Effect of active immunization against GnRH on androstenone concentration, growth performance and carcass quality in intact male pigs

The objective of this study was to investigate the efficacy of active immunization against gonadotropin releasing hormone (GnRH) in male pigs and to compare it with surgical castration. Piglets were randomly assigned to two groups, one of 263 animals for surgical castration (SC) and one of 270 animals for immunocastration (IC). Surgery was done at 14 days of age and vaccination (Improvac®, CSL, Australia) performed twice at an interval of 4-5 weeks with the second injection given 4-7 weeks before slaughter. At slaughter, testes were weighed and fat samples collected for androstenone analysis. Androstenone was tested olfactorially by heating salivary glands in a microwave oven. Daily growth rate and meat quality were assessed in all animals. Regarding mean androstenone concentrations in backfat, no significant difference was found between SC and IC (0.042 (0.041; 0.044) μg/g vs. 0.058 (0.044; 0.071) μg/g; mean (95% confidence interval)). Testes weight was significantly (P<0.001) smaller in immunized (230.8 g (218.23; 243.52)) as compared to normal boars (761.8 g (722.77; 801.01)) of the same age, as a reference. In this study, androstenone production was suppressed in all vaccinated animals and the carcasses given free for consumption. Mean daily growth gain was not significantly different between SC (0.817 kg (0.804; 0.830)) and IC (0.827 kg (0.814; 0.840)), although there was a trend for better performance in the latter group. The yield of lean meat was significantly (P<0.001) improved in IC (54.50% (54.26; 54.73)) when compared to SC (53.76% (53.53; 54.00)). From our results, we conclude that vaccination against GnRH is a practical and effective method to suppress androstenone synthesis. Pain and stress associated with surgical castration can thus be avoided.