Scanning electron, light optical, and transmission electron microscopy and plasma steroid values of porcine uterus at lactation.

Sows, while nursing litters for a period of 4 to 8 weeks, do not ovulate, thereby delaying the time sows can be rebred. Therefore, this study sought to determine how soon after parturition the morphological appearance of the uterus was such that blastocyst implantation could possibly proceed. Biopsy samples taken immediately post-partum and on days 1, 2, 3, 4 post-partum show that the endometrium was considerably damaged as evidenced by sloughing of the zona compacta and zona spongiosa and the presence of leukocytes around the surface epithelial (SE) cells. Around the 6th day post-partum the numbers of leukocytes were reduced and regeneration of the SE was evident. Around the 8th day post-partum, SE cells appeared similar to those of normal cyclic sows in the late luteal phase (i.e. 15 days post-estrum). Under normal breeding conditions, blastocyst implantation takes place during the late luteal phase. From 17 to 26 days post-partum the SE cells appeared similar to those of normal cyclic sows in the early follicular phase (i.e. 21 days post-estrum), and the subepithelial layers seemed edematous. Estradiol and progesterone concentrations dropped markedly at parturition and remained low up to the 26th day of lactation. Although there was considerable heterogeneity of samples between sows it was concluded, from the morphological results, that plasma steroid levels exert relatively little effect on the sow endometrium up to 26 days post-partum. If ovulation could be induced or ova transplant be performed in lactating sows the endometrium would appear ready for blastocyst implantation after day 8 post-partum.