Cattle get a bad rap in public discourse on agriculture’s carbon footprint. However, many of those arguments assume that everything that cows eat has been grown exclusively for that purpose and has been shipped great distances. That’s just not the case. Most dairy farmers are taking actions that reduce contributions to atmospheric carbon.
On the modern American dairy farm, the cows are eating a lot more than grass. Their diets are carefully balanced for their age, stage of lactation (how many days since they started producing milk), time of year, and other variables. Just like a hundred years ago, their diet can change over the course of the year, depending on what is available and affordable to the farmer. A typical milking cow’s diet will contain roughage (plant material—often grown on the farm—like hay and silage [fermented plant material, rather like sauerkraut] made from whole corn plants or from grasses and legumes like clover or alfalfa). Also on offer would be a concentrated source of energy, like grain (corn, wheat, barley, oats, etc.) plus some minerals to make sure their nutritional requirements are being met.
Another source of nutrition for cows are byproducts from the processing of other agricultural products. What is that exactly? Some examples are the meal that is left over after the oil has been pressed out of soybeans or canola, brewers’ and distillers’ grains, rice hulls, citrus pulp, cottonseed, cannery waste from vegetable processing, bakery waste (the old stale stuff), and even whey (from making cheese or yogurt). Byproduct ingredients will vary by location: a dairy in California might include almond hulls in their cows’ diet while potato waste is a more common component for cows in Idaho. These ingredients can be blended into the cows’ diet in quantities determined by the farm’s nutritionist. (Yes, most dairies have a nutritionist.) The other fate for these byproducts is compost, but more likely they would end up in a landfill, decomposing and directly releasing greenhouse gasses.
On average, 32% of a milking cow’s diet in the U.S. is byproduct feed. Nearly one-third of her daily diet is coming from crops that have already been planted, tended, and harvested for another purpose. For the same carbon footprint of that agricultural commodity, say sugar beets as an example, we get sugar and some milk (from the nutrition provided by the beet pulp byproduct). The milk is a bonus!
Often, a byproduct feed can be sourced closer to the dairy than the diet component(s) it is replacing. For a dairy on the west coast, more locally produced beet pulp or citrus pulp can replace some of the corn in the diet that is transported from the Midwest, providing an additional reduction in the carbon footprint of a gallon of milk. If a dairy is located close to a brewery or potato chip factory, then brewers’ grain or potato-processing waste could provide nutrition with even less CO2 generation due to fewer miles traveled.
Indeed, byproduct feeds can never compose the entirety of a cow’s diet. Crops such as corn, alfalfa, and grasses will continue to be planted and harvested solely as cattle feed. As they grow, however, these plants pull CO2 from the atmosphere as participants in the carbon cycle. Unlike other sectors that emit greenhouse gases, agriculture routinely transfers carbon from the air into food and fiber for humans, into food for animals, and into the soil. Furthermore, research is ongoing on how to decrease milk’s carbon footprint, with studies examining feed additives that reduce methane production (Can we alter the metabolism of the methane-producing microbes living in the cow stomach?) and the genetic contribution to methane production (Can we select cows with lower methane output?) among others.
Trying to account for every molecule of greenhouse gas that is generated for a gallon of milk is an exhausting exercise, but those calculations must reflect what cows are actually eating. Dairy farming fits into a larger agricultural network of resource utilization and generation, one that is constantly evolving.