By Nanna M. Andersen | Published: 16.02.22 | Edited: 01.07.23
A summary of: Effect of Advanced Maternal Age on Pregnancy Outcomes and Vascular Function in the Rat By: Alison S. Care, Stephane L. Bourque, Jude S. Morton, Emma P. Hjartarson, Sandra T. Davidge. Hypertension (Dallas, Tex. : 1979), 65(6), 1324–1330. This study aims to investigate the impact of advanced maternal age on pregnancy outcomes and vascular function in rats. The research involves both young rats, aged between 3 and 4 months, and aged rats, aged between 9.5 and 10 months. The objective is to assess any potential impairment in vascular function in the offspring (Sengupta P.A). In comparison to the younger does, the aged does exhibited higher body weight and increased body fat during pairing. The aged does demonstrated a reduced ability to carry a viable pregnancy, with a success rate of approximately 48.2%, while the young does had an 89.5% chance of a viable pregnancy. Furthermore, the aged does displayed an overall decline in fertility, reduced litter size, increased resorptions, reduced fetal weight, and increased placental weight. Additionally, the aged does exhibited an elevation in maternal systolic blood pressure. Although the common litter size was 10-15 pups, the aged does had a significant number of single-pup litters in comparison to the younger does. Fetal resorptions were identified as the primary cause of small litters in aged does. The study also examined the myogenic response in the mesenteric artery, which reflects how arteries and arterioles respond to changes in blood pressure, maintaining a consistent blood flow within the blood vessels—an essential factor during pregnancy. Substantial differences were observed between young and aged females. The increased blood pressure in aged females was particularly notable, indicating a significant disparity compared to the young females. This finding correlates with the reduced litter size observed in aged females, as a smaller litter size ensures a more efficient blood supply to the developing fetuses. A summary of: Advanced maternal age compromises fetal growth and induces sex-specific changes in placental phenotype in rats By: Tina Napso, Yin-Po Hung, Sandra T. Davidge, Alison S. Care & Amanda N. Sferruzzi-Perri. Sci Rep 9, 16916 (2019). This study focuses on investigating the impact of placental phenotype on the growth of female and male fetuses using young rats aged between 3 and 4 months and aged rats aged between 9.5 and 10 months. Both groups are paired with males aged between 3 and 5 months. Similar to the previous study, various measurements such as litter size, pup weight, placenta weight, and more were recorded. In this summary, we will not repeat the specific results of this study, but instead emphasize the role of placental phenotype in supporting fetal growth. The findings of this study indicate that advanced maternal age alters the placental phenotype and its ability to support fetal growth. Specifically, it affects the morphological development of the placenta and the expression of genes and proteins that are crucial for placental growth, nutrient transfer, endocrine regulation of maternal physiology, and control of fetal glucocorticoid exposure. Advanced maternal age was found to induce oxidative stress and cell death in the placenta. Changes in gene expression in the placentas of female fetuses generally had beneficial effects, while changes in gene expression in the placentas of male fetuses were typically detrimental to placental growth and functional phenotype in aged dams. Both female and male fetuses showed growth restrictions. Furthermore, male fetal heart, brain, and liver weights were reduced in aged dams compared to young dams, with poorer cardiovascular outcomes observed in adult male offspring from aged dams. These findings suggest that male offspring from aged dams are more likely to experience poorer health as adults, which is significant for breeders as we consistently strive to ensure the longevity and well-being of our breeding lines. A summary of: Effect of advanced maternal age on development of hippocampal neural stem cells in offspring rats By: Y. Jing, H. Wei, L. Jie, Y. Chen, Z. Wen-Jie, S. Hong, P. Ya-Nan, C. Heng-Sheng, C. Li, J. Li. Chinese journal of contemporary pediatrics. 22. 