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Boar taint is a sensory defect of pork, which presents an odor/taste similar to urine, sweat, or feces and is mainly due to androstenone and skatole. The main strategy to reduce it is castration.
For several years, castration without anesthesia has been questioned in Europe and this has led to changes in the type of animals produced. Currently, some countries, such as Norway, Sweden, and Germany, produce mostly castrated animals using anesthesia, while France, Holland, and Belgium castrate using analgesia. Other countries, such as Italy, Poland, Romania, and Russia, produce castrated males without using anesthesia (Aluwé et al., 2020, Lin-Schilstra and Ingenbleek, 2021). For many years, the United Kingdom and Ireland have been producing basically entire males and in Spain, the proportion of entire males has increased in recent years, currently standing at 80-85% of males, although there are specific subpopulations in which the percentage of castrated males is very high.
Alternatives to surgical castration (with or without anesthesia) are the production of entire males or the immunocastration. Some countries such as Germany, France, Holland, and Belgium have introduced entire males in varying proportions. Likewise, immunocastration, widely used in countries such as Australia, New Zealand, and Latin America (Brazil, Mexico, Chile, Colombia, and Argentina), is only used in small proportions in Europe in Belgium, Germany, Norway, and Sweden (Weiler et al., 2021) and in female pigs in Spain.
Especially when producing entire males, it is important to apply on-farm strategies that help to reduce boar taint and, at the same time, to use systems in the slaughterhouse to detect it in the carcasses (Font-i-Furnols et al., 2020, Burgeon et al., 2021) and, thus, be able to identify those with anomalies and assign the carcass an appropriate destination (Škrlep et al., 2020).
On-farm strategies are mainly based around management, nutrition, and genetic selection (Bee et al., 2020, Borell et al., 2020, Larzul, 2021) and are more or less effective for one or both of the two compounds responsible for boar taint. In this regard, genetic selection is more effective in reducing androstenone, while nutritional strategies are more effective in reducing skatole, and animal management is effective in reducing both compounds.
At the slaughterhouse level, the methodologies/technologies used are the human nose to classify according to the level of boar taint on line or at line and the colorimetric method to determine skatole equivalents at line. In the near future, some slaughterhouses will implement a laser diode thermal desorption ion source for mass spectrometry (LDTD-MS/MS) to determine androstenone and skatole concentration at line.
Figure 1: On-line evaluation of the carcass and at-line evaluation of the fat using the human nose.
The human nose is the most commonly used method (Figure 1). It is used in some slaughterhouses in Belgium, Germany, Holland, France, and Spain. It consists of sensory evaluation of carcasses by trained panelists. The panelists smell the carcass fat, which is previously heated, generally with welding equipment and they classify it according to the level of perceived boar taint. It requires specific and continuous training of the panelists and it is important to know their sensitivity and specificity, in order to know the accuracy and precision of the panel (Mathur et al., 2012, Trautmann et al., 2014). This is used in several European slaughterhouses and requires a panel made up of several trained panelists that alternate to avoid fatigue and saturation and that allows more than one panelist on the line, if the line is fast, to alternate the carcasses to be evaluated.
The colorimetric method has been used in Danish slaughterhouses since the 1990s. It measures skatole equivalents and the value obtained is used in the payment the farmers receive for the carcasses.
It has recently been demonstrated that LDTD-MS/MS (Borggaard et al., 2017, Auger et al., 2018, Lund et al., 2021) may be the future for the evaluation of androstenone and skatole at line, as it is a fast and robust method, which allows the automation of sampling and analysis. This method is marketed by two companies and one of them has also developed the complete automation of the entire process, including sampling and sample pretreatment, allowing 360 samples/h to be evaluated (Font-i-Furnols et al., 2020; Borggaard et al., 2017). This method is going to be implemented in Danish slaughterhouses soon. An important point in grading methods is to decide which value for androstenone and skatole or for the boar taint level is considered the threshold for classifying carcasses as positive or negative with respect to boar taint. This threshold should be determined by the risk each company wants to assume for boar taint, considering consumer sensitivity and acceptability and the prevalence of boar taint in the swine population (Aluwé et al., 2018, Christensen et al., 2019).
