Assessment of the efficacy of a gonadotropin releasing factor (GnRF) analog to suppress ovarian function in gilts under pre-clinical and clinical conditions.

Background: The administration of a gonadotropin releasing factor (GnRF) analog to pigs has proven to induce antibodies against endogenous GnRF. In gilts (young female pigs), the subsequent blocking of GnRF activity by specific antibodies results in a temporary suppression of ovarian activity and sexual maturation. One pre-clinical and two clinical studies were conducted to assess the ability of the GnRF analog to produce immunologically suppression of the ovarian function, preventing gilts from reaching puberty before harvest, at 27 weeks of age.

Results: In the three studies, a significant reduction of size and weight of reproductive organs and gilts in oestrus was demonstrated in vaccinated gilts compared with intact gilts. A significant increase in anti-GnRF antibody levels in sera was observed after the 2nd dose, which lasted until the end of the study in each of the protocols used. Progesterone levels were significantly reduced from 6 to 8 weeks after 2nd vaccination in clinical studies 2 and 1 respectively, and from 6 weeks after 2nd vaccination in the pre-clinical study. Estradiol levels were below the limit of detection for clinical study 2 and significantly reduced in vaccinated gilts at the end of the pre-clinical study and the clinical study 1.

Conclusions: Vaccination of gilts with a GnRF analog with two different protocols (1st dose from 10 to 14 weeks of age, and a 2nd dose 8 or 4 weeks later) was effective in reducing the development of puberty for at least 9 weeks post 2nd dose. These results confirm the flexibility of vaccination programs for veterinarians and producers which can be adapted to pig management practices in commercial farms.