Comparative studies of conceptus-endometrial interactions in Large White x Landrace and Meishan gilts

Uterine and conceptus function were compared in mated Meishan (MS) gilts and Large White x Landrace (LW x L) gilts (n = 18 breed-1) on Days 11-15, inclusive, after oestrus. Comparisons of individual blastocysts recovered on Day 11 and Day 12 revealed a higher overall embryo survival in MS gilts than in LW x L gilts (100.7 +/- 5.0% v. 69.5 +/- 12.1%; P < 0.05). Embryo survival was higher on Day 11 than on Day 12 (98.6 +/- 6.0% v. 71.6 +/- 12.6%; P < 0.05), with most of the embryo loss between these days occurring in LW x L gilts. MS conceptuses secreted less oestradiol-17 beta and radiolabelled protein on both days, but these differences were not significant. The within-litter variability in the secretion of oestradiol-17 beta and radiolabelled protein by individual conceptuses did not differ significantly between the breeds. Concentrations of epidermal growth factor in uterine rinsings were lower in MS gilts than in LW x L gilts on all days studied. However, two-dimensional polyacrylamide gel electrophoresis and fluorography did not provide evidence of additional breed differences in the profile of endometrial secretory proteins. Consistent temporal changes in the profile of the conceptus secretory proteins were observed among all LW x L gilts and among most of the MS gilts. However, conceptuses cultured from 2 of 5 Day-12 MS gilts secreted a major basic protein which was not evident in other conceptus cultures until Day 14. Similarly, antiviral activity was detected in some cultures of Day-13 MS conceptuses, but was absent from all Day-13 LW x L conceptus cultures. The results also revealed a positive relationship between ovulation rate and the incorporation of radiolabel into endometrial secretory proteins, which was independent of breed.