An optimal sensory detection protocol for boar taint and demonstrable reduction of boar taint by modified feed and immunocastration: these are the results of the doctoral thesis of Evert Heyrman, researcher at ILVO, UGent and KU Leuven. This research showed that the risk of boar taint – which can occur when male piglets are not castrated - cannot be completely eliminated regardless of the reduction strategy applied. Applying a suitable method to detect boar taint in the slaughterhouse remains the most critical factor for a successful transition to pig farming without (non-anesthetized) surgical castration.
On September 28th Evert Heyrman defended his doctoral thesis: 'Farm specific strategies for the reduction of boar taint'. Supervisors of the PhD are Prof. Dr. Nadine Buys and Dr. Steven Janssens of KU Leuven and Dr. Marijke Aluwé of Flanders Research Institute for Agriculture, Fisheries and Food (ILVO).
Increasing consumer concern for animal welfare has led to a commitment by the European pig sector to stop surgical castration of male piglets from 2018 onwards. An important precondition for this shift was the resolution of a number of practical and economic bottlenecks for the alternatives to surgical castration. The deadline has not been fully met, although in Flanders, as well as in Denmark, Germany, the Netherlands, Spain and the United Kingdom, intact boars are being kept to a greater or lesser extent. Flanders, one of the only European regions do to so, has also made a partial transition to rearing immunocastrates. However, a number of questions need further examination, including the risk of boar taint. This unpleasant smell and/or taste in pork fat and/or meat can be observed in about 4% of the carcasses. During his PhD research, researcher Evert Heyrman focused on the detection and reduction of boar taint and the effectiveness of measures to reduce boar taint as well as the application of immunocastration under practical conditions.
Five prerequisites for successful castration-free pig farming
In order to successfully evolve towards a pig sector free of non-anesthetized surgical castration in Europe and Flanders, i.e. rearing intact boars and immunocastrates, the following preconditions need to be met.
The first condition is the universal acceptance of one method to detect boar taint. Second, a European reference detection method is needed for each of the chemical components (androstenone, skatol and indol) that contribute to boar taint (recently met). The third prerequisite is a quick detection method for boar taint that is easily applicable in the slaughterhouse. Fourth, practical strategies to reduce the prevalence of boar taint are needed. The last prerequisite is that effective management measures must be found to reduce sexual and aggressive behavior in intact boars.
Boar taint detection and reduction, essential for rearing intact boars
The aim of Heyrman’s doctoral study was to contribute knowledge regarding the abovementioned five preconditions. The focus was on three research questions: 1) the optimization of a sensory detection method for boar taint that is applicable in a research context as well as in slaughterhouses; 2) the determination of boar taint prevalence and the identification of risk factors for boar taint in intact boars in Flanders; and 3) testing of strategies to reduce the prevalence of boar taint and (to a lesser extent) the prevention of sexual and aggressive behavior in intact boars.
Training protocol for boar taint evaluators
The soldering iron method is a sensory method to detect boar taint. This method is sometimes applied at the slaughter line (online) or afterwards at another location (offline). In this method trained persons heat a piece of pork neck fat with a soldering iron, then smell it and assign it a score. The scoring scale ranges from 0 (no abnormal smell) to 4 (very abnormal smell). To achieve consistent and reliable results, proper selection and training of the evaluators is essential. Within this study, the score of 3 evaluators was averaged to achieve a more reliable result.
The training of boar taint evaluators appears to contribute to consistent detection between and within evaluators even though the detection limits for boar taint components within the same evaluator may vary over time. Furthermore, it was found that 1) keeping the number of evaluators constant is essential to compare results, 2) not all components (androstenone, skatol and indol) contribute equally to sensory boar taint, and 3) it is important to smell a boar taint negative sample after smelling a positive sample before moving on to the next one, 4) smelling a boar taint strip with boar taint components does not help sensory detection.
Multiple risk factors for boar taint identified
The prevalence of boar taint on Flemish pig farms with intact boars was rather low: 5.6% in a first and 1.8% in a second observational study. However, comparing the prevalence from both studies was hampered by a different experimental design (e.g. different farms, varying number of batches per farm). In addition to the variation in boar taint prevalence between farms, there was also a 10% variation in prevalence between different batches within the same farm.
In the first observational study, the factors associated with a higher boar taint risk were: more skin damage/scratches on the carcasses (scored after slaughter), a lower lean meat percentage, and a higher outside temperature on the day of slaughter.
In the second observational study, the risk was linked to the occurrence of more aggression and stress, skin damage both in the barn and on the carcasses, slaughter in winter (lower risk in the summer), a lower crude protein content of the feed, and a lower lean meat percentage.
The results regarding temperature seem contradictory but are due to opposite mechanisms, namely the adolescent development of the pigs throughout the seasons (influence on androstenone) and the effects of temperature on liver metabolism (influence on skatol).
Feed modifications and immunocastration are most promising to reduce boar taint.
Finally, a number of reduction strategies were evaluated in two experimental studies. Adjusting the feed strategy (applying two commercially available feed additives) and applying immunocastration were most effective in reducing boar taint, although a certain risk of boar taint still remained. In immunocastrates, this may be explained by either so-called 'non-responders' or poorly executed vaccinations. Varying the residence time of intact boars in the slaughterhouse waiting area and housing boars and gilts in another compartment were not effective in reducing boar taint.
The findings of this PhD contribute to fulfilling the required preconditions for a European pig sector free of surgical castration. First, the findings regarding the optimal sensory detection method help to harmonize detection methods in the research. Second, the experience of training in slaughterhouses shows that, at least in the short term, sensory detection of boar taint is a viable option until more efficient and objective methods become available. Third, feed modifications (effect on skatol) and immunocastration (effect on skatol and androstenone) are currently the most promising reduction strategies for boar taint. Immunocastration is also effective in reducing sexual and aggressive behavior in boars. For both, however, there is always a certain risk of boar taint, thus boar taint detection will therefore always be required as a safety net.
"Applying a suitable, affordable detection method in the slaughterhouse remains the most critical precondition", says researcher Evert Heyrman.
It is impossible to completely eliminate the risk of boar taint that occurs in the absence of surgical castration, regardless of the reduction strategy used. As a result, the application of a suitable detection method in the slaughterhouse remains the most critical factor for a successful transition to a pig farm without surgical castration in Europe, at least for the foreseeable future. Chances are that multiple alternatives for surgical castration will be implemented side by side in the European pig sector to meet market demands.
Greet Riebbels, ILVO communication: firstname.lastname@example.org, 0486 26 00 14
Evert Heyrman, PhD, email@example.com, 09 272 25 67
Marijke Aluwé. ILVO promotor, Marijke.Aluwe@ilvo.vlaanderen.be, 09 272 25 87
Also read this article about COST IPEMA, a European network on alternatives to piglet castration that included ILVO, other knowledge centers and stakeholders from across Europe.
The TAINTLESS project was subsidized by the Agency for Innovation and Entrepreneurship (VLAIO, IWT/120767) and the sector.