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Uterine Capacity and Progestin Levels in Superinducted Gilts¹

North Carolina State University, Raleigh 27607

Abstract

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 (P<05) correlations between Day 13 progestin level and number of live embryos at Day 25 for the crossbred recipients (.67) and for the Yorkshire recipients (.65). These results indicate that progesterone levels on or near Day 13 of gestation may be associated with early gestation uterine capacity.

¹ Paper No. 4498 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh. Contribution from the Reproductive Physiology Research Laboratory, Department of Animal Science. Research supported in part by Special Grant Project No. 916-15-32 from the Cooperative State Research Service, U.S.D.A.

² Supported by a graduate research assistantship from the North Carolina Pork Producers. Present address: Department of Animal Science, University of Georgia, Athens.