Poultry and fish are both increasing in popularity as protein sources in human diets. Fish consumption has increased by 122% between 1990 and 2018 [1
] with an over 500% rise in aquaculture production globally over the same timescale. Salmon production is estimated to reach 2.7 million tonnes (MT) by 2021, compared to 0.8 MT in 2000 [2
]. Similarly, poultry meat production is also increasing year on year and is predicted to have reached 137 MT in 2020 [1
]. This rapid increase in the scale of meat production inevitably creates a conflicting global role for poultry and fish production: in rapidly increasing their contribution to UN Sustainable Development Goal (SDG) 2 (Zero hunger) and SDG 3 (Good health and wellbeing), the negative implications for SDG 12 (Responsible consumption and production) and SDG 13 (Climate action) are concurrently increased through increased resource use and pollution, respectively. Development of circular economies is an effective way to reduce the livestock and poultry pollution, improve the utilization efficiency of resources [3
], and to balance economic development and environmental protection [3
]. It is well recognised that the potential for extensive environmental impact from poultry production is substantial if a linear model is followed [4
] and the key to sustainable development in animal production is conversion of potential waste and pollutants into resources [4
]: negative externalities may be transformed into positives ones by identifying potential beneficiaries of waste streams [3
Historically, circular economy models involving poultry production have focussed on the waste (or, more appropriately, co-product) streams associated with meat or egg production. The scale and speed of bird growth on a modern poultry farms means that a single farm may produce more than 700 tonnes of manure each year. This volume far exceeds the volume that may be safely applied as fertiliser to surrounding arable land, leading to harmful levels of N and P levels in soil if application to land is continued [5
] or, if not managed properly, un-needed manure can be dangerous to the health of local waterways and the people who depend on them [5
]. The greatest focus of circular economy models involving poultry production has been on converting the litter (mix of manure and bedding) into energy via anaerobic digestion, combustion, pyrolysis and gasification [5
]. Waste management is now attracting increasing cooperation between multi-field stakeholders (including governments) to promote circular economy approaches [5
], for example through generation of innovative bio-based functional products from feather meal [5
] and egg shells [5
] and fish processing waste [5
]. While the outputs from fish and poultry production are increasingly incorporated into circular economies, the main input, feed, has moved away from a circular approach where by-products from other food production sectors were used to a high natural resource approach where soya beans are grown specifically for inclusion in animal feed. In order for meat production to develop sustainably, feed producers must revert to their traditional of using co-products from other industries.
Soy is one of the most internationally traded agricultural commodities, and is principally used globally as the protein component of animal feed [6
]. Brazil and the United States are jointly the world’s leading soy producers and exporters, [7
]. While the land use change associated with Unite States soy production occurred more than 25 years ago and so incurs no penalties in current greenhouse gas (GHG) emission assessments, expansion of soy production in Brazil is associated with deforestation [8
]. The major role of Brazilian deforestation to GHG emissions (Maciel et al., 2016) is now raising concerns among consumers, leading traders and governments to take measures to prevent deforestation [9
]. The carbon footprint (CF) of Brazilian soy used in animal feed depends not only on deforestation, but also the GHG emissions associated with transport to the importing country. The required transportation distance for soy used in European countries adds to the CF associated with soy use in European animal feed.
Meat for human consumption is derived from two types of animal: ruminant animals (primarily cattle and sheep) and non-ruminants (primarily fish, pigs and poultry). The ability of ruminants to digest fibre as an energy source and to utilise non-protein nitrogen to meet their amino acid requirements means that ruminant animals such as beef cattle are readily able to consume fibrous products that are not suitable for direct human consumption but their comparatively slow growth and methane gas outputs give a high carbon tariff to beef. In contrast, the high growth rates and extremely efficient feed conversion rate to usable meat of salmon and poultry give them a low carbon footprint but render them extremely sensitive to fluctuations in the quality of feed provided and the density of protein and energy in the feed, which limits the inclusion of many co-products. Each year, more than 30 MT of soybean meal is imported into the EU for inclusion in animal feed due to its high protein content, balance of amino acids and low levels of residual antinutritional factors [7
]. Poultry as a whole account for most soy use in the EU [10
], but production of soy beans in Europe is limited. Soy has a low yield and long growing season in the European climate and soil, so production cannot compete with the more efficient growth in countries such as Brazil [11
]. Soy use often does not fit sustainability objectives [12
] particularly as widespread deforestation is common in soy production in many countries.
