The Link Between Dairy Cow Nutrition and Methane

Animal agriculture in general and ruminants in particular are considered to be a key contributor to excessive greenhouse gas (GHG) accumulation.

Photo: aurielaki/istock

Environmental concerns over increasing levels of methane emissions into the atmosphere constitute much of the discussion on climate change. Animal agriculture in general and ruminants in particular are considered to be a key contributor to excessive greenhouse gas (GHG) accumulation. The U.S. dairy industry must address the issue of methane coming from cows and heifers.

Total U.S. GHG emissions were reportedly 6,870 million metric tons (MMT) of carbon dioxide (CO2) equivalent in 2014. (This calculation includes methane CH4 and nitrous oxide at an equal value of heat-absorbing capacity as CO2. Methane is over 20 times more potent as a GHG in part due to its ability to retain heat compared with CO2. A small amount of methane represents a large amount of CO2 equivalent.) Methane emissions from U.S. dairy cattle were reportedly 41.9 MMT of CO2 equivalents in 2014 – or 5.7 percent of total methane emissions.

The U.S. dairy industry contributes a small percentage of the total GHG. Livestock worldwide, however – which are largely dairy and beef cattle – are considered to contribute closer to 20 percent of total GHG due to poorer nutrition management and higher percentages of grazing. Clearly, U.S. dairy cows are not the most guilty party when it comes to GHG. However, the U.S. dairy industry has committed to decreasing methane emissions by 25 percent by the year 2020.

How to lower enteric methane

A paper presented at the 2016 Cornell Nutrition Conference by Dr. Larry Chase outlines a number of nutrition and herd management options that have the potential to lower enteric methane in the dairy industry:

  • Increase productivity and feeding efficiency, which results in more milk per cow and the need for fewer cows to produce a set quantity of milk.
  • Improve forage quality, which will result in lower NDF levels in diets. Certain types of grasses produce higher levels of methane based upon carbon structure in those grasses.
  • Consider corn silage with higher digestibility has been shown to lower enteric methane.
  • Process grains to improve starch digestibility in the rumen
  • Feed ionophores to improve the energy status of cows and heifers and reduce methane production from rumen microbes.
  • Rumen inert fats may improve energy status requiring less fermentation in the rumen.
  • Rumen modifiers may offer the opportunity to alter the rumen microbial population.
  • Implement herd grouping and ration formulation strategies to improve efficiency of nutrient use.
  • Decrease the age at first calving for replacement heifers, which would lower total animal numbers in dairy herds.
  • Implement feeding management practices that improve consistency and minimize variability.
  • Provide facilities and herd management systems that improve cow comfort and reduce stress.
  • Improve herd health and reproductive performance.

The average Holstein dairy cow is reported to release ¾ to over 1 pound (373 to 509 grams) of enteric methane per day depending upon the level of milk production. Enteric methane is the methane produced in the digestive tract of cows and is released into the atmosphere by flatulence from the colon or belching from the rumen. Methane production is highly correlated to feed intakes, and since lactating dairy cows consume large amounts of feed with the goal of producing milk, milk production accounts for over 50 percent of the methane emissions from dairy farms. Therefore, the primary area of focus for reducing methane in the dairy industry centers on lactating dairy cow diets and nutrition.

Ruminant nutritionists have a tricky situation with regards to lowering enteric methane. Decreasing enteric methane requires altering the rumen microflora, which could have a deleterious effect on cow health and milk production. Methane is a naturally occurring biological byproduct of fermentation in the rumen and intestines. Chart 1 shows that as milk production increases, total grams of enteric methane produced climbs with it. This is directly a result of a cow consuming more feed to produce the milk. Certainly cows that produce more milk will produce more enteric methane. Chart 2, however, shows that as milk production increases, grams of methane produced per pound of milk decreases. This indicates that as a cow’s milk production increases, less methane is produced in the rumen.

This efficiency is not fully understood but can be partly explained by the fact that lactating diets formulated for higher levels of milk production usually contain more grains and commodity byproducts, which are known to produce less methane than high-forage diets. High forage diets create more enteric methane. Research supports the conclusion that feed rations higher in NDF tend to increase methane emissions, while higher starch rations tend to decrease methane emissions.

An area of dairy management that should be aggressively addressed for dairy farm productivity and profitability as well as assisting in the reduction of methane production is that of improving conception rates and lowering average days-in-milk in herds. Cows with shorter, more productive lactations will improve overall milk production on dairy farms, reducing the need for high inventories of heifers, the second largest source of methane on the dairy. Although it’s impossible to completely eliminate enteric methane emissions coming from dairy cows, dairy farms that focus on both feeding and reproductive efficiencies automatically reduce methane production that will lower the carbon footprint from the dairy industry.

According to Dr. Chase, research shows that a 2,000-pound increase in milk production during a cow’s lactation results in a 1 percent decrease in the carbon footprint on a dairy farm. A herd with average annual milk production of 20,000 pounds that incorporates summer grazing had a carbon footprint similar to a confinement herd producing 26,000 pounds of milk or more. Ironically, an all-grass herd producing 16,000 pounds of milk had a carbon footprint similar to the summer grazing and confinement herds described already. This research contradicts the current sentiment favoring pasture grazing systems for dairy cows as being advantageous to environmental sustainability and a more eco-friendly means of producing dairy products. This objective approach of evaluation should be used more frequently by the industry to examine alternative farm management strategies that will result in a more proactive approach to reducing methane emissions from the dairy industry.

Read more: Executing the Perfect Manure Management Plan