The placenta as a contributor to production of large calves.

Unusually high birth weights frequently occur in calves born from cultured bovine embryos. The mechanism(s) through which in vitro manipulations during early cleavage are translated to enhanced fetal growth is (are) incompletely understood. Accelerated growth is primarily prenatal, and the placenta of an in vitro-derived conceptus could account for abnormal fetal growth. Results from a systematic comparison of placental morphology and function in bovine concepti produced in vitro versus in vivo are discussed.