Entire Male Pigs

Table of Contents

1. Introduction
   1. Objectives
   2. Learning goals
   3. Teacher page
2. Entire Male Pigs
3. Castration of male pigs
   1. Statistics
4. Legislation and enforcement
5. Origin of boar taint
   1. Androstenone
   2. Skatole
6. Reasons for castration
   1. Increase the proportion of fat
   2. Increase consumer acceptance
   3. Reduce aggression
   4. Prevent unplanned breeding
7. Surgical castration
   1. Traditional surgical castration
   2. Anaesthesia combined with castration
   3. Gas analgesics
8. Problems related to surgical castration
   1. Animal welfare
   2. Pain and behaviour - the acute response
   3. Reduced growth rate and changed behaviour after surgery
   4. Health consequences
   5. Effect of age
   6. Consumer awareness
   7. Labour cost
9. Alternatives to castration
   1. Slaughter at lower weight
   2. On-line sorting
   3. Management
   4. Breeding and sperm sexing
   5. Perceptual masking of boar taint
   6. Immunocastration
   7. Immunocastration - physiology
   8. Immunocastration - practical implications
10. Completion
    1. Comments
    2. Self-assessment
    3. Key messages
    4. Further reading
    5. Evaluation
11. Acknowledgement

Androstenone

Androstenone is a testicular steroid with no hormonal activity produced in mature male pigs in parallel with anabolic hormones (see figure 4). Some androstenone accumulates in the back-fat (adipose tissue) and produces boar taint when heated. The levels of androstenone are regulated by the stage of puberty and the individual ability of the animal to synthesize and metabolize androstenone. In the regulation of androstenone levels, dietary factors are believed to be less important than for the skatole levels.

Figure 4: Schematic illustration on the production of androstenone. Source: Maria Algers.

After being produced by the Leydig cells, androstenone is either transported to the liver, where it is metabolized and excreted, or it is transported to the salivary gland where it is released in the saliva. There it is bound to a specific binding protein and serves as a pheromone to attract the sows in oestrus and induce a mating response. The third pathway is when androstenone is transported by the blood to the fat tissue, resulting in boar taint.

Production of androstenone is controlled by the neuroendocrine system, especially by the luteinizing hormone (LH), which is controlled by the gonadotropin-releasing hormone (GnRH), see Figure 5.

The control of sexual functions in both the male and female pigs starts with secretion of gonadotropin-releasing hormone (GnRH) by the hypothalamus. This hormone stimulates the anterior pituitary gland to secrete the two hormones luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH is the primary stimulus for the secretion of testosterone by the testes, whereas FSH helps to stimulate spermatogenesis.

Figure 5: Schematic illustration on the production of androstenone. Source: Improvac

Recent research shows that a human receptor is involved in consumer´s sensitivity to androstenone and further research in this field will aid consumer studies in the future (Lundström et al., 2009).