In order to reduce the use of soy in poultry and fish feed, there is a need to consider novel and alternative proteins associated with lower carbon footprint (CF). Use of some conventional proteins have been limited in the EU, either due to lack of supply [13
] or due to EU wide bans [14
]. Alongside the mounting pressures to reduce levels of soy used in animal feed, legislatures such as The Renewable Fuel Standard in the USA and The Renewable Transport Fuel Obligation in the UK have driven massive increases in bioethanol production from cereal (first generation bioethanol). In 2011, the estimated global production was around 113 billion litres [15
]. Production of bioethanol is a exogenous enzyme and fermentation-based technology using Saccharomyces cerevisiae yeast to produce ethanol and a residual mash co-product known as ‘whole stillage’ which is subsequently decanted into a fibrous wet portion and a liquid component with only around 60–85 g/kg dry matter [16
], ‘thin stillage’ that contains the majority of the yeast protein and soluble components. In traditional ethanol fermentation systems, the thin stillage is evaporated into a syrup, remixed with the wet grain and dried to form Distiller’s Dried Grains with Solubles (DDGS). The evaporative drying of the co-product is an energy-demanding, expensive necessity in order to remove all the “waste” material not required for the production of ethanol from the distillery which, if not removed, would congest the primary process of ethanol production.
DDGS is successfully used in ruminant feed [17
] but the high fibre content decreases feed intake and limits nutrient utilization in fast growing species such as pigs, salmon, turkey and broiler (meat-type) chicken [18
]. Therefore, the biorefining process associated with bioethanol production has been recently adapted to develop high protein, low fibre biorefinery co-products more suitable for non-ruminant meat species than DDGS [19
]. The aim of this study is to assess the nutritional viability of partially replacement of SBM with corn-fermented protein (CFP) in the feed of fast growing meat species and to determine the impact of SBM replacement with CFP on the carbon footprint associated with the feed for each species.
Previous studies theoretically modelling LCA have suggested that a CFP type product increases nitrogen excretion associated negative environmental impacts [26
], but this study showed that nitrogen utilization was significantly improved with CFP for both poultry studies studied and not affected in salmon. Therefore, although the CFP has higher total protein nitrogen than SBM, its improved digestibility mitigates the additional feed nitrogen and reduces excretion to a similar level to SBM. Beyond the positive environmental impact associated with this improved nutrient utilization, further quantifiable effects are incurred earlier in the meat production process; associated with production of the individual feed material. Agricultural land use (ALU) associated with feed material production substantially contributes to CF, so maintaining low ALU values is a key focus in low carbon meat production. In the case of CFP, the ALU comes almost entirely from the production of the cereal crop [26
]. However, with multiple product streams deriving from the fermentation process, this ALU tariff is spread across a number of co-products including as corn oil and bioethanol. Therefore, the calculated CF of diets including CFP are substantially reduced compared to diets relying on SBM as the main dietary protein source.
Use of soy as livestock feed outside the Americas incur a high CO2
cost relating to the long distance of transportation. In addition, South American soy production is associated with high level of deforestation, resulting in particularly high ALU tariffs derived from the additional land use change. Accordingly, decreasing the dependency on soy in livestock nutrition would reduce the negative consequences of soy production and transportation on the environment due to the large penalties associated with land use change. CFP is currently produced at 500 thousand tonnes per annum from six bioethanol plants in the USA, which will increase to an estimated 1 million tonnes a year by the end of 2023. CFP is a co-product with high protein content which is produced from bioethanol generation. Accordingly, it is expected to be a low-GHG replacement of soy in livestock nutrition. Furthermore, it is more cost-effective source of nutrients for livestock compared to conventional feedstuffs [27
The results of the current study show N retention of broilers fed diets containing 5% CFP in place of SBM, and 8% CFP in turkey diets was higher than the control; which conflicts with previous studies on traditional bioethanol co-product: DDGS. Ref. [28
] reported that increased manure production and manure N excretion was produced by broilers fed high-protein corn distillers dried grains. This negative effect may be due to the increase in dietary fibre and reduction in protein digestibility resulting from heat damage associated with DDGS production [30
