1. Introduction
For German pork production, about 80% of all male piglets are surgically castrated within their first week of life [
1,
2]. Consumers evaluate surgical castration without pain-relieving methods very critically [
3]. In September 2009, this led German stakeholders of the pork chain to commit to the goal of ending surgical castration of piglets in the so-called ‘Düsseldorfer Erklärung’ [
4]. These developments have also resulted in an amendment of the German animal protection law in 2013. From January 2019, piglet castration without anesthesia or analgesia was to be outlawed. Contrary to the planned change in the law, the government of the Federal Republic of Germany agreed in November 2018 to postpone the implementation of the amendment by 2 years [
5]. As its reason, the German government stated that there are no competitive alternatives available, and that a prohibition of surgical castration without pain-relief could have a negative impact on German pig production [
6].
Alternatives to surgical castration are pork production with boars or with immunocastrates [
7,
8]. Although these procedures are available in practice, their market shares are low. In Germany, about 20% of male pigs are fattened as boars, and less than 1% as immunocastrates [
1]. The acceptance of pork production with boars is limited because of the risk of unpleasant boar taint in the carcass, which can be ascribed to an excessive accumulation of the compounds androstenone and skatole [
9,
10]. A large part of the population is sensitive to skatole above a threshold of 0.25 µg/g liquid fat [
10,
11]. Because of a genetic polymorphism, only a lower proportion of the population is sensitive to androstenone above a threshold of 0.5–1.0 µg/g in liquid fat [
10,
12]. What both compounds have in common is that most consumers who are sensitive to these compounds dislike them [
13]. In order to sort out boar-tainted meat, carcasses of boars are currently evaluated at the slaughter line by the human nose test [
14]. However, under commercial conditions at the slaughter line, the reproducibility of valid results is only 23%, so it is highly likely that boar-tainted pork will be undetected and reaches consumers [
15]. Objective at-line methods of detecting androstenone- and skatole-tainted carcasses have been developed and have a high potential for being implemented for commercial use at the slaughter line under real-time conditions [
16]. However, commonly accepted thresholds for boar taint compounds to exclude tainted pork from the fresh meat market do not exist. Some research has been done to evaluate possibilities of using tainted pork with skatole levels up to 0.3 µg/g liquid fat and very high androstenone values above 3.5 µg/g liquid fat for processing, after blending it with meat from barrows or gilts [
17]. However, the processing characteristics of pork from boars are unfavorable because of a higher proportion of polyunsaturated fatty acids, which makes it unsuitable for processing traditional dry-cured products [
18].
Immunocastration is an active immunization against the hormone GnRH (Gonadotropin-releasing hormone) by vaccinating the boars twice with the vaccine Improvac® (Zoetis Inc., Parsippany, New Jersey, US). After the second vaccination, the secretion of LH (Luteinizing hormone) is reduced and testicular functions cease temporarily, so that from a physiological point of view the animals are barrows, with similar behavioral, metabolic, and meat quality characteristics. Immunocastration can therefore reliably prevent boar taint and can be regarded as a sustainable alternative to surgical castration and pork production with boars that meets animal welfare aspects as well as pork market requirements. Improvac® is licensed for commercial use in Europe with no technical or legal limitations and can be used for conventional as well as for organic pork production. Knowledge gaps on the potentials of this technique within the value chain prevent a more extensive market relevance [
19]. Producing boars or immunocastrates can also be very attractive and cost-effective from an economic point of view [
6], since the feed efficiency of boars and immunocastrates is higher than that of barrows [
20,
21]. In Germany, there are different carcass pricing systems for boars and barrows. It is currently unclear to which pricing system immunocastrates will be assigned, even though this is crucial for economic efficiency [
6]. In addition, it is still unclear what effects a quantification of androstenone and skatole values at the slaughter line will have on the profitability of pork production with boars or immunocastrates, and on the use of boar-tainted meat. Penalty systems linked to boar taint are already used in France and Norway, and are likely to be also implemented in other European countries as market shares of boars and immunocastrates increase [
14]. In order to enable a sustainable production of boars or immunocastrates in Germany, both alternatives must be critically analyzed under different economic scenarios by using risk scenarios for boar taint and evaluating immunocastration under different pricing systems.
4. Discussion
Surgical castration without pain relief is considered unacceptable by society. The fattening of boars and immunocastrates is regarded as animal friendly by some stakeholder groups and discussed as potential alternatives to the fattening of barrows. Both immunocastrates and boars have a better FCR than barrows [
32], which is more efficient from an economic point of view, as less feed is needed to produce the same amount of pork. On the other hand, these production systems generate additional production costs due to extra working time and additional vaccination costs [
28,
33]. In addition, no objective boar taint detection systems are currently in use at slaughterhouses and potential reductions in the value of carcasses by boar taint may reduce the profitability. Because of the small market share of immunocastrates on the German pork market, it is unclear at the moment how these carcasses will be priced. This study therefore analyzed the economic impact of immunocastration and boar fattening under different pig carcass pricing systems, including the occurrence of boar taint.
