EFFECT OF MATERNAL AGE ON VIABILITY OF OVA AND UTERINE SUPPORT OF PREGNANCY IN MICE

The technique of ova transplantation was used to study the causes of the decline in litter size in ageing mice. Only 14% of morulae and blastocysts obtained from the uteri ofyoung donors survived to term when transplanted into the uteri of old hosts (13 to 24 months of age), whereas 48% survived in young hosts (2 to 7 months of age). A slightly higher percentage of grossly abnormal ova was recovered on the 4th day of pregnancy from the uteri of old mice than from young mice (13% compared with 5%) However, normal-appearing morulae and blastulae from old mice survived as well as those from young mice when transferred into uteri of young hosts. It was concluded that the initial decline in litter size in aged mice is probably due to an unfavourable uterine environment.