The aim of this study was to investigate the effect of a vaccine against gonadotropin-releasing hormone
(GnRH), Improvac® (Pfizer Ltd), administered at a pre- or early pubertal stage on boar taint, hormonal
status and reproductive organs. Crossbred male pigs (Swedish Yorkshire dams
×Swedish Landrace sires
or Swedish Yorkshire sires, n = 192) were at birth randomly allocated to four groups: one group of pigs
surgically castrated without anaesthesia before age 1 week, a second group of early vaccinated pigs
given Improvac at ages 10 and 14 weeks, a third group of standard vaccinated pigs given Improvac at
ages 16 and 20 weeks, and a fourth group of entire male pigs. Following the second vaccine injection,
antibody titres increased rapidly, accompanied by a rapid decrease in testosterone and a slower decrease
of skatole in plasma to the same low levels as for surgically castrated pigs. At slaughter, the levels of
androstenone and skatole in adipose tissue were low in surgically castrated and vaccinated pigs, whereas
entire male pigs had elevated levels (p < 0.001). Similarly, oestradiol was at low levels for surgically
castrated and vaccinated pigs, whereas entire male pigs had elevated levels (p < 0.001). IGF-1 was lowest
for surgically castrated pigs and highest for entire male pigs, with vaccinated pigs at an intermediate level
(p < 0.001). At slaughter, reproductive organs were small in pigs vaccinated with Improvac, and smaller
in pigs vaccinated early (p < 0.001). Under our experimental conditions, early vaccination with Improvac
can be used as an alternative to the recommended schedule with maintained control of boar taint and
testicular secretory activity.