Nguyen V. Non 1* and Nguyen T. Toan 2
4. Discussion and conclusion
The present study assessed the correlation between PCV2-IgG antibodies in vaccinated sows and their offspring. Thus, this purpose could allow defining the appropriate vaccination time for piglets. Under the conditions of this study, vaccination for pregnant sows has significantly improved their IgG concentration 20 days post-vaccination. After birth, piglet serum IgG concentration on the first day of age had a higher level and strong correlation with the pregnant sow at 110 days of gestation. Furthermore, all serum samples of these stages were PCV2 negative by Real-time PCR so that the antibody titers detected were most likely of maternal origin. Although not directly evaluating the neutralizing antibodies, the IgG content measurement ELISA method combined with the qPCR could indirectly assess the level of protection against PCV2 (Fort et al., 2009; Pileri et al., 2014; Oliver-Ferrando et al., 2016) The present study analyzed variables related to sow and litter characteristics to ascertain whether they affect MDA. These results show that the piglet IgG antibody was not significantly affected by sow parity and piglet birth weight. These results agreed with a recent result, the IgG concentration in colostrum was not significantly influenced by the sow parity (Segura et al., 2020), and piglet birth weight (Cabrera et al., 2012). Although serum IgG reaches its peak at day 110 of pregnancy, the concentration of IgG antibodies in colostrum is several times higher than in serum (Le Dividich et al., 2005; Segura et al., 2020). On the other hand, some research revealed several factors that influenced colostrum intake including birth order, litter size (Declerck et al., 2017; Le Dividich et al., 2017) and heterogeneous birth weight within litter (Charneca et al., 2021).
This work also aimed to evaluate the effect of piglet age on the decline of MDA. The level of IgG has decreased rapidly after birth and reached the half-life around 21 days, this result aligned with Opriessnig et al. (2004). Overall, the vaccine and sow parity did not affect the piglet IgG concentration for almost the duration of the study. Moreover, mixed-effect analysis has shown a significant effect of piglet age and sow antibody on the piglet IgG concentration.
Piglet age is the most crucial factor effect on piglet vaccination time due to the decline of MDA.
High MDA could be a potential interference with the development of an active humoral immune response (Fort et al., 2009; Fraile et al., 2012a; Martelli et al., 2016) but low MDA also have a potential infection of PCV2 (Fort et al., 2009). So, from this point of view, the appropriate vaccination time would be when MDA levels are high enough to protect the piglets (Fort et al., 2009) but low enough to minimize interference with vaccine antigens (Martelli et al., 2016).
On the other hand, Pileri et al (2014) when compared the antibody titers against PCV2 in porcine sera by immuno-peroxidase monolayer assay (IPMA) with the results of three commercial ELISAs found an excellent correlation, and the highest correlation was Ingezim Circo IgG (r2 = 0.93). Therefore, it seems that the optimal MDA S/P level to design vaccination for piglets should be higher than 0.8 but lower than 1.2 (Figure 1).
Figure 1. The correlation between PCV2-IgG levels in piglets and sows. High MDA (S/P >
1.2) could interfere with the vaccine and susceptible to PCV2 infection when S/P < 0.8. For calculation of piglet antibody from the equation, "Mean ± SD” of sow S/P was “1.59 ± 0.55”.
The application of the regression equation in this study could help determine the appropriate vaccination time for piglets. Depending on the level of sow antibody and in the case of the mean (mean S/P = 1.59), piglet vaccination can be from 23 to 28 days. However, with higher sow antibody (“Mean + SD” = 2.14), the piglet vaccination time should be from 28 to 37 days. In contrast, for the sows with lower antibody (“Mean – SD = 1.04), piglets born should be vaccinated earlier from 19 to 23 days of age. Hence, in the practical application, collecting blood samples from pregnant sows of 110 days and 21-day-old piglets were to evaluate the IgG serum concentration, then applying the regression equation of this study to design the piglet vaccination program.
In conclusion, vaccinating pregnant sows significantly improves the antibody level of sows before farrowing and induces high MDA levels in piglets. Based on the existing correlation and regression between the antibody in sows and piglets, this study could help to determine the appropriate time to vaccinate piglets. However, as multiple factors may influence the MDA levels, the present study represents a further investigation of the colostrum management and PCV2 sow vaccination scenario.
Acknowledgements
The authors would like to thank the swine team of Ceva Vietnam, and the farm animal caretakers and veterinarians for their willingness to collaborate in the study.
