Canine Placenta Histological Findings and Microvascular Density: The Histological Basis of a Negative Neonatal Outcome?

Abstract

Placenta is essential for the development of the fetus, and its impaired function can lead to a negative outcome (i.e., neonatal mortality). In dogs, investigations on placenta histology and neonatal outcome in healthy bitches are lacking, and a contribution is provided in this study to emphasize the use of placenta histology in practice. Fifty-one placentas from 11 litters were collected during cesarean section, classified according to the litter size (large (L) or small (S)) and the outcome, this latter as healthy (Group 1) or dead within 7 days (Group 2). The placenta/puppy weight ratio (PPR) was calculated, and specimens were formalin-fixed and paraffin-wax embedded, and on the resulting histological slides, capillary density (CD) was quantified. Among necrosis, calcification, and intravascular leucocytes, only the presence of multifocal-confluent necrosis (significantly more frequent in Group 2) was associated with a higher risk of death within 7 days (odds ratio = 30.7). Mixed logistic regression ruled out the effect on death both of a bitch and cesarean type (programmed vs. emergency). PPR and CD values were associated with litter size; large litters had lower PPR (p < 0.01) and higher CD (p < 0.05) than small litters. The relationship between PPR and CD was negative and significant (p < 0.01). Necrosis was a frequent finding in canine placentas, but only when multifocal-confluent was it associated with a poor outcome. The litter size influenced PPR (lower in L) and CD (higher in L), and this is likely due to the plasticity of placenta adaptation.

Collagen and Microvascularization in Placentas From Young and Older Mares

“…The increased vascularization in the gravid horn might have been a compensatory feature to provide the appropriate nutrition to the equine fetus. In the bitch, the lowest ratio of placenta weight and puppy weight occurs in larger litters and when placentas depict the highest capillary density, with respect to smaller litters ( 14 ). In older mares, the highest ratio of placenta weight and foal weight was associated with more parturitions, and placentas that presented the highest vascular density, which might show an adaptation of the placenta and increased efficiency with parity, as referred ( 51 ).…”

“…It is well known that intrauterine fetal nutrition influences both foal's health (7,8), and its athletic performance (9,10). Nevertheless, regardless of the animal species, the macroscopic examination of the placenta does not reveal microscopic lesions that are only detected by histological examination or electron microscopy observation, and that might be related to fetal death, neonate low body weight or sickness (11)(12)(13)(14).…”

“…In fact, during mare gestation, besides morphological alterations, and degenerative changes in the microplacentomes on the surface of the mare placenta, also the development of fetal and maternal capillary beds within each microplacentome is diminished, disturbing physical and hematological contact at the fetomaternal interface, and hence impairing fetal growth ( 13 , 18 ). In other species, vascularization of the placenta is also extremely important, as in the sow ( 11 ), bitch ( 14 ) and in woman ( 19 ). In fact, in humans, reduced vasculature of the placenta is frequently related with intrauterine fetal growth restriction ( 19 ).…”

“…A body of evidence shows that in a number of species, deficiencies in placental structure and function can be reflected in impaired fetal development and growth with the decrease in neonates birth weight ( 13 , 14 , 18 , 27 ). Therefore, we have put forward the hypothesis that as mares age, fibrosis increases in the placenta, and microvascularization decreases, leading to a reduction in foal weight.…”

Dead or Alive? A Review of Perinatal Factors That Determine Canine Neonatal Viability

“…Numerous studies have been carried out on human and other animal species that provide information on the relation between the birth weight and placenta [ 117 , 118 , 119 , 120 , 121 ]. Several studies were conducted on dogs [ 113 , 122 ]. In small and toy breeds, authors revealed a positive correlation between the birth weight of a puppy and the placental weight and its total area [ 113 ].…”