Correction: Environmental impact of feeding plant-based vs. meat-based dry dog foods in the United Kingdom

Vegetarianism, veganism-encapsulated as following a 'plant-based' diet, is increasingly popular among consumers; for reasons of better health, not eating animals and, increasingly, for greater sustainability (Rothgerber, 2013;Ingenpaß et al., 2021). Increased population size has inevitably placed greater demands on the food chain, mitigated somewhat by increased production efficiencies. However, the environmental impact of the need for more food has generated increased greenhouse gas emissions, exacerbated deforestation, land degradation, biodiversity loss, freshwater depletion and increased pollution of soil and water sources (Pimentel and Pimentel, 2003;Reijnders and Soret, 2003;Westhoek et al., 2014;Poore and Nemecek, 2018;Humpenöder et al., 2022;Scarborough et al., 2023).In 2018, the global canine population was estimated at 471 million (Sivewright and Krueger, 2019). Feeding these omnivores a meat-based diet, even when accounting for the use of 'by-products' , generates considerable greenhouse gases (GHG). The potential for exchanging meat-for plant-based alternatives, when feeding companion animals, could therefore significantly reduce the environmental impact of pet food (Humpenöder et al., 2022). A number of previous studies have assessed different aspects of the environmental impact of pet foods (Swanson et al., 2013;Okin, 2017;Su and Martens, 2018a;Su and Martens, 2018;Martens et al., 2019;Alexander et al., 2020;Pedrinelli et al., 2022;Knight, 2023;Jarosch et al., 2024;Nicholles and Knight, 2025). The estimated environmental impact of manufacturing dog food in Brazil has been calculated to be 2.9-24.6% of the total carbon dioxide emissions of the country (Pedrinelli et al., 2022). In China, it was estimated that dogs fed commercially-produced pet food accounted for three-fold greater carbon emissions than dogs solely eating leftover, human-grade food (Su et al., 2018). In 2015, the GHG footprint of cats and dogs in China-in terms of food consumption-was estimated to be between 2.5 and 7.8% of the GHG footprint of the total population in China. Globally, estimates suggest that production of pet food, including use of by-products, requires 41-58 million hectares (mHa) of agricultural land, around twice the land area of the United Kingdom (24.9 mHa). Thus, it has been suggested that pet food production generates equivalent GHG emissions as some countries such as Mozambique or the Philippines (Alexander et al., 2020).Producing red meat for animal protein (e.g., beef and lamb) for human (or pet) consumption, registers, without doubt, the greatest impact on the environment in terms of land area, water use and GHG emissions. Growing plant-based protein generates a fraction of the environmental cost; indeed, even when comparing pea-protein producers with the highest carbon footprint (i.e., 0.8 kg CO 2 eq/100 g protein) vs. the lowest impact farm for lamb, beef or chicken production (12.0, 9.0 and 2.4 kg CO 2 eq/100 g protein, respectively), the difference remains stark, particularly when scaled-up globally (Poore and Nemecek, 2018;Ritchie, 2020). Although studies have investigated the reduced environmental impact of people adopting a plant-based dietary pattern, and the reduced impact of plant-based pet food consumption by companion animals, none have directly compared the environmental impact of meat vs. plant-based (vegetarian and vegan) dog food in the United Kingdom. Jarosch et al. (2024) estimated the environmental impact of wet, vegan dog food. However, wet foods are known to have a higher environmental impact than dry foods (Pedrinelli et al., 2022;Jarosch et al., 2024) and 50-70% of UK pet owners choose to feed dry kibble (Morelli et al., 2021;Pet Food Industry, 2023), either on its own or mixed with wet food. Previous studies evaluating the impact of pet food manufacturing in Japan (Su and Martens, 2018b) and China (Su et al., 2018) are not directly applicable to the United Kingdom given our variations in pet preferences and population, as well as access to different ingredients.In the current study, using validated methods to estimate the environmental footprint of pet food production, we calculate the environmental impact of feeding plant-based vs. other commonly fed animal-based diets in the United Kingdom (meatbeef, lamb, poultry; veterinary diets-semi-synthetic animalbased ingredients).The environmental impact of 31 adult dog foods commercially available in the United Kingdom, were calculated with regards to land use (m 2 /1000kcal), carbon dioxide equivalent (CO 2 eq(kg)/1,000 kcal), acidifying emissions (SO 2 eq(g)/1,000 kcal), eutrophying emissions (PO 4 3eq(g)/1,000 kcal) and freshwater withdrawal (L/1000 kcal). These were calculated using previously published values (Poore and Nemecek, 2018).31 complete dry dog food samples were acquired from supermarkets in the United Kingdom. Food was representative of 27 different brands. Any foods not labelled as 'complete' and for 'adults' were excluded. Veterinary diets were only chosen if they specifically claimed renal benefits. Purchased products were grouped according to their main protein source, as listed on their labels, as: "meatbased"-poultry (n = 7), lamb (n = 6) and beef (n = 6); "plantbased"-including vegan (n = 4) and vegetarian (n = 2) foods. In addition, n = 6 veterinary diets, specifically formulated for animals with renal problems were tested. Veterinary diets have a guaranteed analysis of composition on the label, are usually semi-synthetic with no specific main flavour, but are fed regularly in the United Kingdom and thus were included as a discrete category. Pork, rabbit and other meats were not included in the study as available products were limited. Results represent only single batch analysis.Across 31 foods, all 298 ingredients were reviewed, encompassing up to 33 individual ingredients. Most individual foods (27/31, 87%) included between 6 and 20 ingredients. All ingredient terms used were pre-defined (Pedrinelli et al., 2022). In summary, "meats" are considered "raw meat" unless specified on packaging and "meat meals" were considered cooked. "Animal protein hydrolysate" is reported as "chicken protein hydrolysate. " Vegetable percentages are provided by fresh weight where possible. "Animal fat" (where the animal is not specified) and "poultry gravy" have been reported as "poultry fat. " "Dehydrated poultry protein" has been reported as "poultry by-product meal. " Where "oils & fats" are listed, this is reported as "sunflower oil, unspecified. " "Salmon oil" and "fish oil" are both reported as "fish oil. " Rye and spelt are reported as "whole wheat. " Maize gluten has been reported as "corn gluten meal. " "Wheat" has been reported as "wheat gluten. " All varieties of wheat have the same impact values. Unless listed in the ingredients as "brown rice, " rice has been reported as "white rice, cooked. " Pasta is reported as "spaghetti. " All "potato protein" is reported as "potato starch. " Potato starch and cooked potato have the same impact values. Where label ingredients did not have an equivalent ingredient with pre-calculated impact value, these were excluded from the estimation. Excluded ingredients include, but were not limited to, glycerol, minerals, lupine, alfalfa, algae, botanicals, vegetable stock and chicory. In 30/31 foods, the first 4 ingredients, which is often the majority of the food composition, were always included in the estimation. One food listed "glycerol" as the third ingredient. Where "animal by-product" (ABP) is 10.3389/fsufs.2025.1633312 Frontiers in Sustainable Food Systems 03 frontiersin.org referred to, this includes, but is not limited to; hides, skins, hydrolysed protein, rendered fat, digest, milk by-products, eggs, fish products and bones (Gov.uk, 2019). Previously, ingredient weightings were based on the first five ingredients, each given a 20% weighting, or a 1.5 ratio in descending order of ingredient inclusion (e.g., 38.4% for the first ingredient, 25.6% for the second, 17.1% for the third; Okin, 2017;Alexander et al., 2020). In the present study, a modified ratio, based on the dietary group being analysed, provided a more accurate representation: ingredient percentages were taken from package ingredient lists, assuming a descending order of percentage incorporation (see Supplementary material). When proportions were undefined, an average percentage for the dietary group (e.g., meat-based, plantbased, or veterinary) was applied based on the ingredient's position in the list (e.g., fifth ingredient). In cases where ingredients were listed as a single percentage (e.g., "dried chicken and turkey 30%"), a 50:50 ratio was used (15% dried chicken, 15% dried turkey). Using this method, the total ingredient composition ranged from 39.29 to 120%, before being adjusted to 100% to ensure an equitable comparison between all foods.Life cycle assessments (LCA) are the current standard for assessing environmental impact, with many studies using some variation (Van Zanten, 2016;Yavor et al., 2020;Jarosch et al., 2024). Estimations of five environmental impact scores (per 1,000 kcal