Factors affecting the level of androstenone
- Michel Bonneau1
© Bonneau.; licensee BioMed Central Ltd. 2006
Published: 7 August 2006
As pointed out in Øystein Andresen' s previous presentation, androstenone (5α-androst-16-ene-3-one) is one of the major compounds responsible for boar taint. It belongs to the family of the 16-androstene steroids that are synthesized in the testis together with androgens and estrogens. The present paper borrows a lot of its content from previous reviews .
Androstenone levels in entire male pig populations
Biosynthesis, accumulation in fat and elimination of androstenone
The biosynthetic pathways of the 16-androstene steroids have been described by David Gower at Guy's hospital in London . A simplified scheme is presented in Figure 3. The overall steroid synthesis is dependent on sexual maturity. The balance between 16-androstene steroids (with no hormonal action) and androgens and estrogens (responsible for the improved performance of the entire male compared to the castrate) depends on the activity of the enzyme complex andien-β synthase. To achieve high rates of androstenone synthesis a pig has to be sexually mature and exhibit high andien-β synthase activity.
The effect of age and weight on androstenone levels
The intensity of androstenone synthesis is low in the young piglet, and then increases steadily during the establishment of puberty [6, 7], concomitantly with the increase in production of the other testicular steroids, androgens and estrogens.
Management factors affecting androstenone levels
Management factors affecting sexual maturation have some, but little, effect on fat androstenone levels. Social factors do not have consistent effects. However, "birth to slaughter" systems, avoiding the mixing of unrelated animals, seem to result in lower androstenone levels . Photoperiod has a limited influence on androstenone levels, decreasing day length resulting in earlier sexual maturity and slightly higher androstenone levels . High energy feeding is associated with acceleration of pubertal development and increased androstenone levels [12, 13].
Genetic factors affecting androstenone levels
Fat androstenone levels are mostly dependent on genetic factors affecting sexual maturation, potential for androstenone synthesis and, possibly, androstenone clearance (Figure 3). This will be developed in Jim Squires' presentation later on today.
Drastic reductions in androstenone contents have to be achieved in order to get boar taint free meat. Management factors have a very limited impact on androstenone levels, in contrast with skatole. The required drastic reduction in androstenone levels can be achieved only with very efficient methods.
A first approach is to select animals with a low potential for androstenone accumulation in fat (see presentation by Jim Squires). The advantage is that androgen and oestrogen steroid production may be kept at a sufficient level to benefit from the better feed efficiency and higher leanness of the entire males. The drawbacks are that boar taint related to substances other than androstenone is not affected.
The second approach is to eliminate or reverse sexual development (EFSA, 2004 ). This can be achieved via i) down regulation of the hypothalamic-pituitary-gonadal axis by exogenous hormones (not an option in the EU), ii) castration with chemicals (not sufficiently investigated so far) or iii) Immunocastration (see presentation by Stig Einarsson). The advantage is that all boar taint substances are affected, the drawbacks are that all or part of the better performance associated with entire males is lost.
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