Context

This post was written as a research project investigating whether it would be net positive for animals to pursue an intervention looking to reduce or eliminate antibiotic use in farmed animals. 

Many thanks to Vicky Cox, Cecilia Tilli, Phil Brooke, and Cóilín Nunan for their help and contributions. 

Antibiotic resistance in farmed animals

Executive summary

Reducing antibiotic use in farms is very likely to be net positive for humans. However, it is not clear whether it would be net positive for animals. If farmers stop using antibiotics, animals might suffer from more disease and worse welfare. This effect might be mitigated by the fact that (i) farmers can replace antibiotics with substitutes such as probiotics, prebiotics, and essential oils, which also prevent disease, and (ii) farmers might be motivated to make adaptations to farming practices which prevent disease and also benefit animal welfare, such as lowering stocking density, reducing stress, and monitoring disease more closely. It is not obvious how likely it is that farmers will take these disease-mitigating measures, but since high disease rates increase mortality, decrease carcass profitability, and could cause reputational damage, it is plausible that they will be motivated to do so. Alternatively, animal advocates could take the 'holistic strategy' of promoting welfare measures which also tend to cause reduced antibiotic use. Tentatively, I take the view that eliminating antibiotic use on a farm would not lead to worse lives for those animals.

Eliminating antibiotics might also be expensive for producers, and because of this, it could increase the price of animal products in the short term, which would be good for animals. The literature weakly supports the view that meat prices will increase following an antibiotic ban. However, there is also some support for the view that price will increase differentially for smaller and larger animals, which lands us with the small animal replacement problem. This problem could be avoided by the approach taken to the intervention, e.g. a corporate campaign targeting only small animals.

1. The problem

Antibiotics are used on farmed animals. They are used to treat disease (therapeutic use), to prevent disease (subtherapeutic or prophylactic use), and to promote animal growth (growth promotion use). In the US 70% of antibiotics (by weight) are used on non-humans, and figures are similar globally. Antibiotic use selects for bacteria which are resistant to that antibiotic, and therefore promotes the development and proliferation of antibiotic resistant bacteria. This leads to the spread of antibiotic resistant disease, which may be hard to treat.

It should be noted that antibiotic use by weight does not indicate that 70% of antibiotic resistant disease is due to antibiotic use on farms; resistant bacteria must transfer from farmed animals to humans, and it is currently very unclear how efficiently this transfer can occur. But it is at least evident that some proportion of antibiotic resistant disease is caused this way.

The most apocalyptic predictions suggest that antibiotic misuse means that humans will return to pre-antibiotic levels of mortality and morbidity. So we might expect that reducing antibiotic use in farming could have a large impact on public health.

2. Potential models for a solution

1. We could pursue a ban on antibiotic use on farmed animals:

• (i) total ban (incl. therapeutic use)
• (ii) ban on subtherapeutic use
• (iii) ban on growth promotion use
• NB. (ii) and (iii) are already in force in some countries e.g. EU and UK, but no country has a total ban.
• (iv) different levels of ban for antibiotics of different levels of importance for human medicine (e.g. total ban for Highest Priority Critically Important Antimicrobials, subtherapeutic ban for others, etc.)

2. We could pursue tax incentives for eliminating antibiotic use.

3. We could operate a corporate campaign demanding that companies eliminate antibiotics in their supply chain.

4. We could work with farmers to help them eliminate antibiotics on their farms.

5. We could promote animal welfare measures which tend to make farmers reduce antibiotic use (e.g. Dutch slower-growing chickens and delayed piglet weaning). 

6. We could pursue model 5 alongside some combination of 1-4 (the 'holistic strategy'; see section 4).

I’m not sure which of these is the most promising. I am fairly confident that a total ban would be net negative for animals because it would mean that some diagnosed diseases might have to go untreated. This view was supported by Phil Brooke of Compassion in World Farming. A corporate campaign can target one particular industry, which might have advantages if we consider the small animal replacement problem (see section 8).

3. Effect on animal welfare

Having fewer antibiotic resistant diseases benefits humans, but we can also expect it to benefit animals. Diseases animals get can be antibiotic resistant too. Cóilín Nunan of the Alliance to Save Our Antibiotics gives an example: 'On some intensive pig farms strains of a disease called swine dysentery have emerged which are resistant to all available antibiotics and are therefore untreatable. As a result all the pigs on the farm have had to be culled.'

A potential concern, however, is that because antibiotics are used to prevent and treat disease, reducing or eliminating antibiotic use would lead to animals having worse lives overall, because they would suffer from more disease. If this is the case, reducing antibiotic use should not be recommended as an intervention to help animals, because it would be net negative for animals.

However, it might not be the case that there is an overall decrease in animal welfare following reduced antibiotic use. There are still incentives for farmers to prevent disease by means other than antibiotics. Here are three reasons why farmers can’t let disease totally run rampant without mitigating it at all:

1) lowered profits due to mortality and carcass contamination from disease

2) animal welfare laws and/or animal welfare certifications

3) public health concerns and reputation damage from e.g. Salmonella, E. coli

I’m not sure how strong these incentives would be; according to Phil Brooke, 1 is the key incentive. 2 and 3 seem less strong, and depend on the country we are talking about. It may be the case that these incentives force farmers to do something to mitigate disease. Whether we think this is likely will greatly affect whether this intervention is net positive for animals.

