Effect of Simulated Microgravity on Sexual Development of Female Japanese Quail

Škrobánek P., M. Baranovská, B. Šárniková, M. Juráni: Effect of Simulated Microgravity on Sexual Development of Female Japanese Quail. Acta Vet Brno 2008, 77: 3-10. Hypodynamia is a method to simulate weightlessness (microgravity) in the laboratory conditions. The objective of this study was to investigate the influence of chronic hypodynamia on the growth and development of the ovary and oviduct, plasma estradiol and progesterone concentration, and the onset of egg-laying in Japanese quail. The ovary weight gradually increased with age in both groups. However, the experimental birds subjected to hypodynamia showed a significant reduction in ovary weight relative to agematched control between 21 and 42 days of age (P < 0.05). The number of yellow follicles with a diameter of less than 10 mm, between 10 and 15 mm and more than 15 mm was similar in both groups from 49 days to the end of experiment. The control birds had significantly longer oviduct than those of the test group from 28 to 63 days (P < 0.05) with the exception of day 49. The quail reared under hypodynamia laid their first egg about three days later than control. Plasma progesterone concentration in experimental quail was significantly reduced between 28 and 49 days (P < 0.05). Plasma estradiol concentration increased progressively with age in both groups. The differences between the groups were not significant at any age. These findings suggest that although hypodynamia negatively affects some of the examined variables, the female Japanese quail is able to grow and develop normally under conditions of simulated weightlessness. Hypodynamia, ovary, oviduct, progesterone, estradiol Since the Earth’s gravitational field has remained constant for billions of years, it is assumed that gravity plays a substantial role in the ontogeny of organisms. By means of experiments in weightless environment (microgravity), we should be able to answer questions on the importance of gravity for the development of organisms. Numerous authors have successfully studied different phases of embryogenesis in insects, fishes, amphibians, birds and mammals in microgravity during space flights. It was found, for example, that Japanese quail embryogenesis does not appear to be seriously affected by the conditions of weightlessness (Guryeva et al. 1993; Dadasheva et al. 2001). In experiments aboard the MIR space station, Japanese quail embryos successfully completed embryogenesis and hatched chicks had all the external characteristics of healthy development (Boďa et al. 1992; Sabo et al. 2001). How microgravity may influence further development of quail chicks is unknown. However, partial answer may be obtained by ground-based animal models simulating microgravity (hypodynamia). The first experiments with hypodynamia in birds were carried out in the adult Japanese quail (Juráni et al. 1983). Twenty years later, the first experiment examining the adaptability of newly hatched Japanese quail chicks to hypodynamia was accomplished (Škrobánek and Hrančová 2003). In further experiment, the post-hatch development of Japanese quail subjected to hypodynamia from 3 to 56 days of age was studied (Škrobánek et al. 2004, 2005). The objective of this study was to examine the effects of hypodynamia on development of the ovary and oviduct, the plasma concentrations of estradiol and progesterone, and the onset of egg-laying in Japanese quail. ACTA VET. BRNO 2008, 77: 03–10; doi:10.2754/avb200877010003 Address for correspondence: Ing. Peter Škrobánek, CSc. Institute of Animal Biochemistry and Genetics Slovak Academy of Sciences Moyzesova 61 900 28 Ivanka pri Dunaji, Slovak Republic Phone: + 421 02 45 943 881 Fax: + 421 02 45 943 932 E-mail: [email protected] http://www.vfu.cz/acta-vet/actavet.htm Materials and Methods Seventy 3-day-old female Japanese quail (Laying Line 01 Ivanka pri Dunaji) with mean body weight 10.56 ± 0.42 g were exposed to hypodynamia. Hypodynamia, model simulating weightlessness characterized by the absence of weight-bearing and by a decrease in motor activity (Morey et al. 1979) was modified in our laboratory for the use in birds (Škrobánek et al. 2004). Hypodynamia was induced in birds by placing them in special individual slings suspended by a flexible wire apparatus in such a way that their legs cannot touch the floor. The size of the slings was enlarged at 7, 14, 21, 28 and 35 days of age (from 4 × 3 cm to 5 × 4 cm to 6 × 5 cm to 7 × 6 cm and 8 × 7 cm) to accommodate the growth of the quail. At the same time, seventy quail chicks (control group) were placed in a rearing box (120 × 60 × 30 cm). The birds of both hypodynamia and control group were kept until 63 days of age in a windowless poultry room with controlled ventilation and heating (infrared lamps). The temperature in the rearing room was maintained at approximately 35 – 36 °C for the first few days after hatching, then decreased gradually during four weeks to about 20 °C and remained at this level until the end of experiment. A commercial starter mash HYD-13 and water were available ad libitum. The granular diet containing 260 g/kg protein and 11.5 MJ metabolisable energy/kg was fed from the hatch to the termination of experiment. Birds were provided with continuous lighting throughout the whole experiment. The care and use of animals were in accordance with laws and regulations of the Slovak Republic and approved by the Ethical Committee of the Institute of Animal Biochemistry and Genetics, Slovak Academy of Sciences, Ivanka pri Dunaji. At 21, 28, 35, 42, 49, 56 and 63 days of age, ten birds were randomly selected from hypodynamia and control group for the assessment of the degree of their reproductive development. Birds were individually weighed and euthanized by decapitation. The blood samples were collected from a jugular vein using heparinised glass tubes and centrifuged at 1500 g for 30 min at 4 °C to separate the plasma. The plasma was stored at -20 °C until estradiol and progesterone radioimmunoassay (Immunotech, Slovakia) was performed. Decapitation and blood collection was always carried out between 8:00 and 9:30 h. Immediately after blood collection, the abdominal cavity was opened; the ovary was removed and weighed. The number of yellow ovarian follicles (with diameter < 10 mm, between 10 and 15 mm, and > 15 mm) was recorded. The left oviduct was dissected and its length measured. The age of sexual maturity (the first egg) of the remaining hens was also recorded. Data from both groups were analyzed by two-way analysis of variance (ANOVA) with the age and treatment as factors. In each analysis, significant differences among means were detected using Tukey multiple comparison test. In all cases the level of significance was set at P < 0.05. All values are presented as mean ± SEM.