Uterine capacity and progestin levels in superinducted gilts.

Embryos were transferred from crossbred donor gilts to eight Duroc, nine Yorkshire and eight crossbred recipient gilts to determine differences in uterine capacity among genetic groups. Donor gilts were injected IM with 750 IU of PMSG on Day 16 (onset of estrus = Day 0). Donors and recipients were mated 12 and 24 hr after onset of estrus. Embryos were recovered on Day 4 and were deposited into the uterus. Peripheral blood was collected from all recipients on Day 13 and Day 20 of gestation. Plasma progestin levels were measured, using radioimmunoassay, for all recipient gilts to determine the correlation between progestin levels and uterine capacity. Recipients were slaughtered on Day 25 + 2. The average number of corpora lutea and embryos deposited in the Duroc, Yorkshire and crossbred recipients were, respectively: .14.8, 13.1; 12.9, 13.3; 13.9, 15.6. The average number of normal embryos on Day 25 in the Duroc, Yorkshire and crossbred recipients was, respectively: 16.8 + 1.8; 18.1 + 1.3; 20.8 -+ 1.6. Although nonsignificant, (P>.05) there was a difference of four normal embryos between the Duroc and crossbred gilts. The average progestin concentrations (ng/ml plasma) on Day 13 and Day 20 for the Duroc, Yorkshire and crossbred recipients were, respectively: 22.8 +2.9, 21.7 + 2.0; 29.7 + 2.3, 19.2 + 1.2; 24.6 +1.3, 23.9 + 3.0. There were no differences (P>.05) in progestin levels among genetic groups. There were, however, significant