There are two broad categories of things farmers might do to mitigate disease:

1. Welfare adaptations: Farmers could take steps that overall improve animal welfare. This is because a lot of things which happen to align with animal welfare goals also decrease the incidence and spread of disease; for example, reducing stress, decreasing stocking density, and improving hygiene. So these animals’ lives would be better overall.
2. Antibiotic substitutes: Farmers might use different methods to treat and prevent disease instead of antibiotics, which might be just as effective. So we would see no increase in incidence of disease, making these animals’ lives neither better nor worse overall.

4. Welfare adaptations

Compassion in World Farming (CIWF) has a guide on how farmers can adopt an ‘Antibiotic Stewardship Programme’ to reduce or eliminate antibiotic use. They list welfare adaptations farmers can make to reduce disease incidence following elimination of antibiotic use:

• Lowering stocking density
• Using more robust breeds (e.g. slower growing broiler breeds)
• Good environment
• Disease surveillance
• Good diet
• Hygiene
• Biosecurity
• Well-managed regrouping & mixing
• Good breeding
• Decreasing stress
• Avoiding routine mutilations (castration, tail docking, tooth clipping)
• Avoiding social isolation (e.g. dairy calves, sow stalls)
• Greater space allowance
• Outdoor access (esp. pasture-raising)

These types of change seem robustly good for animal welfare (indeed some are the same changes animal advocates campaign for!), and, although a detailed investigation into whether they prevent disease was not conducted, it appears to be consensus that either these adaptations would be as effective as antibiotics at preventing disease or the welfare gain from these adaptations would outweigh the modest increase in disease we might see.

It seems convenient that the effects of preventing disease and increasing welfare align in this way. It’s possible that there are some ways of mitigating disease spread which are worse for animal welfare; two examples are (i) vaccinations in fish - they prevent disease, but seem very stressful, and (ii) it is speculatively possible that larger farms have better biosecurity, so elimination of antibiotics might lead to integration of smaller farms. I did not however find any evidence of measures like this being taken, nor have reason to suppose they outweigh welfare-positive adaptations.

The most important consideration for welfare adaptations is whether farmers would be motivated to adopt them, without advocates specifically campaigning for them to do so (i.e. models 1-4 in section 1). I remain very uncertain on this issue, but tentatively think it is likely that profit incentives might make farmers make some adaptations. This is probably much more true in larger animals, in whom disease and mortality is more costly, since the market price per animal is higher. See also below (section 6) on limited evidence of welfare reforms following antibiotic elimination in industry.

If we think it is probable that farmers will not adopt welfare adaptations without pressure, then models 5 and 6 look more promising, as they are targeted specifically at securing welfare reforms. Phil Brook and Cóilín Nunan were both of the opinion that model 6, the 'holistic strategy', was the best option, stating that we must pursue bans on subtherapeutic and growth promoting use as well as advocating for welfare reforms. 

Intuitively, my view is that pursuing a single strategy directed explicitly at reducing antibiotic use would be more cost-effective on the margin, but I did not attempt to substantiate this as part of this project. I would be very interested in a more thorough look at this question. 

5. Antibiotic substitutes

Substitutes are relatively new and as such there are some open questions about the mechanism by which they prevent disease and their efficacy. See this piece for a more detailed look at antibiotic substitutes in extant literature.

Probiotics - available commercially & the most popular alternative currently used in industry.

• Work via ‘competitive exclusion’. Application is painless - applied via spray or drinking water
• CE preparations have been used in Finland since 1976 - now in ~90% of birds in Finland.

Prebiotics - increase gut health by stimulating harmless bacteria

Essential Oils - seem to combat Salmonella, and have antimicrobial properties in vitro.

Efficacy of these alternatives

• ‘Some of the replacement products such as organic acids, essential oils, herbs, probiotics, and prebiotics have been found to be variably effective to control these pathogens, but none of these alternatives has been proven as efficient as [antibiotics] in maintaining high production yields and controlling necrotic enteritis.’ (source)
• ‘To date, there are no reports on the effect of a combination of these products on economic and health conditions in commercial field trials’ (ibid.)

6. Current industry practices

This section is focused on chicken production in the US, because there is more evidence available in this area. A number of prominent chicken producers sell their meat with the label ‘No Antibiotics Ever’, and charge extra for this than ‘conventional’ equivalents. I looked for evidence that producers (i) were using antibiotic substitutes, (ii) had seen a change in incidence or severity of disease, and (iii) had made welfare adaptations.

(i) Perdue - eliminated subtherapeutic antibiotic use as of Oct 2016

Substitutes: Uses an undisclosed probiotic and oregano [essential oil?] (source)

Adaptations: Reduces stress by turning lights off for 4hrs per night (ibid.)

