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 p 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.
