Surgical castration without anesthesia is the most common practice
to control boar taint aswell as aggressive and
sexual behavior, both inmales and females, throughout the rearing period
and in the pre-slaughter period. In Europe, female castration is only
allowed in Spain for pigs farm
outdoors, with prolonged analgesia
and anesthesia . This fact depends on
the peculiarities of the production system of Iberian pigs: a sacrifice to
heavy weights (N150 kg) and raised under free-range conditions,
which can cause unwanted pregnancies . Moreover, in Europe,
there is a plan to voluntarily end surgical castration of pigs by 2018
.
Recently, a vaccine against the gonadotrophin releasing factor
(Improvac®, Pfizer Animal Health) has been approved for use in more
than 60 countries including Australia, New Zealand, Brazil, Mexico,
Switzerland and the EU, and offers a more welfare-friendly alternative
to surgical castration . Additionally,research has shown that immune-castrated pigs show less aggressive
and sexual behavior , and are found to have fewer skin lesions compared to entire males , therefore offering a welfare advantage.
Improvac® has no intrinsic hormonal or chemical activity. Successful immunization with Improvac® requires two
doses of the vaccine to be given at least 4 weeks apart, and the second
dose must be administered 4–6 weeks before slaughter . Until now, studies on immune-spaying of pigs have focused
on the response in a short period after vaccination, from the second injection
to slaughter (4–6 weeks). However, it is not always practical to
vaccinate heavy pigs, especially if they are group-penned . Therefore, longer time between the second injection and slaughter
is desirable. To make this time increase possible, the long-term
effects of vaccination with Improvac® should be studied in females, as
they have been studied in males