In 2018-2020, ‘Perdue Farms achieved a Tier 2 ranking from the Business Benchmark on Farm Animal Welfare (BBFAW) for the company’s animal welfare protocols.’

• The methodology report of BBFAW suggests that it is a genuine measure of animal welfare, and it’s promising evidence because it’s independent of Perdue. BBFAW does not mention disease incidence as a criterion for assessment, so Perdue’s BBFAW ranking gives us some evidence that eliminating antibiotics has not changed their chickens’ welfare, but no clear evidence on disease.

Perdue’s 2019 animal care report is (obviously) very positive about what they’ve achieved and how good their chickens’ welfare is, etc.

• Gives nothing specific on disease incidence, but ‘Improved bird health leading to a drier environment’ is noted as a contributing factor in decreasing the instance of foot pad dermatitis in their chickens. Speculatively, this could be because incidence of enteritis has been reduced (since enteritis makes litter wet).

(ii) Tyson - eliminated all antibiotic use from 2018

Substitutes: probiotics and essential oils (thyme, oregano, yucca, and peppers)

Adaptations: ‘We've redesigned our chicken's housing to give them plenty of room to roam.’ (source - Tyson’s website) ‘Through sanitation and better rearing practises, we can keep our birds healthy without antibiotics’ (source - a Tyson PR video)

However, we probably shouldn’t take this very seriously, as it’s PR from Tyson itself.

This page suggests a year-on-year improvement in animal welfare, including Acceptable Paw Scores of 78.0% in 2018, and 81.0% in 2019. Lower incidence of FPD could, as above, be used as an indicator that enteritis has also decreased.

However, this article notes that Tyson has a history of lying about antibiotic use on its farms.

(iii) Pilgrim’s Pride - working to reduce antibiotic use (unclear date/progress)

‘As part of our long-standing commitment to safeguard the welfare of our chickens, we treat all sick animals with antibiotics, if necessary, and then remove them from our antibiotic-free/NAE and organic programs. We will never allow a sick animal to suffer.’

• This is couched in PR language, but does at least suggest that antibiotic-free commitments do not incentivise producers to allow disease to run rampant.

7. Effect on price of animal products

Quite separately to the other considerations, reducing antibiotic use could end up being good for animals if it increased the price of animal products (and thus decreased demand, leading to fewer animals raised and killed for food). It is somewhat unclear whether this would happen, but I am overall quite confident that we would see at least a short term increase in price of meat following an antibiotic ban. The following is a non-exhaustive review of the literature on this topic.

It’s also possible that eliminating antibiotics could actually net increase demand for meat if consumers think that antibiotic-free meat is better/healthier/more natural.

• Three studies mention the possibility of increased demand; one thinks increased demand would more than compensate for the costs of increased production following a ban, another estimates that it would exactly offset the increased cost, and a third thinks we should assume no increase in demand. It’s therefore unclear what to conclude on this issue.

8. Price and the small animal replacement problem

If replacing antibiotics raises the price of meat, there is a further question whether the price of different meats rise differentially, and if so, whether the cost of small animals like chicken or fish might rise less than the cost of larger animals like cows. If that were to happen, we would run into the small animal replacement problem (SARP).

There is only one study which estimates the relative price change for different meat industries following an antibiotic ban, which does indeed suggest that chicken would increase in price less than beef and pork. This piece suggests that the reason for this is chickens’ shorter life cycles, so changes are more easily tested and adapted to.

If that’s right, then we should be less confident that a ban across industries would be net positive for animals, but we could nevertheless sidestep SARP by pursuing a corporate campaign targeting chickens only. This might make sense, given that this is the industry which has seen the most success eliminating antibiotics so far, and consumer demand appears to be there, given the commercial success of ‘No Antibiotics Ever’ labels.

One weakness of this approach is that I am not sure whether we could ask for a commitment to no subtherapeutic antibiotic use - would this be easily communicable, would it incite consumer pressure, and would it be an appropriate virtue signal for the corporation? Perdue and Tyson’s ‘No Antibiotics Ever’ label is much more categorical and obvious than ‘no subtherapeutic/prophylactic antibiotics used’ and looks better on a label or a menu. This might be able to be mitigated by the right framing of the campaign - e.g. ‘Responsible antibiotic use’ or ‘Antibiotic Stewardship’ (this latter is used by CIWF).

Conclusion

I tentatively support the view that an intervention using at least one of the strategies I have outlined would be net positive for animals, and that animal advocates should be optimistic about pursuing an intervention in this area.

My opinion would be changed if I found:

• Evidence that farmers do not make welfare adaptations following elimination of antibiotic use
• Stronger evidence that antibiotic substitutes such as prebiotics, probiotics, and essential oils are less effective than antibiotics at preventing disease
• Evidence that eliminating antibiotics lowers the price of meat
• Stronger evidence that eliminating antibiotics raises demand for meat
• Reasons to think that a corporate campaign in this area would not be viable