metabolisable energy [ME]) were calculated for all pet foods, including (1) land use (m 2 ) as shown below in Equation 1, (2) carbon dioxide equivalent (CO 2 eq), (3) acidifying sulphur dioxide (SO 2 ), (4) eutrophying phosphate (PO 4 3-) emissions and (5) freshwater withdrawal (L), with the only difference for additional calculations being the appropriate impact value (Pedrinelli et al., 2022) in place of "ingredient land use impact value" (Equation 1).Impact values represent a methodologically harmonised dataset of life cycle assessments (LCA) from 570 suitable studies: representing ~38,700 farms in 199 countries and producing ~90% of the global protein and calories (Pedrinelli et al., 2022). Over 1,000 post-farm processes were included in the production of these impact values, including processing, packaging, retail, transport and losses, up the point of consumer choice.Moisture content of dry foods is usually 5-8%, and in our experience of direct measurement is usually 4-6%. In this study, in order to provide estimates of GHG emissions per 1,000 kcal ME, with energy density estimated using Atwater criteria for all proximates on the label, then final values for environmental impact were determined considering ingredient percentage composition and the food moisture content. As an example, for each ingredient:x adj. factor: C/B where moisture adjustment factor (B) = 100/(100-A) [moisture % (A) was taken from label] and percentage of ingredient in formulation (C) was also taken from label. The sum of all ingredients in a food (up to 22) were calculated, they were summated to create a total for that food. Finally, a factor was applied to standardise all foods to a theoretical 100% inclusion rate (e.g., if individual ingredient percentages in a single food only totalled 94.5%, a factor of 1.058% (100/94.5) would be applied to each ingredient to achieve 100% and allow for comparison between different foods in our analysis).Taking the above calculations into account then environmental impact values were as follows, e.g., for Land use (Equation 1):Estimation of land use requirement for production of an individual pet food. % . 100 L impval x comp x adj factor     Σ        (1)where L.impval (land impact value), expressed in m 2 /1000 kcal, was previously calculated (Pedrinelli et al., 2022), %comp is the moisture-adjusted percent composition of individual ingredient in each food. The impact of all individual ingredients was summated, adjusted to 100% as described above. Similar equations were used to calculate carbon dioxide equivalent (Equation 2, kg CO 2 eq/1000 kcal in Supplementary material), acidifying emissions (Equation 3, g/1000 kcal SO 2 eq in Supplementary material), eutrophying emissions (Equation 4, g/1000 kcal PO 43-eq in Supplementary material) and freshwater withdrawal (Equation 5, L/1000 kcal in Supplementary material).Data were analysed using analysis of variance (ANOVA) for the fixed effect of the three diet-types (meat-based or plant-based, veterinary). To meet assumptions for analysis by ANOVA, all data were checked for a normal distribution of residuals and respective data were ) to analysis by or a suitable distribution was used (e.g., All such data were analysed using United and using United use (m 2 /1000 kcal), carbon dioxide equivalent CO 2 eq/1000 kcal), acidifying emissions kcal SO 2 eq), eutrophying emissions kcal PO 4 and freshwater withdrawal (L/1000 kcal) were calculated for each ingredient of food, These values were adjusted for the percentage of the food that the ingredient using listed and theoretical proportions (see and for for each food were then calculated per 1,000 kcal fed to account for in moisture content and energy density between foods. plant-based foods the lowest environmental impact scores for each estimated beef or lamb always the highest Veterinary foods, being were between these the labels, the average content of proximates and of plant-based foods were and vs. and Veterinary foods protein with higher inclusion and all foods, different ingredients of ingredients without suitable impact values to were assessed the 31 foods. third of ingredients were When comparing the ingredients of all foods, the ingredients were gluten in rice poultry wheat gluten and rice, chicken meat and potato and vegetable protein When the formulation into account (up to the ingredients were gluten poultry rice and and the meat-based foods were different ingredients, of which were The ingredients were poultry gluten and rice The 6 plant-based foods different ingredients, with an The ingredients were and gluten and average land use