1017-1026. This article examines the impact of maternal age on the development of hippocampal neural stem cells in rats. The study involves two groups of female rats: one group aged 3 months and another group aged 12 months. Both groups are bred to produce offspring, and a total of 40 offspring from each group are selected for evaluating the development of hippocampal neural stem cells. Although only a limited portion of the study's text is available, the results indicate significant differences in protein expression between the advanced maternal age group and the control group. Specifically, the advanced age group shows lower protein expression compared to the control group, while no significant differences in protein expression are observed between the two groups. The study suggests that advanced maternal age may have detrimental effects on the proliferation, survival, migration, and differentiation of hippocampal neural stem cells in offspring rats. These effects can potentially lead to developmental disorders in the hippocampal neural stem cells of the offspring. It emphasizes the importance of considering maternal age as a factor that influences the development of neural stem cells in the hippocampus of rat offspring. Further exploration of the article would provide more comprehensive insights into the methods used, additional results obtained, and the discussion surrounding the impact of advanced maternal age on hippocampal neural stem cell development in offspring rats. A summary of: Maternal age, reproduction and chromosomal aberrations in Wistar derived rats By: A. Niggeschulze & A. Kast. Lab Anim. 1994 Jan;28(1):55-62. This study focuses on the reproductive patterns and outcomes in rats of different age groups. A total of 20 virgin rats from various age groups (3, 6, 9, 12, and 18 months) were inseminated, resulting in 20 pregnant females in each age group. Table 1 presents data on the number of inseminated females in each age group. Notably, the 3, 6, and 9-month age groups exhibited success rates exceeding 80%, with 3-month-old females achieving an impressive 95% success rate. However, the success rates for aged females in the 12, 15, and 18-month age groups ranged from 10.5% to 57.7%. The study examines the number of corpora lutea, which are hormone-secreting structures formed in the ovaries after ovum release. Age group 18 had only 2 corpora lutea, while age groups 3 and 6 had 14.6 and 13.9 corpora lutea per female, respectively. This suggests that younger females produce a greater number of corpora lutea, providing more reproductive cells available for fertilization. Regarding the number of implantations, age groups 3 and 6 had over 200 live fetuses, while age group 9 had 86. The number of implantations decreased significantly in the 12-month age group. The resorption rate, calculated by subtracting the number of implantations from the number of live fetuses, was highest in age group 18 (100%), followed by age group 15 (96.3%) and age group 9 (51.4%). Age group 6 had a rate of 18.2%, while age group 3 showed a remarkably low resorption rate of 3.7%. The study highlights that rats, as prey animals, have evolved to reproduce at an early age to ensure species survival. However, fertility declines relatively early as well. Previous studies have reported a significant decrease in the number of embryos in females older than 12 months. These findings align with other research, which has also observed a 50% pregnancy rate for previously bred 12-month-old females and decreased litter sizes in females at 6 and 9 months due to lower egg production and higher implantation loss. In summary, this study provides insights into the reproductive patterns and outcomes in rats of different age groups. It emphasizes the influence of maternal age on implantation success, corpora lutea formation, and resorption rates. The findings contribute to our understanding of age-related reproductive changes and their implications for rat breeding programs. A summary of: Effects of advanced maternal age on cognitive and emotional development in offspring rats By: Wei Han, Xiangjun Dong, Xiaojie Song, Li Cheng, Lingling Xie, Hengsheng Chen, Li Jiang. Behav Brain Res. 2018 Nov 1;353:218-226. This article investigates the influence of advanced maternal age on the cognitive and emotional development of offspring rats. The study compares the offspring of young dams (3 months old) with those of aged dams (12 months old) using various behavioral tests. The study's results indicate that advanced maternal age significantly impacts the cognitive and emotional development of the offspring rats. Offspring from aged dams exhibit impaired spatial learning and memory performance compared to those from young dams. This suggests that advanced maternal age negatively affects cognitive functions related to spatial navigation and memory consolidation. Furthermore, the study reveals that the offspring from aged dams display increased anxiety-like behaviors, indicating altered emotional development. This suggests that advanced maternal age may contribute to emotional dysregulation in the offspring rats. These findings provide valuable insights into the long-term consequences of advanced maternal age on offspring development. Understanding the impact of maternal age on cognitive and emotional functions is crucial for comprehending the factors that influence offspring outcomes. Overall, the test results confirm that offspring from aged dams experience impaired development, including deficits in spatial learning, anxiety, depression-like symptoms, and social impairment. Delayed motherhood directly correlates with impaired development, including delayed sensorimotor integration, lower body weight, and reduced spontaneous motor activity in young adult