Livestock on leftovers will not save us, we have to reduce meat
Can it be done? Probably. Would it solve our problems? Not really.
In response to the issues created by Feed-food competition, Some now advocate for a "livestock on leftovers" approach. Intuitively, this strategy involves only feeding livestock crop residues and by-products that humans cannot eat, as well as uneaten human food.
Some version of this strategy is already widely applied informally across the world; it is common for ‘backyard livestock’ to be fed food scraps. It is less common in more intensive agricultural systems; in Europe it is illegal for animal agriculture to feed livestock with untreated human food waste. Livestock may only be fed by-products from food production (such as whey powder) or food that was produced but could not be sold for whatever reason (i.e. surplus production or defective). This is because of potential disease risks; it is thought to have caused the 2001 outbreak of Food and Mouth disease in the UK for example. Despite this, a 2018 survey found that over 75% of British pig farmers supported re-legalization, indicating that Livestock on leftovers may be quite popular among farmers.
There is clear potential for livestock on leftovers to provide a variety of benefits. One review explored the specific case of feeding farmed animals uneaten human food that would otherwise go to waste, specifically focusing on stale bakery products. They found that food safety for animals was generally satisfactory, but the effects of low fibre, sugary carbohydrates on livestock gut microbiomes were not well understood. They found that this method of feeding livestock this way could reduce greenhouse gas emissions as otherwise the food would go to landfill.
However, large scale assessments suggests that the benefits have substantial tradeoffs. A simulation by Shrader et al . found that for the world to produce enough food (and protein) in 2050 using a pure livestock on leftovers approach, global meat consumption would have to decrease 71% on current levels. Similarly, another simulation found that Nordic countries would have to cut meat consumption by 89% if no livestock were fed crops, or drastically increasing food imports. Considering that most of the world is increasing meat consumption, such a dramatic change seems unrealistic. Shrader et al., also noted that meat produced per animal decrease anywhere between 0-40%, as many leftovers are less calorie dense than the concentrated animal feed typical of industrial animal agriculture. Finally, they found that ruminants fed by grazing and leftovers had higher greenhouse gas emissions per animal, though this was of course completely negated by reduced emissions from dramatic meat reduction. Surprisingly, one analysis of multiple studies concluded that livestock on leftovers would free up 25% more arable land than if humanity did not eat any animal products at all (i.e. world veganism). This is because feeding livestock human-inedible food would convert inedible calories into edible ones, meaning that we would need to grow fewer crops, sparing land. Once again however Europe and America would have to reduce meat consumption by 60-70%, perhaps as high as 80% in order for Asia and Africa to increase their meat consumption. Whilst a Livestock on Leftovers approach could reduce food waste and would likely be safe for animals, the risk of greatly reduced yields and higher GHG per animal means that it would only be feasible if society was already in the process of making large reductions in meat consumption.
Estimates of how much protein could be provided range from 7 g/capita/day (van Kernebeek, 2016; Smil, 2014) to 31 g/capita/day (van Hal, 2019). the lower end estimates of this set of studies can be
assumed to be overly conservative for the UK. These are often based on global averages (7g, Smil, 2014; 9g, Schader, 2015) rather than European data (e.g., Roos, 2016, 2017; Elferink, 2008). Often the global studies assume tropic cattle, non-optimised breeds etc.
Van Hal
Van Hal et al’s upper estimate of 31g is based on a model that includes all available grassland (not just
marginal), by-products, and 35% of food waste used for animal feed. The modelled system supports 78% fewer pigs, 98% fewer laying hens but 9% more dairy cattle for the EU as a whole. In the model broilers and beef cattle are excluded entirely. For the UK specifically, the model suggests an optimal livestock population of 10 million pigs (twice as many as today) consuming mostly oilseed by-products
and food waste; and 3 million dairy cattle consuming mostly grass plus a small percentage of supplemental oilseed and cereal processing by-products.
Notes on this from WWF, 2022
- calls this "high and low opportunity cost feed"
- because the UK over-consumes calories and protein, a shift towards all livestock eating non-human food would still meet the UK's calorie and protein needs. we'd still meet the EAT Lancet.
- numbers of poultry would need to be reduced drastically, as low opportunity cost by-product feedstocks suited to the current production paradigm (such as the bakery waste used by Dutch firm Kipster) are limited. In the medium term, legal and technological developments to allow the processing of food waste by insects, producing a high-protein insect meal, could provide an additional feedstock. The first report in WWF UK’s Future of Feed series suggests that, with appropriate investment and policy support, insect meal could replace half a million tonnes, or around 20%, of soy in feed by 2050
- Ruminants, however, are the key to a system based on low opportunity cost feed. But cows produce most of the pollution in the UK. Animal agriculture is a big source of air pollution, as well as GHG
- They estimate that an optimistic scenario means we could produce 31g of animal protein per person per day, and EAT Lancet recommends 27g. Except that EAT Lancet recommends a 41% reduction in protein from meat.
- EAT-Lancet recommends the consumption of higher quantities of chicken meat (29% of ASF protein) compared to beef and pork (13%), but because low opportunity cost feeds are less suitable for poultry, an optimised LOC system would produce mainly dairy-beef, milk and pork
If the UK wanted to move to a LOL approach, A 2023 report finds we'd need to reduce meat by 80%!