Bedrijfsspecifieke strategieën voor de reductie van berengeur

Because of growing animal welfare concerns, the European pig sector has committed itself to abandon surgical castration of male piglets, providing its practical and economic feasibility. Two promising alternatives to surgical castration are rearing entire male pigs (no castration in any form) and rearing immunocastrates (no surgical castration of piglets but inhibition of the male reproductive system by two vaccinations). Certainly, when rearing entire male pigs there is a risk of ending up with boar taint in some carcasses, an unpleasant odor and/or taste of pork fat and/or meat. Flanders has already partly made the transition towards rearing entire male pigs and, as the only region in Europe, towards immunocastrates. Denmark, Germany, the Netherlands, Spain, and the United Kingdom have all adopted rearing entire male pigs to varying extent. Five prerequisites need to be met for a successful transition to a surgical castration-free European (and Flemish) pig sector. The first condition is a universally accepted detection method for boar taint. Second are European reference detection methods for each chemical compound contributing to boar taint (recently attained). Third is a rapid detection method for boar taint applicable at slaughter plants. Fourth is the development of strategies to reduce the prevalence of boar taint. Fifth is applicable strategies to reduce sexual and aggressive behavior of male pigs reared without surgical castration. When the choice is made for surgical castration with analgesia and/or anesthesia or sexing of semen to produce only female pigs becomes possible, boar taint would no longer be a problem. Hence these prerequisites are then not applicable. In this PhD, we contributed to all five conditions with a focus on 3 research questions. First, optimizing an olfactory detection method for boar taint applicable both in research and practice (slaughterhouses). Second, establishing prevalence of and identifying risk factors for boar taint in entire male pigs in Flanders. Third, testing strategies to reduce the prevalence of boar taint as well as (to a lesser extent) sexual and aggressive behavior. We met our three research goals concerning detection of, prevalence of, risk factors for and strategies to reduce boar taint as well as to reduce sexual and aggressive behavior. Concerning the training protocol for training boar taint assessors we found that training mainly contributes to consistent detection between and within assessors even though detection limits of boar taint raters can vary within assessors over time. Concerning the optimal olfactory detection method in research we settled for the hot iron method (assessors heat a sample of pork fat using a soldering iron, smell it, and give it a score) using a scoring scale from 0 (no aberrant odor) to 4 ( very strong aberrant odor) and using the average score of 3 assessors as the final score. Furthermore we found that 1) keeping the number of assessors consistent is essential to ensure the comparability of results, 2) not all compounds contribute equally to olfactory boar taint, 3) it is good practice to smell a sample negative for boar taint after identifying a sample positive for boar taint before continuing, 4) smelling a boar taint compound solution on smell strips prior to olfactory detection of samples for boar taint does not improve performance. Concerning the prevalence of boar taint on Flemish farms rearing entire male pigs revealed a generally low prevalence of 5.6% in the first and 1.8% in the second observational study (comparability of prevalence between both studies is limited however). In the first observational study, higher skin lesion scores measured after slaughter, lower lean meat percentage, and higher outside mean temperature on the day of slaughter were linked with higher boar taint risk. In the second observational study relevant risk factors were, aggression and stress, winter season over summer, lower crude protein content of the feed, and lower lean meat percentage. Finally, a set of reduction strategies were evaluated in two experimental studies. Feed adaptations and immunocastration were effective in reducing boar taint but some boar taint risk remained. Varying the time spent in lairage and rearing entire male pigs separate from gilts were not effective in reducing boar taint. These findings bring the required conditions for a European surgical castration-free pig sector somewhat closer. First the findings concerning the optimal olfactory detection method contribute to the effort of harmonizing detection methods used in research. Second, while not part of one of the research goals, comparing the olfactory detection method to chemical boar taint contributes to the discussion of determining cutoff concentrations used in a reference method. Third, the experience with training in slaughterhouses shows that at least in the short-term, olfactory detection of boar taint is a viable option until a more performant and objective method becomes available. Fourth, feed adaptations and immunocastration are currently the most promising strategies to reduce boar taint prevalence. Some risk of boar taint remains however, and boar taint detection will likely remain essential as a safety net. Likely, no one singular strategy will be implemented across the European pig sector. Last, immunocastration is effective in reducing aggressive behavior compared to rearing entire male pigs. The risk of boar taint that arises when surgical castration of male piglets is abandoned is reduced but not eliminated by any of the available reduction strategies. Hence applying a suitable detection method in the slaughterhouses is for the foreseeable future the most critical factor to achieve a successful transition in Europe to a surgical castration-free pig sector.

Jaar van publicatie:2020

Toegankelijkheid:Closed