offspring. A summary of: Maternal age and reproductive function in female Sprague-Dawley rats By: M. Ishii, T. Yamauchi, K. Matsumoto, G. Watanabe, K. Taya and F. Chatani. The Journal of toxicological sciences 37 3 (2012): 631-8. This study focuses on investigating the reproductive function of female Sprague-Dawley rats across different age groups, ranging from 6 to 40 weeks. The estrous cycle, which typically lasts around 4 to 5 days, was monitored throughout the study period, with cycles exceeding 6 days considered irregular. The findings shed light on the reproductive patterns of the female rats. At 9-10 weeks of age, the rats exhibited completely normal estrous cycles. However, as they reached 23-34 weeks of age, only 89% of them maintained a normal cycle, and this percentage further declined to 35% at 41-42 weeks of age. The main types of irregular estrous cycles observed at 23-24 weeks were prolonged cycles, where the females remained in heat for longer durations than usual. At 26-27 weeks of age, persistent diestrus was observed, indicating that the females were no longer receptive to the male's advances. The study also revealed significant findings regarding fertility and fetal development. At 26 weeks, a decline in fertility and implantation sites was observed, along with a decrease in the number of live fetuses. By 31 weeks, fetal growth retardation became evident. Based on these observations, the researchers concluded that the optimal age for breeding Sprague-Dawley rats falls between 8 and 22 weeks (approximately 2 to 5 months). The study highlights that the estrous cycle undergoes significant disturbances around 7.1 to 9.7 months of age, with initial irregularities observed around 5 to 6.2 months. These findings provide valuable insights into the reproductive timeline and fertility patterns of Sprague-Dawley rats, aiding researchers in determining the appropriate age for breeding and optimizing experimental designs. My conclusion The studies focuses on Wistar derived rats and I acknowledges that the findings may not translate exactly to our specific rat population with in the hobby. However, it provides valuable insights into the influence of maternal age on reproductive outcomes. The results suggest that advanced maternal age is associated with decreased success rates of insemination, reduced production of corpora lutea (hormone-secreting structures in the ovaries), lower numbers of implantations and live fetuses, and higher rates of resorption. These findings align with previous studies conducted on different rat lines and are likely applicable to our pet rats to some extent. The studies emphasizes the importance of considering maternal age in rat breeding programs and research studies. The observed decline in fertility and increased risk of chromosomal aberrations in older females highlight the need for careful management and selection of breeding pairs to optimize reproductive success and health of lines. In many countries, breeders typically start breeding a female rat when she reaches 4 to 6 months (17.4-26 weeks) of age. While ethical practices may vary, there is a general consensus that breeding females before 4-6 months is not ethically acceptable. Breeders who start breeding at 4-5 months (17.4-21.7 weeks) may experience larger litters, better weight gain in offspring, and improved social development compared to breeders who start breeding at 6 months or later. Breeding females later than 10 months of age may result in decreased litter size, reduced offspring weight gain, and deficits in social skills. The maximum breeding age is typically considered to be 18 months, but it is important to consider the potential negative effects on offspring. Therefore, it is logical to recommend to breed females for the first time between 3 and 5 months and for the last time before 10 to 12 months. Breeding females for a second time should be done cautiously to avoid straining the mother or risking the health of the offspring. High-risk pregnancies are observed in 15 and 18-month-old females, which provides a valid reason to avoid breeding females of this age. As responsible breeders, it is essential to prioritize the health of the rats and produce the healthiest offspring. The available evidence strongly supports the notion that breeding younger females is beneficial for both the offspring and the mothers. Some breeders may express concerns that females younger than 6 months are not psychologically mature enough to handle a litter because social maturity is not reached before 6 months according to one study. However, there is no scientific evidence to support the claim that rats are not psychological mature enough to handle a litter. In fact, studies have shown the opposite. Some concerns may stem from anthropomorphism or comparisons to other animals with slower development, such as cats or dogs. One valid reason to wait before breeding could be to evaluate the health of an unknown or previously problematic line. References:
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