]. However, the replacement of soy by CFP in the current study did not introduce sufficient fibre or heat-damaged protein to negatively impact on broiler performance or nitrogen retention. Furthermore, the high digestibility of CFP reduces N excretion in comparison to wholly SBM-based diets. This improvement in N retention of broilers fed 5% CFP would decrease the NH3 emission from broiler production, creating added value from 5% CFP inclusion beyond the quantified parameters reported in the current study. Interestingly, 10% dietary inclusion of CFP improved nitrogen retention of broilers, but also increased feed intake without a concurrent improvement in weight gain, so deleteriously effecting feed conversion ratio and therefore negatively impacting the economic viability of including 10% CFP in broiler diets. However, a 10% dietary inclusion of CFP provides a 19% reduction in CO2
output compared with the control diet on a basis of per kg growth, and a 22% reduction in CO2
emissions on the basis of kg of meat produced. This reduction is 11% (per kg meat) and 14% (per kg meat) for the 5% inclusion of CFP. Turkeys may be fed diets including to 8% CFP in place of SBM with no effect on performance but a reduction in GHG emissions of 14% compared to turkeys fed the control diet. Distillers dried grains with solubles were included in broilers (up to 12%) and Turkeys (up to 8% diets) without negative consequences on growth performance [30
]. Similarly to the poultry studies, the salmon study showed no improvement in growth related to dietary SBM replacement with FP, and, as with the broilers, the highest CFP level diet led to a small, negative effect on growth. This lack of improved growth response in salmon is surprising as previous studies show DDGS may totally replaces fish meal in fish diets when fishmeal is included at a level of 12% of the diet [31
]. The DDGS was used as a protein source in rainbow trout diet without negative effect on digestibility and growth [30
]. It has also been reported that DDGS can be used at levels up to 90% of winter diets for channel catfish without amino acids supplementation [32
]. In alignment with the poultry trials, inclusion of 10% CFP in salmon diets leads to a reduction in CO2
cost of one kg growth of almost 14% over the control diet.
In all three species assessed, the impacts on growth performance were limited but the positive impacts of including CFP in place of soy on the CF of each species diet were substantial. This initial evidence that partial CFP replacement of dietary soy reduces the carbon footprint of meat production justifies further in vivo studies directly assessing carbon cost of meat from fish and poultry fed CFP-containing diets as predictive modelling approaches (Tallentyre et al., 2018) provide conflicting results.
In all three species assessed, the impacts on growth performance were limited but the positive impacts of including CFP in place of soy on the CF of each species diet were substantial. This initial evidence that partial CFP replacement of dietary soy reduces the carbon footprint of meat production justifies further in vivo studies directly assessing carbon cost of meat from fish and poultry fed CFP-containing diets as predictive modelling approaches (Tallentyre et al., 2018) provide conflicting results. Inclusion of CFP in broiler, turkey and salmon diets at a rate of 5%, 8% and 10%, respectively improved nitrogen retention while decreasing GHG emissions. This indicates partial replacement of soy with CFP in the diets of fast-growing meat species would reduce the environmental impact of meat production without impacting on growth performance.
Successful circular economies rely on precise alignment of needs between producers and users. Cereal-based bioethanol plants have historically produced a secondary product of low and inconsistent nutrient value that has limited attraction as an animal feed material. The expansion of cereal-based bioethanol production raised initial concerns that the concurrent increased supply of the traditional co-product (DDGS) would exceed feed use potential [34
]. However, the reframing of bioethanol production into biorefining, where multiple product streams are empirically scrutinized and modelled for optimum plant design [35
], has revolutionized the sustainability of cereal-based bioethanol plants. The new engineering and plant design focus has been on optimizing the generation of high-quality protein from the bioethanol plants [36
]. The multiple-species evaluation of CFP reported here shows that the biorefinery approach has created a protein product aligned to the needs of very high-volume users: salmon and poultry meat producers. The economic impact on the bioethanol plants pivoting to a biorefinery approach with multiple high value streams was particularly apparent as demand for transport fuel decreased during the early phase COVID-19 pandemic [37
]. The environmental impact of partially replacing soy with a biorefinery product (CFP) in the diet of salmon and poultry has been clearly demonstrated in the reported studies. This shows that the development of circular economies is not only an effective way to reduce the livestock and poultry pollution, but may also be used to improve the utilization efficiency of resources and support environmental protection, thereby allowing meat production to simultaneously supporting a number of UN SDGs without concurrent detriment to others.