Animals and Tissue Collection
Investigations were conducted in accordance with the Guiding Principles for the Care and Use of Research Animals promulgated by the Society for the Study of Reproduction.
White crossbred (WC) gilts (1/4 Yorkshire, 1/4 Large White, 1/4 Chester White, and 1/4 Landrace) were unilaterally hysterectomized and ovariectomized at approximately 160 days of age using previously described procedures. Twenty WC UHO, 17 WC normal (intact: INT), and 23 MS gilts were observed for behavioral estrus once daily. After at least one estrous cycle of normal length, WC (INT and UHO) gilts (age 262-320 days) were bred. Because of earlier onset of puberty and increases in ovulation rate up to the sixth estrous cycle, MS gilts (age 272-308 days) were not bred until after their seventh estrous cycle. Pregnant gilts of each treatment group (INT, UHO, and MS) were slaughtered on either Day 24, 30, or 40 of pregnancy. birth control pills
At slaughter, a maternal blood sample (mixed arterial and venous; approximately 20 ml/gilt) was collected in a 50-ml polypropylene tube containing 1 ml (600 U) heparinized saline. The reproductive tract was removed, the entire length of the uterus was opened along the antimesometrial surface, and blood samples were collected from the umbilical vessels (mixed arterial and venous blood) of each embryo/fetus (for simplicity, embryos and fetuses are hereafter referred to as “fetus,” with “fetal” used as a descriptive term) in heparinized syringes. Fetuses were then removed and weighed, and liver tissue from one fetus/gilt was collected for explant culture. Placentae were then removed and weighed, and corpora lutea were counted. Blood smears were made from 2-3 individual fetal blood samples per gilt, and remaining blood samples from Day 24 or Day 30 fetuses from the same gilt were pooled for subsequent analysis because of low volume of blood collected. Fetal survival percentages were calculated by dividing the number of live fetuses (presence of heartbeat, robust appearance) by the number of corpora lutea X 100.