Energy allocation during concurrent pregnancy and lactation in Norway rats with delayed and undelayed implantation
✍ Scribed by Oswald, Christine ;McClure, Polley Ann
- Publisher
- John Wiley and Sons
- Year
- 1987
- Tongue
- English
- Weight
- 1000 KB
- Volume
- 241
- Category
- Article
- ISSN
- 0022-104X
No coin nor oath required. For personal study only.
✦ Synopsis
Despite the high cost of lactation alone, concurrent pregnancy and lactation (CPL) is widespread among rodents. Many species that exhibit CPL delay implantation of the litter in utero while nursing. The first purpose of this study was to describe the pattern of energy allocation during CPL in a species with a large degree of overlap between gestation and lactation. Resting metabolic rate, food consumption and mass changes of Norway rat dams and litters, digestive efficiency and urinary energy loss of dams, and pup tissue energy equivalents were determined for CPL dams and for dams that were only lactating (C). CPL dams had significantly higher metabolic rates than C dams. Food consumption, pup growth, tissue energy equivalents, and assimilation efficiency were similar for both groups. The energy equivalent of mass change was greater for C dams, which gained in maternal mass (lipid) during lactation, than for CPL dams, which only increased in mass because of the litter in utero. The second purpose of this study was to investigate the suggestion that delayed implantation during CPL evolved as a mechanism to lower peak energy demands during CPL. Concurrently pregnant and lactating dams were injected with estrone (ECPL dams) on days 3-16 of lactation to prevent them from delaying implantation. A group of dams that were only lactating also received estrone injections (EC dams). ECPL dams produced smaller offspring at weaning than EC dams. This effect was more pronounced for largelittered dams. These results indicate that the increased metabolic cost of a concurrent pregnancy is met by diverting energy into production of pup tissue rather than maternal tissue and that delayed implantation likely evolved as a means to decrease the peak energy demands of CPL.