TESTIS SIZE AFTER IMMUNOCASTRATION AS PARAMETER FOR THE ABSENCE OF BOAR TAINT

Immunization against GnRH-like peptides to immunocastrate boars can be very effective in preventing boar taint and in reducing testis weight (TW) and size (TS). Experiments using vaccines with different efficac ies resulted in a total of 203 male pigs with widely diverging TW and TS. The relations of the latter parameters with androstenone (AN) show ed that AN levels were always lower than 0.5 mu g/g (the limit for the sensory detectability of boar taint) when TW was < 150 g or TS was <9 cm. In Dutch practical circumstances, using commercial crossbreeds of pigs and a slaughterweight of +/- 115 kg, AN level in backfat will be the best indicator for the presence of boar taint. A relation between low TS or low TW and low serum testosterone also existed but less str ong. Skatole levels in backfat of 59 pigs were mostly low and not corr elated to TS or TW. In this series of experiments growth performance a nd carcass quality have not been evaluated. These economically importa nt performance parameters might have been less favorable in immunocast rates than in intact boars. However, supposedly these parameters were better than in neonatally castrated pigs, as early immunocastrates can benefit from the presence of male steroid hormones certainly until th e second vaccination at 18 weeks of age. The present results show that evaluation of anti-GnRH vaccination is convenient, compared to labori ous assays, and practical, as testis size can be examined visually bef ore slaughter. Early immunocastration appears to be a good alternative to prevent the occurrence of boar taint and to abolish the distastefu l practice of surgical castration of male piglets.