to lamb and beef dog foods were but was significantly greater than the land use to veterinary and plant-based foods = In this study, the average estimated land use to each dry dog food was 2 /1000 kcal for lamb, 2 /1000 kcal for 2 /1000 kcal for poultry and 2 /1000 kcal for Veterinary diets 2 /1000 kcal which was not different to poultry and plant-based foods. ingredients in the pet food greatest land use included lamb 2 /1000 kcal), meat and of 2 /1000 kcal) and beef 2 /1000 ingredients greatest land use in plant-based foods were such as protein 2 /1000 kcal) and cooked 2 /1000 agricultural production, greenhouse gases carbon and To all GHG emissions from dog food production, emissions were expressed as carbon dioxide (CO 2 in kg CO 2 eq/1000 kcal of food. foods the lowest GHG emissions kg CO 2 eq/1000 kcal) which were to poultry kg CO 2 eq/1000 kcal) and veterinary foods kg CO 2 eq/1000 In beef kg CO 2 eq/1000 kcal) was significantly higher than all other foods, including lamb kg CO 2 eq/1000 kcal) which was also significantly higher than with highest CO 2 eq impact values for meat-based foods included meat and CO 2 eq/1000 kcal), beef CO 2 eq/1000 kcal), beef CO 2 eq/1000 kcal), lamb CO 2 eq/1000 kcal) and protein CO 2 eq/1000 kcal). The highest impact values in plant-based ingredients were CO 2 eq/1000 kcal), CO 2 eq/1000 kcal), CO 2 eq/1000 kcal) and wheat gluten CO 2 eq/1000 emissions (PO 4 are a of the pollution of soil and from particularly as a and dioxide et al., 2022). emissions (SO 2 sulphur dioxide (SO 2 ), and from and other of the manufacturing animal which with water and to acidifying such as and in the before as and Soret, 2024). both plant-based food the lowest emissions, and beef the greatest eutrophying (PO 4 and acidifying (SO 2 values were between lamb, poultry and veterinary foods, as for lamb significantly greater emissions than plant-based foods = acidifying values for beef were Frontiers in Sustainable Food Systems frontiersin.org and that of lamb, veterinary and plant-based foods, eutrophying emissions were and freshwater calculations to the freshwater used in and in to the life cycle of pet food These water used for production and for direct use for 2025). diets the highest average freshwater withdrawal L/1000 kcal), by beef L/1000 kcal), veterinary foods L/1000 poultry L/1000 kcal) and plant-based foods L/1000 kcal). food significantly freshwater withdrawal than lamb or beef = with all estimates in an grouped only by food then lamb and foods significantly from all other The first difference in foods to the of land freshwater withdrawal and CO 2 eq production significantly to The difference in foods was by a of CO 2 eq SO 2 eq PO emissions plant-based and poultry foods environmental impact of study is the first to the environmental impact of commercially available meat-based and plant-based dry dog foods available on the UK with global that plant-based diets are the of land greenhouse gas emissions, and water use (Pedrinelli et al., 2022;Knight, In diets lamb or beef generated the highest environmental by veterinary and foods. These have when to the of a single as well as the UK pet population, or the dog is considered adult for on by the and and by the with some also and specific for each life provide dogs with appropriate to their at that point in In this study, the only adult dog food, and only be for this life The environmental impact of on ingredient composition, with between meat-based and plant-based 20 kg the popular dog in the United Kingdom with to requires g of food kcal) per Over this to kg of food diets a in These are by in the and et al., 2019). the greenhouse gas emissions by the plant-based, or lamb foods this would be equivalent to and between and per on a These values are to previously described et al., 2020). also significantly on the size of the and its energy and estimated that feeding a kg dog of meat-based food requires a would a and a this of dogs considerable to land from both human and food use as of the of environmental impact among different dog food land use estimates to including (up to per of land between and of such as (Poore and Nemecek, 2018). These more than but they the in land between animal-based and plant-based dog this study, plant-based diets an average of m 2 per 1,000 kcal, compared with 100 m 2 for beef and and the highest plant-based the current study of products a land impact, with the production million used globally in an area equivalent to and the UK However, plant-based foods and direct consumption to as more than of is to feed than direct human or pet consumption and 