Dairy Cows Recycle Valuable Nutrients in US Agricultural Byproduct Feeds

Written by: Guest   |   November 3, 2021

Environmental footprint, Dairy, Guest perspective

By: Juan Tricarico, Ph.D., vice president of sustainability research, Dairy Management Inc.

The fact that dairy cows eat agricultural byproduct feed is not news. For example, dairy cows have been recycling distiller’s grains for as long as humans have been fermenting grains and distilling ethanol from them. What IS news, however, is that dairy cows are now starting to get recognition for their role as valuable nutrient recyclers in the agricultural system because of this practice. 

Conceptually, the practice of including agricultural byproduct feed in dairy cow diets makes a lot of sense. The dairy cow is a ruminant, meaning it has a complex four-chambered stomach, and as such, is capable of digesting highly fibrous leftovers from major and specialty agricultural crops that don’t make it into human food products (think: grass, almond hulls, distillers grains, etc.).  However, understanding the concrete benefits afforded by this practice requires knowing how much and what types of byproduct feeds dairy cows eat. This is the first of a few questions that Mary Beth de Ondarza and I answered in a recent study published in the Journal of Cleaner Production.

We sent questionnaires to dairy nutrition consultants and feed industry representatives in the United States regarding their usage of 63 different byproduct feeds as well as the number of lactating cows and milk production of the dairies they served. The survey responses, along with calculations to derive estimates of nutrient supply and greenhouse gas emissions, offered the following insights:

• The survey captured data from roughly 33.5% of U.S. lactating cows and 35.7% of U.S. milk production in 2019, making dairy cows the most comprehensive user of U.S. byproduct feeds.
• Ruminal digestion offers dairy cows a wider menu of byproduct feeds than what simple-stomached poultry and swine can digest and fully utilize (Figure 1 below).  
• U.S. dairy cattle consume 12 kilograms as-fed (8.2 kg dry matter) of byproduct feed per milking cow (i.e., lactating cow in addition to associated dry cows and replacement heifers) and 319 grams as-fed (219 g dry matter) of byproduct feed per kg milk produced. 
• Cows in the West consume the most followed by the South, Northeast and the Midwest, reflecting regional variations in byproduct feed costs, availability and ability to manage byproduct feed on the farm.
• In 2019, U.S. milk cows ate between 32- 41 million metric tons (as-fed) of byproduct feed based on either U.S. Department of Agriculture-estimated milk production or milk cow numbers.
• Byproducts supply 32% of the dry matter, 37% of the energy and 54% of the protein needed by U.S. lactating cows.
• Roughly 70 g of carbon dioxide-equivalent (CO2-eq) per kg of byproduct (dry matter) are emitted in the forms of enteric methane and manure methane and nitrous oxide when byproducts are fed to U.S. milking cows to partially replace forages and whole grains. Alternatively, landfill disposal, composting and combustion emit 3448, 328, and 31 grams of carbon dioxide equivalents per kilogram of byproduct dry matter.

The bottom line is that dairy cattle consume substantial amounts and a wide variety of byproduct feed and are an effective vehicle to recycle valuable nutrients in agricultural byproduct streams that are either indigestible by humans or undesirable for direct human consumption.

They effectively turn this into milk and dairy foods, following current recommendations for the sustainable management of unavoidable wasted food. Also, since byproduct feeds are substituted for some forages and grains in dairy cows’ diets, minimal long-term emissions of enteric methane and manure methane and nitrous oxide are generated by this practice.

I encourage the feed industry to review this study/article and let me know if you have questions in the comments below. It is critical to share this important information with stakeholders outside of the feed industry for them to understand the ways our industry is working to reduce food loss and waste, closing the food supply cycle and providing nutritious food for Americans.