouse gas. Manure also produces methane.  Some scientists find that manure released directly onto pasture forms a crust which limits N2O volatilization, while spreading liquid manure on the surface of fields may accelerate volatilization. Warmer temperatures spur the release of more nitrogen.

Liquid manure storage promotes methane production.  The good news is that methane digesters can take advantage of the methane in manure, turning it into energy, and composting manure  provides an alternative storage method and soil amendment.  The United States Department of Agriculture and the Innovation Center for U.S. Dairy are working together to improve this technology and make it more accessible to more producers, awarding grants and providing loans for installation of digesters across the country.

Increasing Milk Yield

This is probably the most controversial part of this topic because it involves injecting cows with rBST. The use of rBST can increase milk production from 11%–16%.  That means that a cow that could provide enough school lunch milk for 125 kids, can serve 145 kids when injected with rBST.  The problem is that studies done by university researchers and scientists at Monsanto, the maker of rBST, have shown a nearly 25% increase in the risk of clinical mastitis, a 40% reduction in fertility and 55% increased risk of developing clinical signs of lameness. The same study reported a decrease in body condition score for cows treated with rBST even though there was an increase in their dry matter intake.  If you consider just the increases in milk yield, we get an 8% reduction in greenhouse gases.  But the increase in illnesses also carry a cost.  Feed efficiency drops by 40% for an animal with mastitis. Sick animals take a lot more feed (read: GHG) for maintenance.

All these strategies drop greenhouse gases and could improve the bottom line. The question is: do any of them work for you? We’d love to see a discussion about what you think might work, and how we can get to the 25% reduction in greenhouse gases by 2020.

Editor’s note: A great resource, if you have the time, is this video, by Professor Mike Hutjens at the University of Illinois. 

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Rachel Gilker
Rachel Gilker
Rachel's interest in sustainable agriculture and grazing has deep roots in the soil. She's been following that passion around the world, working on an ancient Nabatean farm in the Negev, and with farmers in West Africa's Niger. After returning to the US, Rachel received her M.S. and Ph.D. in agronomy and soil science from the University of Maryland. For her doctoral research, Rachel spent 3 years working with Maryland dairy farmers using management intensive grazing. She then began her work with grass farmers, a source of joy and a journey of discovery.


  1. Great article, like that both sides of the grass/grain debate are addressed.

    One comment I’d like to make regarding rBST…if I recall correctly from my dairy science classes, the increased risk of mastitis, lameness, and infertility for cows treated with rBST was not different to a cow that naturally produced that much milk. I.e. a cow going from 80 to 85 lb/d with rBST has the same risk of issues as a cow naturally producing 85 lb/d with no rBST. It requires more work from the farmer, that’s for sure…but to my best knowledge, rBST is not making cows sick in and of itself.

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