Study examines carbon impact of vegetable by-products in bull diets

Researchers in Spain are testing a practical climate question for beef production: can locally sourced vegetable by-products lower the carbon footprint of finishing cattle without undermining production goals? In the Animals paper, “The Carbon Footprint of Finishing Yearling Bulls Fed a Diet Containing Vegetable By-Products in Navarra, Spain,” the authors compared a conventional finishing diet with one containing vegetable by-products in yearling bulls. The study sits within a Navarra-based effort to use food industry leftovers as feed ingredients rather than waste streams. (agroinforma.ibercaja.es)

That didn’t come out of nowhere. Navarra is a major vegetable-producing region with a sizable processing industry, and local beef producers have been exploring these by-products for several years as an alternative to conventional ingredients such as barley and soy. A BovINE good-practice case study described the use of ensiled vegetable industry by-products, including carrots, peas, and lettuce, in finishing diets for Pirenaica cattle in Azoz, Navarra, beginning around 2020. The same case study said producers were drawn by lower feed costs, fewer digestive disorders, and the chance to build rations around local inputs. (hub.bovine-eu.net)

The new carbon-footprint paper also fits into a broader research program from the Public University of Navarra and collaborators. An earlier paper from the group evaluated the nutritive value, digestibility, and rumen fermentation characteristics of vegetable by-products generated in high volume in the Ebro Valley, including beans, broccoli, carrot, cauliflower, chickpea, green bean, peas, pepper, potato, and spinach, then used selected mixes to formulate a calf-fattening ration. A separate 2024 Agricultural Systems paper from overlapping authors reported that a by-product-based diet reduced blue water use in Ternera de Navarra PGI beef production, suggesting the environmental case for these feeds may extend beyond carbon alone. (pmc.ncbi.nlm.nih.gov)

Industry and academic reaction around the Navarra work has emphasized that feed changes can affect more than emissions. Reporting on Irantzu Goenaga Uceda’s doctoral research said the by-product-based diet improved the nutritional and sensory profile of the resulting meat while also reducing environmental impact. In the BovINE case study, the farmer involved said the experience had been positive, and the platform summarized UPNA findings as showing no loss of meat quality. Those are encouraging signals, although they come from project and sector channels rather than independent commentary, so they should be read as supportive context, not external validation. (agroinforma.ibercaja.es)

Why it matters: For veterinary professionals, especially those advising beef operations, this is a reminder that sustainability conversations are moving closer to the ration bunk. Feed often represents a major share of livestock’s environmental burden, and by-product feeding is being framed as one way to cut waste, reduce reliance on human-edible feed materials, and potentially improve resilience to volatile commodity markets. In practice, though, veterinarians will care about the tradeoffs: consistency of by-product supply, nutrient variability, storage and ensiling quality, mycotoxin and spoilage risks, rumen adaptation, and the real-world effects on daily gain, health events, and carcass outcomes. (hub.bovine-eu.net)

There’s also a bigger systems point. The Navarra model appears to work in part because the cattle, feed sources, and vegetable processing sector are geographically close, which may help lower transport burdens and improve circularity. That means the findings may be most transferable to regions with similar agri-food infrastructure rather than serving as a universal template. Even so, the concept aligns with a growing body of work suggesting that by-products and co-products can reduce feed costs and, in some settings, support more sustainable cattle production. (hub.bovine-eu.net)

What to watch: The next questions are whether the carbon-footprint advantage holds up when producers account for ration variability, preservation losses, and enteric methane, and whether regulators, PGI programs, or supply-chain buyers begin treating by-product-based feeding as a measurable sustainability attribute. (academica-e.unavarra.es)