Effects of Litter Size on Gestation Length and Plasma Progesterone Concentration in Mongolian Gerbils (Meriones unguiculatus)
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A total of 31 female Mongolian gerbils (19-54 weeks of age at mating) were used for this study. The mean litter size at birth in all females was 4.4±0.3, ranging 1 to 8 pups. Although maternal age did not affect to litter size and gestation length, litter size did significantly to gestation length. Plasma progesterone (P<sub>4</sub>) was measured in serial blood samples collected every 3 days throughout gestation period. The P<sub>4</sub> concentration increased rapidly after mating, reaching a peak level on day 6 of gestation, maintained the high level to day 12 of gestation, then decreased to a moderate level and sustained at the level until day 21. The P<sub>4</sub> concentration decreased to a lowest level on day 24 of gestation (mean gestation length: 25.2 days). Females having a large number of litter size tended to reveal higher level of P<sub>4</sub> during gestation, comparing with that females having a fewer litter size, and significant differences between them were found on days 6 and 9 of gestation. There were significant differences in P<sub>4</sub> levels among 3 groups according to gestation length, resulting in lower P<sub>4</sub> level from females with longer gestation length. Therefore, difference of plasam P<sub>4</sub> level during the gestation is due to litter size.
- Nihon Chikusan Gakkaiho
Nihon Chikusan Gakkaiho 70(1), 18-23, 1999-01-25
Japanese Society of Animal Science