Breed differences in placental development during late gestation between Chinese Meishan and White crossbred gilts in response to intrauterine crowding

Authors: Miles, Jeremy; Vallet, Jeff

Submitted to: Animal Production Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2020
Publication Date: 3/1/2021
Publication URL: https://handle.nal.usda.gov/10113/7259950
Citation: Miles, J.R., Vallet, J.L. 2021. Breed differences in placental development during late gestation between Chinese Meishan and White crossbred gilts in response to intrauterine crowding. Animal Production Science. 226:106711. https://doi.org/10.1016/j.anireprosci.2021.106711.
DOI: https://doi.org/10.1016/j.anireprosci.2021.106711

Interpretive Summary: As litter size has increased in commercial swine production, there has been a consequential increase in preweaning piglet mortality as the result of greater within-litter birth weight variation and the production of smaller piglets due to limitations in uterine capacity and fetal crowding. Meishan pigs have large litter size and produce piglets that weigh significantly less than contemporary Western pig breeds but have reduced preweaning piglet mortality. The placenta has direct implications on uterine capacity, fetal growth, and survival as well as postnatal piglet growth and survival. To evaluate genotypic differences in placental development during late gestation following intrauterine crowding, this study performed unilateral hysterectomy ovariectomy in Meishan and White crossbred gilts to induce intrauterine crowding and evaluated both gross (histotrophic via glandular exchange) and microscopic (hemotrophic via capillary exchange) development of the subsequent placentas. Meishan placentas had greater density and improved development of placental areolae that regulate histotrophic exchange compared to White crossbred pregnancies, thereby demonstrating greater glandular exchange in Meishan pigs. In contrast, Meishan pregnancies had reduced influence of altered hemotrophic exchange (i.e. folded bilayer and placental stromal widths) between the smallest and largest littermate placentas compared to White crossbred indicating greater uniformity of blood exchange across the placentas of Meishan pigs. These alterations in placental development of Meishan pregnancies corresponded to decreased within-litter fetal weight variation compared to White crossbred pregnancies and provide potential mechanisms for reduced sensitivity of fetal growth in response to intrauterine crowding. Manipulation of these mechanisms may result in more uniform, vigorous piglets born in large litters and reduce preweaning mortality.

Technical Abstract: The objective of this study was to evaluate placental development during late gestation (day 100)between Chinese Meishan (CM; n = 7) and White crossbred (WC; n = 5) gilts following intrauterine crowding induced by unilaterally hysterectomy-ovariectomy. Gross placental morphology and areolae density as well as histological morphology (i.e., folded bilayer and placental stroma) were analyzed using computer-assisted morphometry for placentas of the smallest and largest fetuses within each litter. There was a breed by fetal size interaction (P < 0.01) for areolae density in which placentas for large CM fetuses had greater areolae density compared to small CM fetuses, but the density of areolae was greater for CM fetuses compared to WC fetuses, irrespective of fetal size. The width of the folded bilayer was greater (P < 0.01) in placentas for WC gilts compared to CM gilts, irrespective of fetal size. Placentas for small fetuses had greater (P < 0.01) folded bilayer width compared to large fetuses, irrespective of breed. The placental stromal width was greater (P < 0.01) in placentas for large fetuses compared to small, irrespective of breed. The difference between stromal width in placentas between divergent-sized littermates, however, was greater (P = 0.05) in WC gilts compared to CM gilts, indicating there was a limited response to intrauterine crowding in CM gilts. These results indicate there is an altered placental development during late gestation in CM compared to WC gilts, thus, there are likely different mechanisms for responding to intrauterine crowding between breeds.