Main takeaway: the first microbes a puppy or kitten meets may matter more than we used to think. Perinatal microbiota could become an important part of preventive veterinary care — but only if future recommendations are built on strong evidence, not assumptions.

A new review in Frontiers in Veterinary Science looks at something that may become increasingly important in veterinary medicine: the perinatal microbiota in dogs and cats.

In simple terms, the authors explore how early microbial exposure — before birth, during birth, and in the first weeks of life — may influence neonatal health and future development.

One of the key points is that there is still no convincing evidence that healthy puppies or kittens have a viable microbiota before birth. Low amounts of bacterial DNA can be detected in fetal samples, but living bacteria have not been found in amniotic fluid during healthy pregnancies. Colonization appears to begin mainly at birth.

This does not mean the maternal microbiome is irrelevant during pregnancy. Maternal gut microbiota may still shape fetal development through metabolites and epigenetic mechanisms, for example via short-chain fatty acids that can cross the placental barrier.

The review highlights several factors that shape early microbiota:
• the health and nutrition of the mother
• delivery mode and birth environment
• early colostrum and milk intake
• maternal contact and care
• antibiotic use
• possible probiotic or prebiotic interventions

For puppies, the dam’s vaginal microbiota seems especially important for the first microbial exposure at birth. In one study, the newborn gut microbiota matched the dam’s vaginal microbiota by around 72%. Natural delivery may support better vertical microbial transmission, while C-sections, excessive hygiene, unnecessary antibiotics, or artificial rearing may alter early colonization patterns.

The authors also stress that colostrum is not only about passive immunity. It also provides microbes, immune factors, oligosaccharides, and bioactive compounds that help shape the neonatal gut ecosystem.

There are already some encouraging early findings in dogs. Supplementing pregnant dams with the probiotic yeast Saccharomyces cerevisiae var. boulardii helped stabilize the maternal microbiota, increased short-chain fatty acid–producing bacteria, and was associated with fewer low-birth-weight puppies and more even growth.

Importantly, the authors note that not all probiotics are equivalent. Effects are strain-specific, dose-dependent, and context-dependent. Human-targeted formulas should not simply be used in animals; interventions need to be tested and proven for the species and situation.

For veterinary practice, the message is cautious but promising: we should not rush into unproven interventions such as vaginal seeding or neonatal fecal microbiota transplantation. Instead, the current focus should be on evidence-based basics — healthy dams, stable high-quality nutrition, avoiding unnecessary antibiotics, supporting natural birth when medically possible, ensuring early colostrum intake, and monitoring at-risk neonates.

The biggest gap is still research. Data in dogs are emerging, but in cats they remain very limited. Much of what we assume about kittens is still extrapolated from other species rather than directly studied.

Original article: Banchi et al. (2026), The perinatal microbiota in dogs and cats: a narrative review from human research to veterinary practice, Frontiers in Veterinary Science. DOI: 10.3389/fvets.2026.1817504. Licensed under CC BY 4.0.