Effects of maternal environment during gestation on ovarian folliculogenesis and consequences for fertility in bovine offspring.

Mammals such as cattle, swine, sheep and humans are born with a highly variable number of ovarian follicles and oocytes in the ovaries that dwindle during ageing and are never replenished. This variation in the ovarian reserve is reflected in the numbers of antral follicles in the ovaries at all ages after birth. As numbers of follicles in ovaries are determined during gestation, the role of maternal nutrition and health during gestation (at time of ovarian development in their foetuses) has been investigated as factors that may impact oogonia proliferation and thus follicle numbers post-natally. These studies have found that both nutrition and health impact numbers of follicles in their offspring. The idea that numbers of follicles and oocytes in ovaries impact fertility is a long-held belief in reproductive biology. This has recently been tested in cattle, and it has been shown that cows with a relatively high number of antral follicles in ovaries have higher pregnancy rates, shorter calving to conception intervals and fewer artificial inseminations during the breeding season compared with cows with a lower number of follicles, and similarly, heifers with many follicles had higher pregnancy rates than those with fewer follicles. Studies summarized in this review highlight the importance of the maternal environment during gestation in determining the size of the ovarian reserve in their offspring and also the contribution of the ovarian reserve to subsequent fertility in cattle.