In the present study, feed composition was based on the feed requirements of boars, which means that there is further optimization potential for immunocastrates and barrows, as a less expensive feed with reduced protein and energy content might be appropriate. Such corrections within the calculation would potentially worsen the profitability of pork production with boars even more when compared to immunocastrates or barrows. All animals, irrespective of treatment and weight, were slaughtered in two groups, either at 27 or 28 weeks of age, and not according to the optimal slaughter weight. Similarly, the feeding phases followed the same timeline and were not adapted to weight gain, treatment group, and live weight. This may mask group-specific effects, as the feeding strategy similarly to feed composition should differ between the groups (B, IC, and BA) to optimize performance data, as well as to avoid excessive nitrogen excretion [
34,
35]. Barrows of the used genotype in particular have a higher ADG and would switch earlier to a different feeding period than boars or immunocastrates [
32]. In future research, optimal feeding strategies for respective groups should be considered.
The performance data of the experiment show that immunocastrates had higher ADG compared to barrows and boars. This is caused mainly by the performance of immunocastrates in the last feeding period after the second vaccination, which results in an increased feed intake and a higher growth rate [
21,
32]. Some studies confirm our results and show that immunocastrates grow faster over the entire fattening period than barrows and boars [
20,
21]. In another study [
32], however, barrows revealed a higher ADG than immunocastrates and boars. Such differences may be explained in part by the genotype used in the study. Crossbreds with Belgian Pietrain, for example, have a reduced growth rate before and after the second vaccination than, for example, Duroc crossbreds. In both genotypes, however, the growth rate increased in the two weeks following the second vaccination compared to the growth rate between the first and second vaccination [
36]. This may help to explain why, in typical German pig fattening farms, the ADG of barrows is higher than in immunocastrates. Moreover, the effect of slaughter weight has to be considered, as animals are slaughtered at a lower live weight compared to the experimental trials and thus the last feeding period is shorter than in our experiment. In this study, FCR is more efficient in immunocastrates as well as in boars, which is also illustrated by previous studies [
20,
21,
32].
In our study, the carcass data (weight of carcass parts) were adapted to the results obtained via the Auto-FOM III formula. In the case of immunocastrates and boars in particular, however, it can be assumed that this study underestimates the weight of carcass parts (especially the shoulder), since other studies show that carcass yields and the output of valuable meat in immunocastrates is higher than in boars or barrows. Compared to boars, immunocastrates also have higher belly weights [
20]. Actual Auto-FOM III data of immunocastrates, however, which would be crucial for future calculations, are not currently available. The dressing percentages of boars and immunocastrates compared to barrows were even worse in this study than in previous studies [
20,
21], indicating higher economic losses in pork production with boars and immunocastrates compared to the baseline.
All immunocastrates responded well to the vaccine in this study, and no non-responders with boar-tainted carcasses were detected. However, several reviews assume a proportion of non-responders of up to 3% [
18,
37,
38]. This would worsen the profitability of immunocastration, as it would result in a certain number of boar-tainted carcasses above the thresholds. Furthermore, the proportion of tainted boar carcasses is very high in this study and thus reduces the profitability of pork production with boars. An international study by Walstra and co-authors [
39], with different genotypes produced under different conditions in Europe, revealed very high androstenone (>1 μg/g liquid fat) concentrations in 29% of the boars, whereas a higher proportion of boars were affected by skatole levels above 0.25 μg/g liquid fat compared to our study. Nonetheless, more objective boar taint detection systems at the slaughter line are essential in valuing carcasses with regard to boar taint, and would worsen the profitability of boar fattening also for the 29% of boars affected by boar taint.
By the end of 2018, Tönnies Holding ApS & Co. KG introduced a new boar pricing system in Germany. This has even further reduced the economic profitability of boar fattening compared to the baseline [
6,
28]. The impact of the new boar pricing system on the profitability of immunocastration is also negative and makes the technique economically unviable [
28]. In a recent study by Verhaagh and Deblitz [
28], the production of pork with immunocastrates was more profitable in all typical German pig fattening farms compared to the baseline (barrows). Although producing immunocastrates generate higher production costs, they were compensated by better FCR, higher ADG, and a shorter fattening period. In the study by Verhaagh and co-authors [
28], however, the calculation was based on the ADG values of the entire fattening period, which resulted from higher ADG after the second vaccination. However, in this present study, it could be shown that the last feeding period had a positive effect on the ADG of the entire fattening period, but was economically not sufficient to compensate for the lower ADG of the earlier fattening periods. Furthermore, performance data of this trial declined in relation to the typical farms, as animals were fattened and slaughtered on fixed dates so that greater economic efficiency might be achieved through optimized management of feeding, fattening periods, and age at slaughter.