| Reproduction and lactation are important factors which reflect the performance of dairy cattle. The explanation of the development/resumption laws of cows'reproductive system plays a significant role in the full development of the potential for cows' reproduction and new reproductive technologies. Modern biotechnology has been used to improve the milk level of Dairy cows, which is the key to improving the economic efficiency of dairy farms. The first part of this study is to investigate the law of uterine involution and ovarian function resumption of Chinese Holstein dairy cows with different parities by B-mode ultrasound during postpartum, so as to provide the research basis for improving the fertility of postpartum dairy cows. The second part is to study the role of somatostatin gene immunization on reproductive function recovery and lactation performance of dairy cows by genetic immunization technology, and to provide the basis for the development of genetic vaccine which improve the fertility and lactation of dairy cows. A novel somatostatin DNA vaccine—pVGS/2SS-asd was tested on the rat model prior to the dairy cow, and used to explore the effects on the fertility and lactation performance of rats. The safety issue of this DNA vaccine on rats was also evaluated. These results provided the basis for the application of large animals (such as dairy cows). Then postpartum dairy cows were immunized against the pVGS/2SS-asd somatostatin DNA vaccine, exploring the effects on the fertility and lactation performance of the postpartum dairy cows.1. Study of uterine involution and resumption of ovarian activities in postpartum dairy cows with different parities.Favorable uterine involution and ovarian activity are very important for the next pregnancy and the shorter calving interval of postpartum cows. The objective of this study was to evaluate the effect of parity on uterine involution and resumption of ovarian activity in Chinese Holstein dairy cows after calving under similar postpartum nutritional and lactational conditions.46 Chinese Holstein dairy cows in various parities (primiparous=18; biparous=13; multiparous= 15) were selected. The status of uterus and ovaries was detected by ultrasonography. According to DHI (Dairy Herd Improvement) standard method, dry matter intake (DMI), milk yield, body condition score (BCS) were determined, and estradiol (E2) concentration in milk samples were measured by radioimmunoassay (RIA). The results showed that days of the previous gravid uterine horn involution were significantly greater in primiparous dairy cows than in biparous and multiparous dairy cows. Days from calving to ovulation (first and second) and the number of follicular waves to first ovulation were also significantly greater in primiparous cows than in multiparous cows. In summary, under similar postpartum nutritional and lactational conditions, postpartum uterine involution and resumption of ovarian activity became progressively shorter as the number of parity increased in Chinese Holstein cows2.The effects of immunization against a novel somatostatin DNA vaccine—pVGS/2SS-asd on fertility and lactation in female rats.In order to investigate the effects of immunization against a novel somatostatin DNA vaccine—pVGS/2SS-asd on fertility and lactation in female rats, and analyze the effects of immunization doses and delivery routes on immune effect of this DNA vaccine,216 female Sprague-Dawley rats were randomly divided into 9 groups,24 per group. Test groups:rats of T1-T3 groups were primarily intramuscular immunized against pVGS/2SS-asd in high (2×109 CFU/200μL), middle (2×108 CFU/200μL) or low (2×107 CFU/200μL) dose; rats of T4-T6 groups in the same dosage as T1-T3 groups were primarily subcutaneous immunized against pVGS/2SS-asd s. Control groups:rats of CO group (half intramuscular injection and half subcutaneous injection) were immunized against 10% aluminum hydroxide gel saline (200μL); rats of C1 group were intramuscular immunized against C500 (2×109 CFU/200μL); rats of C2 group were subcutaneous immunized against C500 (2×109 CFU/200μL). Booster immunizations in the same dosage as the primary immunization were performed twice at 4-week intervals. The results showed that this novel pVGS/2SS-asd somatostatin DNA vaccine had good immunogenicity, induced a high level of immune response, and maintained a longer time (approximately 11-13 ws) by booster immunization in female rats. In the delivery routes, intramuscular immunity in the antibody absolute value (OD= 0.823±0.075) and persistent immune response (approximately 13 ws) was more advantages than subcutaneous immunity. In dose effect, there was no dose-dependent among all tests, and middle dose groups of two delivery routes were obvious advantages than other dose groups. Whether intramuscular or subcutaneous, the reproductive performance of all rats immunized with different doses was not affected. However, pVGS/2SS-asd somatostatin DNA vaccine in postpartum lactating rats contributes to the growth of offspring, and improves the lactation performance of female rats indirectly. Weaning weight gain (215.8±18.8 g) of offspring of the middle dose intramuscular group was significantly higher than those of other groups, with a significant difference between the middle dose intramuscular group and the control group, and followed by the middle dose subcutaneous group (212.2±13.6 g). 3.Safety evaluation of somatostatin DNA vaccine in chromosomal integration.At the end of immunization against pVGS/2SS-asd somatostatin DNA vaccine in rats with intramuscular or subcutaneous injections, multiple tissues such as heart, liver, spleen, lung, kidney, ovary and muscle were removed from each female rat of test groups, respectively. Moreover, tissue samples of the pups, such as heart, liver, spleen, lung and kidney were also collected after weaning, respectively. The genomic DNA was extracted, and then the genomic DNA samples were detected by sensitive PCR method. The results showed that the plasmid was not integrated into maternal and offspring genomic DNA, and the result revealed that the somatostatin DNA vaccine in chromosomal integration was safe to rats.4. Effects of Somatostatin gene immunization on the reproduction and lactation performance of dairy cows.The purpose of this study was to explore the effects of the new somatostatin DNA vaccine—pVGS/2SS-asd on the reproduction and lactation performance of postpartum dairy cows.40 postpartum cows were randomly divided into 4 groups,10 per group. At 7d after calving,3 test group cows were primarily intramuscular immunized against pVGS/2SS-asd in high (1×1011 CFU/1mL), the middle (1×1010CFU/1mL), and low (1×109 CFU/1mL) dose; the control group cows were intramuscular immunized against 10% aluminum hydroxide gel saline(1mL). Booster immunizations in the same dosage as the primary immunization (injection day as 0 d) were performed twice at 4-week intervals. The results showed that the novel pVGS/2SS-asd somatostatin DNA vaccine for cows had good immunogenicity and could induce a certain intensity of immune response. High dose group in the induction of the maximum antibody peak value (OD= 0.490±0.171) and the persistent high proportion of antibody positive cattle (100.0% for 7 w) had obvious advantages than other dose groups. After immunization, there was no significant difference among all the groups in the gravid uterine horn and uterine cervical involution, intervals of first ovulation and ovulation follicle diameter, this somatostatin DNA vaccine did not adversely affect the reproductive performance of dairy cows. Moreover it also confirmed that in the similar nutritional conditions, this vaccine improved the lactation performance of cows. The middle dose group had more advantages than other dose groups. Milk yields of the middle dose group were significantly higher than other groups for 5 weeks (2w to 6w) after primary immunization.
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