Embryonic and placental development during prolonged inanition in the pig

Pregnancy is maintained in a high percentage (79%) of pigs subjected to inanition for periods up to 37 days, but few (25%) remain pregnant when inanition continues beyond 41 days. All remain pregnant during prolonged inanition (45 days) when exogenous progesterone and estradiol benzoate are given daily. Embryo survival rates in animals on inanition remain high (88%) and similar to those (89%) found in pigs given a full diet. Nitrogen content of embryos increases at a decreasing rate after 41 and 45 days inanition; placental nitrogen is markedly reduced at those times. By 45 days of inanition, nitrogen contents of embryos and placentas are less (P less than 0.01) than found in dams receiving a full diet. During prolonged inanition, exogenous progesterone (80 mg/100 kg) and estradiol benzoate (500 mug/100 kg) maintain embryonic and placental development at levels similar to those found in animals on a full diet. Maternal stores of protein and energy are made available for embryonic and placental developement in the presence of adequate levels of progesterone and estrogen, in spite of severe body weight loss during prolonged inanition of the dam.