2020). In addition, meat protein production has been shown to have higher land requirement than production and Soret, chicken, often as a protein, also on and for both of which with the human food and diets to higher CO emissions than or veterinary These that of agricultural GHG emissions from soil to deforestation, and from (Pedrinelli et al., 2022). Although ingredients such as have for land their total emissions per of that pet dogs a environment to vegan diets could reduce total global GHG by many dogs around the fed animal-based diets are or in animal and thus this of is a pollution is of animal commonly used as a ingredient in pet food to and health, are often from phosphate the manufacturing which to of into water and Soret, are also present in which are applied to study plant-based diets phosphate and emissions than beef or lamb These emissions to and with on biodiversity et al., the agricultural phosphate (PO 4 3-) are into the soil and an of and et al., 2023), to the of of CO 2 , and water and and 2024). Food production is the single to global and freshwater around and of which is at the farm (Poore and Nemecek, 2018). significantly to of soil and water of to feeding plant-based at estimated impact value for all of foods fed a of an adult is compared to feeding to in countries around the with or more of global freshwater being used for and and lamb the water per 1,000 kcal, with plant-based diets using the and previously that water for production all other with wheat and among the The global water footprint of production in the was , with wheat up 15% of with a total water footprint are rice ) and However, water feed for of the water use (Pimentel and Pimentel, estimate the production of and was estimated to use L of water to kg of fresh dogs were fed which a impact on the environment (Su et al., 2018). However, the in of dog foods, which increasingly of the animal for human consumption, has of the meat-based protein sources analysed in this study were from meat than fresh of which are as animal as from the human food These are often considered a more than meat et al., 2023), and are that they reduce use of that be (Alexander et al., 2020). However, that the environmental of used in dog food be reported that not for human consumption more animals per of protein, compared to and that using in pet food be than using to and our meat and a was among the ingredients, with land use values of 2 , and emissions of kg per 1,000 kcal as and from with emissions from to to their water use for is of the water from feed and animal diets above plant-based in terms of freshwater some used in pet food could be for human or et al., sustainability The of using ingredients in pet food therefore be assessed the and of in other a food the of the land is to and of is used to production (Van Zanten, not only but considerable of used to a global population an food and the of a more food is (Van 2022), as well as the of and in food production et al., et al., 2019). that compared to a where for direct human consumption could up to of global could also provide around g of protein per animal consumption above this would to be to et al. this and that feeding animals on and food production by-products, than human could land use by and GHG emissions by these into pet food production with to sustainability without with human food In study, using and a pet food as its in et al., 2022). However, even pet owners food as this did not their as as the of the food. In to other available studies the to plant-based dog food, the current have previously shown that they be as complete as meat-based foods et al., impact values used in this study are at the point of (Pedrinelli et al., 2022) and only account for the production, manufacturing and distribution of the food. additional environmental of animal and packaging of previously (Swanson et al., et al., have not been accounted the environmental of ingredients is limited by data assumptions for In some our specific impact values, based on ingredients, which not represent current production as by Jarosch et al. values not with global are these the need for data to study the from previous in other the United Kingdom, feeding dog plant-based significantly a vs. feeding meat-based be that and of foods was the of this study and as such the food other than on the of Using animal in such of GHG emissions, not reduce the in environmental sustainability between plant-based foods. Although poultry and veterinary foods impact than with beef or lamb as the main ingredient, they than plant-based global food and pet pet food ingredients be in the