Antibiotic Use In Pigs
Later weaning of piglets, as practiced in Sweden and in organic farming, leads to much lower antibiotic use. Rearing pigs outdoors, or in “enriched” indoor systems with lower stocking densities, can reduce diseases that require antibiotic use.
The information below has been taken from a new report from the Alliance to Save Our Antibiotics. You can find the full report here.
In the UK, and in many other countries, antibiotic use is by far the highest in pigs. The British pig industry has, however, begun to significantly reduce its antibiotic use in the last couple of years in response to public and regulatory pressure. In 2016, use was cut by 34% from 278 mg of active ingredient per kg of Population Correction Unit (PCU – the European unit measuring the size of livestock population) to 183 mg/kg . This, however, remains over three times higher than the government’s target of 50 mg/kg for farm antibiotic use .
This UK level of use also still compares poorly to the small number of other countries which have data on antibiotic use by species, particularly when compared with Sweden, where pig farming is significantly less intensive, see Table 1 (page 8 of report). However, other EU countries, like Spain and Italy, that don’t have species-specific data are likely to have much higher use in their pigs, since their use across all species is over 350 mg/kg of PCU.
RUMA and the National Pig Association have recently set a target of reducing antibiotic use in pigs to 99 mg/kg by 2020, which would mean that use in 2020 would remain twice as high as in Denmark and the Netherlands and over 6 times as high as in Sweden.
Some of the reductions in use so far appear to have been achieved by relying on alternative treatments to antibiotics. A key alternative that is being used in piglets is zinc oxide, which is added to piglet feed at medicinal doses to control post-weaning diarrhoea . Post-weaning diarrhoea is a major cause of antibiotic use in the pig industry (see below). According the NPA, zinc oxide, which also has a growth-promoting effect, is now being used in 70-90% of piglets in the UK, which is contributing to reductions being made to antibiotic use .
However, based on advice from the European Medicines Agency, the European Commission has decided to give Member States five years to withdraw all zinc oxide oral veterinary medicines due to concerns that it is toxic to plants and aquatic organisms and, because it is not biodegradable, it will accumulate in the environment. The European Medicine Agency also pointed to evidence that the use of zinc oxide may select for antibiotic-resistant organisms, although it wasn’t able to quantify this risk. Nevertheless, several studies
have found that the use of zinc in feed can increase the incidence of antibiotic-resistant E. coli and of MRSA in piglets , , .
With zinc oxide due to banned, and as the Veterinary Medicines Directorate plans to implement the ban by giving the full five years for the transition , the National Pig Association (NPA) is concerned that this may lead to antibiotic use increasing again , .
Another possible treatment that is sometimes used to prevent post-weaning diarrhoea in piglets is the inclusion of porcine blood plasma in the feed, as the antibodies in the blood help prevent bacterial infection20. Porcine blood plasma is permitted in many countries around the world, including in the EU  and the UK , but UK Red Tractor Standards for pigs do not allow it  and the NPA says that more than 92% of pigs in the UK are not fed blood products .
With the upcoming ban on zinc oxide, there may be pressure on Red Tractor to lift the ban on porcine blood plasma. However, the use of porcine blood plasma has already been linked with the spread of the highly-virulent Porcine Epidemic Diarrhoea (PED) virus from the United States to Canada in 2014 . PED is now present in Europe, although the strain is perhaps slightly less virulent .
The possibility of spreading of the PED virus, and perhaps other viruses, and maybe also Clostridium difficile spores, via blood plasma should be a warning to not reintroduce the practice of feeding porcine blood to pigs.
So if neither zinc oxide or blood plasma are part of the long-term solution, then as increasing antibiotic use will not be acceptable, the industry may need to consider examining weaning practices which are at the root of so many of the disease problems.
Later weaning helps lower antibiotic use in organic and other less intensive systems
Pigs in intensive, indoor systems can receive antibiotic treatment at each stage of their lives until slaughter, usually at under 6 months old. But it is at weaning, when piglets are often mixed with other piglets, and develop post-weaning diarrhoea due to stress and dietary change, when antibiotic treatment is at its highest. In some cases, even antibiotics that are classified as critically important in human medicine are used to control post-weaning diarrhoea .
However, several pieces of evidence which have been published in recent years show that the extent of antibiotic use at weaning can vary hugely, depending on the farming system and husbandry used.
In Denmark, antibiotic-use data is collected from all pig farms. The Danish data shows that antibiotic use in organic systems is ten times lower, and at weaning time it is 20 times lower, see Table 2 (page 9 of report). It is worth noting that, for the organic pigs, unlike the non-organic pigs, there is no sudden increase in antibiotic use at weaning time. This is probably because organic piglets cannot be weaned before 40 days of age, whereas in non-organic farming, they can be weaned from 21 days, which means that organic piglets have more developed gut flora at weaning.
Later weaning can also be of benefit in indoor, nonorganic systems. A study comparing antibiotic use on 227 pig farms in four EU countries found that use in Sweden was nearly seven times lower than in France, and use in Belgium and Germany was even higher than in France . Most of the difference in use occurred in weaners: as with organic pigs in Denmark, there was no sudden increase in antibiotic use in Swedish pigs at weaning time, and in fact use decreased. By contrast, in the three other countries, antibiotic use increased sharply at weaning, so that piglets received 20 to 30 times more antibiotics than they did in Sweden, see Table 3 (page 10 of report).
