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Anti-GnRH vaccine prevents unwanted pregnancies in Iberian gilts

A vaccine that temporarily delays puberty in gilts may help Iberian pork producers avoid unwanted pregnancies in free-range herds.

Iberian pigs, bred primarily in southwestern Spain and Portugal, are used in the production of premium regional pork products. Many are raised at least partly outdoors, or “extensively,” but the open terrain leaves gilts vulnerable to impregnation by wild boars — and producers vulnerable to the production and welfare risks associated with unwanted pregnancies.

To avoid these issues, Iberian gilts have traditionally been castrated by ovariectomy around 2 to 3 months of age. However, a new study presented at the 2017 European Symposium of Porcine Health Management shows that an estrus-suppressing vaccine may provide an effective and less invasive alternative to this practice.1

The subcutaneous vaccine stimulates the gilt’s immune system to produce antibodies to gonadotropin-releasing hormone (GnRH), a naturally occurring hormone that triggers the onset of puberty. By neutralizing GnRH, the vaccine temporarily blocks ovarian activity, thereby suppressing estrus and making it virtually impossible for vaccinated gilts to become pregnant.

“In addition to having a negative impact on production performance and meat quality, unwanted gestations represent an animal-welfare problem and a potential concern for consumers who are increasingly inquisitive about animal farming,” said Alvaro Aldaz, DVM, director of new product development for swine at Zoetis, and one of the study’s authors.

“This research confirms that anti-GnRH vaccination effectively suppresses estrus, making it a good alternative for producers raising gilts under extensive conditions.”

Study results

In a recent trial of the vaccine in Spain, investigators enrolled 30 gilts maintained in extensive conditions. At 18, 22, 34 and 46 weeks of age, half the gilts were given the vaccine according to manufacturer’s instructions, and the other half served as control.

Efficacy was evaluated by measuring anti-GnRF antibody titers, progesterone and estradiol levels at regular intervals throughout the study and by comparing the size of reproductive organs between groups at the end of the study, after slaughter at the age of 60 weeks.

Results indicate that while control pigs reached sexual maturity, vaccinated pigs failed to go into estrus due to successful GnRH inhibition. As expected, this led to vaccinated females having smaller reproductive organs at the time of slaughter due to atrophy. At the end of the study, uterine weight and length were significantly greater in control females than in vaccinated pigs, 712 g versus 69 g, respectively (p < 0.0001), and 2,889 mm versus 615 mm, respectively (p < 0.0001).

Similar results were found in ovarian weight and activity. Two control sows were pregnant at slaughter due to the uncontrolled mating with a wild boar.

Effective tool

Based on these findings, investigators concluded that the vaccine is an effective tool for suppressing estrus and thus preventing pregnancy in Iberian gilts raised under extensive conditions.

The vaccine is currently approved for use in gilts in Spain and Portugal. In male pigs, a similar vaccine for the reduction of boar taint is used as an alternative to physical castration in more than 60 countries throughout the world.





1. “Use of an anti-GnRF vaccine to suppress estrus in Iberian gilts reared in commercial extensive conditions in Spain.” ESPHM 2017 abstract book:






Posted on August 21, 2017

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