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TRIAL TO EVALUATE THE EFFICACY OF BIOLOGICAL CASTRATION VACCINE (IMPROVAC®) ON ESTROGEN HORMONE AND GENITAL ORGANS
IN FEMALE PIGS
Lai C. Danh1, Vo T. Hue2, Nguyen K. Quoc1, Nguyen T. A. Linh1, Du D. Phong2, Phan T.
Truc2, Doan T. V. Khanh1 and Do T. Duy1*
1Faculty of Animal Science and Veterinary Medicine, Nong Lam University, Ho Chi Minh City, Vietnam
2Zoetis Vietnam company, Ho Chi Minh City, Vietnam
*Email: [email protected] Abstract
Gonadotropin releasing hormone (GnRH) is secreted in hypothalamus and promotes the secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH) in pituitary gland, which play important roles in physiological maturity of female pig. Castration vaccine (IMPROVAC®) can stimulate the immune system of pigs to produce endogenous GnRH neutralizing antibodies, thereby reducing the maturation expression of sows. The aim of this study was to evaluate the effects of the biological castration vaccine on hormone secretion and reproductive organs of female pigs. A total of 20 healthy pigs, uniform in breed (LDxYSxDR), 12 + 0.5 weeks old, were assigned to 2 experimental groups. Group IF included 10 female pigs vaccinated at 12 and 16-week-old and Group EF included 10 entire female pigs non- vaccinated.
The sera were collected at 12, 16 and 23 weeks of age. The trial pigs were slaughtered and sampled genitals at 23 weeks of age. The anti-GnRH antibody titers of the pigs in IF group were highly positive at week age 16 (0.46 ± 0.04 ng/ml) and 23 (0.68 + 0.06 ng/mL) and were significantly higher (P < 0.05) than those in EF group at week age 23. Meanwhile, the pigs of IF group showed lower concentration of estrogen than EF group at 16 and 23 weeks old, respectively 44.16 vs. 59.43 and 39.30 vs. 91.34 pg/mL. At the time of slaughter, the reproductive organs of pigs in IF group were significantly smaller and lighter than those in EF group. The presence of secondary follicles of IF group were higher than that of EF group, in contrast with graafian follicles and lack of appearance of corpus luteum (CL) in EF pigs. The results showed that biological castration vaccine can stimulate pigs to effectively secrete anti- GnRH antibodies to reduce estrogen levels, which inhibits the development of genital organs in female pigs.
Keywords: castration vaccine, estrogen genital organs, female pigs, immunocastration 1. Introduction
The maturation and development of reproductive organs in female pigs is greatly influenced by the hypothalamic – hypophyseal – gonadal axis, of which gonadotropin releasing hormone (GnRH) is released from hypothalamus gland and controls the production of FSH (follicle stimulating hormone) and LH (luteinizing hormone) from the pituitary gland (Diekman et al., 1983). In female pigs, FSH stimulates the ovary to produce estradiol during follicular phase and progesterone during luteal phase (Marques et al., 2022). At midcycle, FSH level increases with LH to trigger ovulation (Taylor et al., 1995). Estrogen negative feedback occurs during follicles phase when it is still low, it increases to a high level at the near end of follicles phase and estrogen becomes a positive inducer of anterior pituitary (Messinis, 2006).
Follicles produce considerable amounts of steroid hormones, most notably estrogen which is secreted by granulosa cells within follicles (Strauss III & Williams, 2019). Estrogen again triggers the anterior pituitary gland to release more FSH and LH lead to ovulation (Marques et al., 2022). Therefore, inhibition of GnRH concentration indirectly decreases estrogen level and
growth of reproductive organs in female pigs. LH is also important for the development of medium sized follicles and ovulation (Raju et al., 2013). After ovulation, the luteinized cells of the follicle form the corpus luteum (Bates & Bowling, 2013). The presence of corpus luteum in the ovary is evidence of complete reproductive growth of female pigs.
Castration vaccine, IMPROVAC®, is usually indicated for reducing boar taint but it also affects the biological structures and physiology of female pigs (Schwarzenberger et al., 2022).
IMPROVAC® vaccine contains a modified form of Gonadotropin releasing hormone (GnRH), which is related to reducing LH and FSH releasing (Fuchs et al., 2009). The effectiveness of this vaccine was proved first time through the administration of GnRF-tandem dimer peptide at 10, 13, 21 weeks of age and the result showed that LH concentration in their serum significantly decreased lead to suppress reproductive function (Han et al., 2016). Several studies of IMPROVAC® vaccine as an immunocastration regime in male pigs but there is very little research in female pigs. Therefore, the aim of this study was to evaluate the effectiveness of IMPROVAC® vaccine at gonads level in gilt serum and their reproductive organ growth.
2. Materials and Method