The most likely explanation for the difference was the later weaning of piglets in Sweden where the median age of weaning was 35 days, whereas in France, Belgium and Germany it was between 22 and 25 days.
According to industry data, the average weaning age in the UK and the EU is around 26 or 27 days . In order to minimise problems with post-weaning diarrhoea, moves to a later weaning age urgently need to be considered by the industry.
Lack of data on antibiotic use by farming system
There is still a significant lack of usage data which compares antibiotic use in different systems such as conventional intensive, free-range and organic production.
As mentioned above, the BPC now collects annual usage data from all of its members. However, none of this is published by farming system. Similarly, as discussed elsewhere in this report, several supermarkets have begun collecting usage data from their poultry farms, but none so far have committed to publishing it by system, even though the way the data is collected would almost certainly enable such comparisons to be made.
A small comparative study, carried out by Defra on UK pig and poultry farms, found much lower levels of use on organic poultry farms, see Figure 1 (page 11 of report).
Organic production differs from conventional production in many respects, several of which are very likely to have an impact on antibiotic use . These include stocking densities, access to the outdoors and the bird genetics, including in particular their growth rate.
Free-range production stands in between organic and intensive with respect to stocking densities and growth rate, and it is therefore very likely that antibiotic use in free-range production is somewhere between use in organic and use in intensive production.
Straw and “enriched housing”
According to a recent report by EFSA and the EMA, barren environments may result in behavioural abnormalities, such as tail biting and aggression . Pigs housed in straw-based systems generally have fewer injuries and feet problems than those kept on slatted floors  and straw bedding has also been reported to reduce gastric ulcers and lung damage , , . EFSA and the EMA point out that Swiss ”animalfriendly” farms (multiple areas, straw bedding, access to outdoor facilities) used less group-based antimicrobial treatments than control farms with slatted floors .
The Porcine Reproductive and Respiratory Virus (PRRSV) has been a major cause of increased antibiotic use, and of economic loss, in the pig industry as it increases pigs’ susceptibility to many bacterial infections . A recent Dutch study found that pigs in larger, enriched pens (straw, peat, wood shavings) were less susceptible to co-infection by PRRSV and Actinobacillus pleuropneumoniae (a cause of respiratory disease in pigs). The scientists said that “enriched-housed pigs showed a remarkably reduced impact of infection andwere less prone to develop clinical signs of disease”. They suggested that diminishing chronic stress in pigs could help reduce antibiotic use .
Although there is limited data, farming systems which require that pigs have outdoor access, such as organic farming or Swiss “animal friendly” farming, appear to have significantly reduced antibiotic use. It is known that organically farmed pigs have much lower antibiotic use, as Danish data and research by Defra scientists in the UK has shown, see Table 2 and Figure 1 (pages 9 and 11 of report).
However, organic production also differs from conventional production in terms of feed used, weaning age, stocking densities and other husbandry practices. Nevertheless, the EFSA and the EMA state in their report that access to outdoors is one of the practices used in alternative farming systems that “may also be used in other systems to reduce the need for antimicrobial use” .
Apart from reducing the likelihood of disease transmission between animals (“internal biosecurity”), a reason why outdoor rearing may reduce the need for antibiotics is that it appears to alter the gut microflora compared with indoor housed pigs. A British study compared the gut bacteria from genetically-related piglets raised outdoors and indoors. It found that the piglets reared from sows kept outdoors had much higher levels of the beneficial Lactobacilli bacteria. In contrast, piglets from sows housed indoors, whether receiving antibiotics or not, had higher numbers of clostridia and other potentially pathogenic bacteria , , . See Figure 2 (page 12 of report).
The scientists said “Rural, outdoor environments support the establishment of a natural microbiota dominated bylactobacilli and containing low numbers of potentially pathogenic bacteria and this may be an important factor in maintaining mucosal immune homeostasis and limiting excessive inflammatory responses in the gut”. A healthy gut is also likely to help reduce the need for antibiotics.
A key indicator of performance used in the pig industry is the number of piglets reared per sow per year. The average in the UK is now over 26 piglets, with the top 10% producing over 30 per sow . Selective breeding has led to ever greater litter sizes. Some super-prolific sows are now producing in excess of 17 piglets born alive per litter , , meaning that the number of piglets born can even exceed the number of teats the sow has , .
A scientific review by scientists from Scotland, Denmark and Norway found that large litter size is associated with increased piglet mortality, low birth weight, teat competition and increased likelihood that piglets will not get access to adequate milk. The scientists said that long-term effects on the piglets could include impaired gut function and immune function. There were also likely consequences for the health of the sow, such as udder damage45. A Swedish study found that large litter size has also been found to shorten the sow’s productive life, reducing her ability to produce more than 4 litters, as these highly productive sows have more udder and lameness problems .
Very large litter size may also mean that early weaning is necessary, in order to avoid the sow losing too much condition.
Breeding for more robust sows that have a more manageable number of piglets should be encouraged to reduce reliance on antibiotics. Outdoor systems, for example, breed for maternal traits in sows to reduce the need for intervention at farrowing, and have lower piglet numbers per litter , .
This information has been taken from a new report from the Alliance to Save Our Antibiotics. You can find the full report here.
For references, please see report.