One Child Every Child study explores how donor human milk may protect babies’ developing microbiome

In the first hours after a baby is born, everything feels fragile and beautiful. There is the weight of new life in a mother’s arms. The quiet calculations of nurses. The hope that breastfeeding will unfold naturally. And, sometimes, the unexpected reality is that it doesn’t.

For decades, when supplementation was needed in the early days postpartum, formula was often the only option. But a team of researchers with the University of Calgary's One Child Every Child DO-RE-MI (DOnor human milk to REpair the infant MIcrobiome) study is asking a different question: If exclusively breastfeeding shapes the infant microbiome in powerful, unique ways, could pasteurized donor human milk do the same when mothers need supplementation support? 

In Canada, pasteurized donor human milk is provided through regulated milk banks such as NorthernStar Mothers Milk Bank.

The supplementation landscape is changing 

Science tells one story; mothers add the context and human elements that create change.

“A consistent theme emerged: donor milk alleviates guilt for moms when they have to supplement,” says Dr. Meredith Brockway, BN’04, PhD’09, an assistant professor in the Faculty of Nursing who is leading the study. 

For motivated families who want to breastfeed, offering donor milk can transform the experience to one of support.

“Having donor milk meant I could breathe,” shared one mother participating in the study. “I knew my baby was getting human milk, and I had time for my body to catch up. It changed everything.”

Exclusive breastfeeding has long been understood to buffer many early exposures such as antibiotics, C-sections and hospital environments.

A blank slate and the critical window

A baby’s microbiome begins as a blank slate. Babies born vaginally are naturally exposed to helpful bacteria that begin building a healthy gut microbiome from birth. In the months that follow, feeding patterns shape that ecosystem. As the microbiome develops over the first two to three years of life, it influences immune protection, metabolism, even neurotransmitter pathways such as serotonin production which is mostly produced in the GI tract. 

Breastfed infants have lower risks of asthma and other immune-mediated conditions. Brockway and her team are increasingly uncovering the mechanism: Bacteria in the gut are not passive passengers; they participate in the body’s biological pathways.

“We are exploring if donor human milk can help restore the infant microbiome in the same way that exclusive breastfeeding does, if mothers are required to supplement while breastfeeding,” says Brockway.

The trials: Antibiotics and the microbiome, C-section birth and feeding patterns

Brockway and her team have completed microbiome analyses for their first pilot randomized controlled trial comparing donor human milk to formula supplementation in vaginally born, full-term infants exposed to antibiotics during labour. These findings are now being rigorously evaluated. Protocols for the study are published in Sage Choice.

Once the analysis is complete, researchers expect the study will provide unprecedented evidence on how exclusive human-milk feeding compared to formula supplementation shapes the developing microbiome in infants whose earliest bacterial exposure has already been disrupted, laying the scientific foundation for feeding decisions that have long relied more on intuition than evidence.

Building on this work, their second pilot trial recently recruited its 150th participant, focusing on full-term infants born via C-section. Early findings reveal striking differences in supplementation patterns compared to vaginal births, likely reflecting the well-documented breastfeeding challenges following surgical delivery. Supplementation peaks on days two to three as families leave hospital and maternal milk supply is still being established; approximately 60 per cent of C-section mothers supplement, compared to about 40 per cent of vaginal-birth mothers.

With no published Canadian data capturing these granular early supplementation patterns, this research begins to fill a critical national gap, raising important questions about hospital-based breastfeeding supports and the accessibility of donor milk for families who need it most.

Partnership with One Child Every Child

“We’re proud to partner with Dr. Brockway,” says Donna Gersbach, executive director of NorthernStar Mothers Milk Bank. “As Canada’s only community-based milk bank, we see firsthand how her research is informing clinical improvements in how donor milk is used, strengthening care for infants and families across the country.”

The central question now is: Can donor human milk help restore microbiome trajectories in vulnerable infants when exclusive breastfeeding is temporarily out of reach?

For the first time in Canada, evidence is being built to answer that question.

And, in the quiet, tender days after birth, that answer could change everything.

The study was published in PubMed.

For information on donating to the Northern Star Mothers Milk Bank, visit the website.