Morphological indications of secretion by uterine epithelial cells and changes in the ratio between acidic and basic uterine proteins during early pregnancy in Chinese Meishan pig.

In Chinese Meishan pig embryonic mortality appears relatively low compared to European breeds. Most of embryonic loss in pig is believed to take place during early pregnancy. It is of interest to know possible specific features associated with low mortality. Therefore, the ultrastructure of the endometrial epithelium of Meishan pig was studied between Days 4 and 12 of pregnancy, and compared with earlier results on Yorkshire/Dutch Landrace interbreed (Y/DL). Furthermore, total protein and the relative amounts of acidic and basic proteins were determined in the uterine flushings, and compared with earlier results on Dutch Landrace (DL). As holds for European breeds, uterine glandular and luminal epithelium have to be considered as functionally different cell populations. Their morphology differs and suggests the synthesis of different secretory products. The periods of secretion are not the same: the luminal epithelium shows signs of product release during the whole period studied, the glands deliver their secretions from Day 12. This is correlated with a sudden increase in total protein in uterine flushings. Between Days 4 and 12, the relative amount of acidic proteins decreases from 92% to 47% in DL and from 88% to 38% in Meishan, resulting in a shift from acidic protein dominance to a mild dominance of basic proteins in both breeds, but most prominent in Meishan.