Alternative feed for livestock: Producing more animal protein with less climate and resource impact
Background
Global demand for animal protein continues to grow and is projected to increase by 60 to 70 percent by 2050 (FAO, 2019). Much of the increase will come from developing countries, due to increasing population, rising income, and urbanization. The heightened demand has increased requirements for livestock feed and other resources; however, feed production has been associated with deforestation, biodiversity loss, unsustainable resource extraction, and in particular climate change. Livestock-related emissions are estimated to contribute 11.1 to 19.6 percent of anthropogenic greenhouse gases, with a substantial portion originating from feed production and provision. Additionally, feed accounts for up to 60 percent of all farm expenses and has significant implications on livestock productivity. In this context, producing more meat, milk, and eggs for human consumption with fewer unintended consequences on the planet requires all workable solutions. Developing alternative feed is a viable option.
Why Alternative Feed
Alternative feed is broadly defined as biomass materials that can be fed to livestock to support maintenance and production requirements while improving agrifood system efficiency, contributing to the circular bioeconomy, and limiting competition of natural resources with human food production.
As such, alternative feed is primarily sourced from biomass materials that are unfit for human consumption, whether due to nutrient content and availability, palatability, or general consumer acceptability. Some examples include crop residues, such as straw or corn fodder remaining after grain harvest; post-harvest food handling or sorting discards which fail to meet quality control standards; byproducts or processing residues from the food, fuel, or fiber industries; supermarket unsellable products which are expired, damaged, or oversupplied; and other novel feed ingredients developed through scientific and technological innovation. As alternative feed ingredients originate from biomass that already exists from the cultivation of various agricultural products, they require minimal to no additional land, water, fertilizer, or pesticides.
Alternative feed ingredients can be substituted for conventional feedstuffs in livestock diets, consequently sparing resources and reducing greenhouse gas emissions. For example, feeding sustainable diets consisting of 8.6 percent thermally treated supermarket food waste could reduce land use by 13 percent, water consumption by 7 percent, and carbon emissions by 6 percent per market hog produced, compared to corn and soybean meal diets used in the conventional U.S. swine production system (Shurson et al., 2022).
Additionally, developing alternative feed ingredients from otherwise wasted or underutilized biomass materials not only reduces landfill emissions, but also helps to create a resilient, secure, and sustainable feed supply with locally-available feed materials. As these materials are usually inedible, unpalatable, or no-longer fit for human consumption, their upcycling via livestock further allows the conversion of nutrients contained in the biomass into meat, milk, and eggs for humans.
Research At Penn Vet on Alternative Feed
Approximately half of global fruits and vegetables produced are lost or wasted in the food supply chain before reaching consumers. This leads to tremendous management, resource, and environmental burdens. Our team at Penn Vet worked with local food supply stakeholders to develop novel ways to effectively utilize fruit waste from a local processing and distribution center as alternative feed for dairy cattle. In our first feeding study (Baker et al., 2024), fresh citrus waste was added to lactating cow diets at 7.1 kg per cow per day and fed for 24 days at our research dairy facility, in comparison with the standard (control) diet. The fruit-containing diet supported milk production with the same milk yield, milk fat and protein contents compared to cows fed the standard diet. Meanwhile, there was a feed cost savings of 37 cents per cow per day when feeding the fruit diet, or over $21,500 savings when calculated for the whole herd (160 cows) on an annual basis. Additionally, to feed the lactating herd for an entire year, citrus waste as an alternative feed would total 415 tonnes. The amounts of conventional ingredients including corn, corn silage, soybean meal, and other feeds to be displaced due to inclusion of the alternative feed would spare fourteen ha of cropland, 944 kg of N fertilizer, 480 kg of P fertilizer, and 40 kg of herbicides. Carbon mitigation would total 387,360 kg CO2-e, much of which is attributed to emission offset due to citrus waste diverted away from landfills and toward the farm as cattle feed.
Our second study was conducted at a commercial dairy farm, where fresh fruit waste was co-ensiled with grass hay to prevent spoilage and preserve feeding value (Baker et al., 2024). Subsequent use of the fruit silage in lactating cattle diets supported milk production levels similar to the control diet while lowering feed cost. More recently, we completed a third study with results providing evidence that fruit silage could be incorporated into lactating cow diets at up to a 22 percent inclusion rate without disrupting animal performance or enteric methane emissions, thereby positively enhancing circular and sustainable dairy production.
Our team also examined results from >100 animal feeding studies from about 30 countries (Wang et al., 2024); those studies included various food-producing animal species fed a variety of alternative feed ingredients at various rates. The field-based primary data were normalized to discern patterns and trends. In 75 to 77 percent of all cases, animals performed either as optimally or increased productivity compared to those fed the standard control diet; the remaining 23 to 25 percent had decreased performance. Ultimately, balancing major nutrients from all feed ingredients is integral in maintaining animal productivity when incorporating alternative feed in the pursuit for sustainable livestock production.
Our latest research investigated re-purposing food waste to animal feed (re-feed), composting, or anaerobic digestion for their respective carbon and resource impacts. Using data from field-based studies conducted under diverse conditions worldwide, we found collective evidence that composting, anaerobic digestion, and re-feed provide emission reductions of about 1 t CO2-e percent food waste recycled, compared with landfill disposal. Emission mitigation capacity resulting from no landfill disposal in the United States, EU, and China could offset 10 percent, 5 percent, 17 percent of the emissions from these large agricultural systems, respectively. In addition, re-feed could spare enormous amounts of land, water, agricultural fuel, and fertilizer use. Our findings provide a benchmark for countries developing food waste management strategies for a circular and sustainable agrifood system.
There exist massive amounts of diverse biomass materials in our agrifood system as well as in nature that remain underutilized or wasted. Although unfit for direct human consumption, the biomass and carbohydrates, lipids, proteins, and minerals contained in it can be upcycled through livestock feeding. Alternative feed ingredients developed from these biomass materials can help decrease the dependence and use of conventional feedstuffs while mitigating carbon footprint and resource burdens. To enable widespread adoption of the sustainable solution, concerted effort is required, for example, the R&D community to develop low-cost processing technologies that convert suitable streams of raw biomass materials into safe and nutritious alternative feed; extension and education agents to engage livestock farmers and managers with field-based recommendation and guidelines; and animal nutritionists to assist end users of alternative feed for sustained productivity and profitability. Importantly, to seize the opportunity of developing alternative feed for producing more animal protein with less unintended impact requires strong policy support. Effective policies should include not only laws and regulations regarding feed safety and animal health, but also provide economic incentives and infrastructure development and support to facilitate entrepreneurship and create businesses for sustained operation. Amid an escalating climate crisis and resource constraints, it is up to us to have the courage to take actions and overcome challenges.
