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 efficacies resulted in a total of 203 male pigs with widely diverging TW and TS. The relations of the latter parameters with androstenone (AN) showed 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 strong. Skatole levels in backfat of 59 pigs were mostly low and not correlated to TS or TW. In this series of experiments growth performance and carcass quality have not been evaluated. These economically important performance parameters might have been less favorable in immunocastrates 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 the second vaccination at 18 weeks of age. The present results show that evaluation of anti-GnRH vaccination is convenient, compared to laborious assays, and practical, as testis size can be examined visually before slaughter. Early immunocastration appears to be a good alternative to prevent the occurrence of boar taint and to abolish the distasteful practice of surgical castration of male piglets.