Boar taint

Boar taint is an odour or flavour, offensive to some people, which may be evident during the cooking or eating of pork or pork products. Find out why high levels of skatole and/or androstenone can taint the meat, and what can be done to avoid it.

What is androstenone?

  • Sex pheromone – its production is directly influenced by the activity of the testes; it increases dramatically as the pig reaches puberty
  • It can be measured to predict the presence of boar taint in fat tissues as it is fat-soluble
  • It has a ‘urine-like’ and ‘perspiration’ odour
  • Androstenone levels are enhanced by skatole levels

Androstenone production is positively related to age/weight, with the development of sexual maturity as boars get older/heavier. Optimising health and nutrition is important to ensure rapid growth and to achieve the target weight at a younger age. However, the correlation between carcase weight and androstenone production is low.

In terms of finishing weights, an AHDB-funded project showed that there were no significant differences in taint compound levels between 90 and 110 kg carcase weight groups (males), indicating that pigs can still be finished at these higher weights without developing boar taint.

What is skatole?

  • Of dietary origin and a by-product from the microbial fermentation of tryptophan (an essential amino acid) in the pig’s gut
  • It can be found in meat from boars, gilts and castrates, but levels are usually highest in boars
  • Fat- and water-soluble, so it is a useful predictor of boar taint levels in both fat and lean meat
  • ‘Musk-like’ and ‘faecal-like’ odour

Why is boar taint a problem?

The presence of boar taint is estimated to be in 1 in 10 males, but this may vary depending on the breed and the age. To avoid consumer dissatisfaction, the following levels should not be exceeded:

  • 5–1 ppm for androstenone
  • 2–0.25 ppm for skatole

Consumers in different countries often react differently to boar taint, as do male and female consumers. The British are generally less critical of pork containing high levels of boar taint than other consumers across Europe, while consumers in Asia, Africa and Latin America are particularly sensitive to androstenone. Females are also typically more sensitive to it.

In some countries, castration is carried out to avoid boar taint, but animal welfare concerns led to the 2018 EU voluntary ban. Routine castration is not carried out in the UK, especially as assurance schemes do not permit castrated animals to enter the market. Instead, males are slaughtered at a lighter weight, as it is believed that increasing slaughter weight leads to greater sexual maturity, causing greater androstenone levels. The level of skatole also increases with sexual maturity. It has also been suggested that although both androstenone and skatole are positively correlated with carcase weight and age, the correlations are not very high and slaughtering pigs at a low weight, with the intention to reduce boar taint, is not always effective.

Control of boar taint

Pen hygiene is important in terms of skatole levels as partial reabsorption can occur through the skin. Therefore, boars kept on heavily soiled concrete floors will have increased levels of skatole in comparison with those reared on clean slatted floor/concrete. Reingestion of faeces will also contribute to skatole levels.

Inadequate ventilation will result in pigs choosing to lie in the moister areas of the pen – the dunging area – resulting in absorption of skatole through the skin. Check that the ventilation is adequate and keep fans clean and serviced. Find out more information on ventilating pig buildings.

Mixing pigs is often associated with fighting as the hierarchy is established. Competition for food also leads to greater levels of androstenone in the fat and plasma. Even in entire male groups, boar taint levels can be increased due to social stress caused by mounting behaviour and aggression.

  • Pellets – studies indicate increased skatole levels in pigs fed the same diet in pellets as compared with meal form
  • Protein – feeding excessive protein can increase the risk of high skatole levels. This can be avoided by practising phase feeding, which varies the level of protein through the animal’s growth
  • Dietary fibre – skatole levels can be reduced by increasing dietary fibre content, particularly types of fibre which the pig can readily ferment, e.g. dried sugar beet pulp. Consult a nutritionist to discuss cost-effective inclusion levels. Increasing the ratio of barley to wheat may also reduce skatole levels, as barley contains a higher level of fibre
  • Chicory – previous research has shown that feeding 9% chicory for two weeks before slaughter can be effective in reducing backfat skatole concentrations but not always reducing the perception of boar taint itself. Chicory is rich in inulin – a complex fibre which is not digested in the small intestine and is able to alter the patterns of microbial fermentation in the large intestine; this can consequently reduce the production of skatole
  • Raw potato starch – this source of feed is linked to less skatole production; as the quantity of raw potato starch increases, the level of skatole declines. This is due to a lower transit time, along with less skatole absorption in the large intestine

Levels of androstenone in fat are mostly affected by genetic factors controlling its production and excretion, as well as the degree of sexual maturity. Marker-assisted selection could enable the industry to remove males with high skatole or androstenone levels from the breeding pyramid and reduce the risk of boar taint developing in pork and pork products.

Studies have shown that both compounds have moderate to high values for heritability, with a positive genetic correlation between the two traits. The estimated heritability for androstenone is 0.25 to 0.88 and for skatole is 0.19 to 0.54. However, direct selection based on these traits could lead to unfavourable side effects in terms of reproductive performance and productivity. Instead, identifying a specific section of the DNA which affects these traits could lead to more effective selection (marker-assisted selection).

For many years, boar taint has been included as a breeding target of Topigs Norsvin. Boar taint has been reduced in their lines by over 50% over the past decade. In particular, the progeny from the Nador boar have even less boar taint. This breeding target is applied to both the dam and terminal sire line.  

Another method to control boar taint is to select the sex of the piglet before birth using sorting. This is based on the sex chromosomes and artificial insemination. Although this method has been successfully used in cattle breeding, it is still under research and no economic or practical solution exists in pig production yet.

This is achieved by a vaccine, Improvac, which is administered intramuscularly (2 ml) from 8 weeks of age. The injection should be given twice, with a minimum of 4 weeks apart between doses, and the second dose given 4 to 6 weeks before slaughter.

If slaughter occurs more than 10 weeks after the second dose, a third dose should be given 4 to 6 weeks before slaughter. This stimulates the pig’s own immune system to temporarily block the function of the testes, reducing the production and accumulation levels of boar-taint-causing compounds. As well as minimising the risk of boar taint, producers can capture the performance, health and carcase quality benefits of rearing male pigs as entire boars for most of the finishing period.

AHDB (formerly BPEX when the project started) supported Kelly Westmacott’s PhD project ran from 2014 to 2018 and covered ‘development of novel technology for boar taint detection to assist with the production of taint-free pork ’. This is the first ‘on the line’ device for boar-taint detection in fat tissues and is rapid, portable and cost-effective. It will help safeguard against prime meat cuts containing boar taint from reaching the consumer. 

The Dutch programme ‘boars heading for 2018’  reports on the results of the project carried out over five years between 2009–2013 on stopping castration. Key findings from this report to control boar taint include:

  • Pen sizes of ≤ 10 boars
  • Housing < 5 years old
  • Prior to slaughter a fasting period of ≥ 6 hours