Scientists studied milk from 15 different mammals—including humans, cows, and camels—to understand what invisible bacteria and helpful acids live inside it. They discovered that all mammal milk contains similar types of bacteria that help babies digest food and stay healthy. Interestingly, cow and horse milk have very similar helpful acids to human milk, which could be important for making better baby formula. The study also found that good bacteria produce special acids that fight off harmful germs, creating a natural protection system in milk that keeps newborns healthy.

The Quick Take

  • What they studied: What types of bacteria and helpful acids are naturally found in milk from different animal species, and how they work together to keep babies healthy.
  • Who participated: Milk samples from 15 different mammal species including humans, cows, horses, donkeys, yaks, camels, and buffalo. The exact number of milk samples wasn’t specified in the study.
  • Key finding: All mammal milk contains similar core bacteria, but the amounts and types vary by species. Cow and horse milk have nearly identical helpful acid profiles to human milk, suggesting they could be good alternatives for infant nutrition.
  • What it means for you: This research may help scientists create better baby formula that more closely mimics natural human milk. It also shows that the bacteria naturally present in milk play an important role in protecting babies from harmful germs and helping them digest food properly.

The Research Details

Researchers collected milk samples from 15 different mammal species and used two advanced laboratory techniques to analyze them. The first technique, called 16S rRNA sequencing, identifies and counts different types of bacteria present in the milk. The second technique, called GC-MS, measures the levels of special acids called short-chain fatty acids (SCFAs) that bacteria produce. By comparing the results across all 15 species, scientists could see which bacteria and acids were common to all mammals and which were unique to specific animals.

The researchers then looked for patterns—they examined whether the bacteria and acid levels were connected to each other and whether they related to things like the mother’s diet, her body temperature, or where she lived. This approach allowed them to understand not just what was in the milk, but why different species had different compositions.

Understanding what naturally occurs in milk is crucial for developing better infant nutrition products. By comparing multiple species, scientists can identify which components are essential for all mammal babies versus which are species-specific. This knowledge helps create formulas that better support infant digestion, immune system development, and overall health.

This study examined 15 different species, which is a comprehensive comparison. The use of two different laboratory techniques (genetic sequencing and chemical analysis) provides strong evidence. However, the study doesn’t specify exactly how many milk samples were tested from each species, which would help assess the reliability of the findings. The research was published in a peer-reviewed scientific journal, indicating it met professional standards for quality.

What the Results Show

The research revealed that all mammal milk contains three main types of bacteria at the broadest level: Firmicutes, Proteobacteria, and Actinobacteria. When looking more closely at specific bacteria types, three genera appeared most commonly: Pseudomonas, Lactobacillus, and Propionibacterium. This suggests these bacteria are fundamental to milk’s natural function across all mammals.

Human milk contained high levels of three helpful acids: butyric acid (12.94 units), valeric acid (0.12 units), and caproic acid (11.08 units). Remarkably, Holstein cow milk and Mongolian horse milk had very similar acid profiles to human milk, with cow milk showing 17.99 units of butyric acid and horse milk showing 15.21 units. This similarity is significant because these acids help babies absorb nutrients and develop healthy digestion.

The study also found that different species had bacteria suited to their environments. For example, yaks, camels, and buffalo living in hot or high-altitude regions had higher levels of a heat-loving bacteria called Thermus. Human milk uniquely contained higher levels of Rhizobium bacteria, possibly related to how mothers process glucose (sugar) in their bodies.

The research discovered important relationships between bacteria and the helpful acids they produce. Good bacteria like Bifidobacterium, Akkermansia, and Actinomyces showed positive connections with beneficial acids—meaning when these good bacteria were present, helpful acid levels were higher. Conversely, potentially harmful bacteria like Staphylococcus and Corynebacterium showed negative relationships with these acids, suggesting the acids naturally inhibit dangerous germs. This indicates milk has a built-in defense system where beneficial bacteria and their acid byproducts work together to prevent harmful bacteria from growing.

Previous research has shown that human milk contains beneficial bacteria and acids, but this is the first comprehensive study comparing these components across 15 mammal species. Earlier studies focused on individual species or smaller comparisons. This broader perspective confirms that certain bacterial types and acid profiles are conserved across mammals, supporting the idea that these components serve fundamental biological functions for infant development.

The study doesn’t specify how many milk samples were collected from each species or at what point in lactation (early, middle, or late) the samples were taken. Milk composition changes over time as mothers nurse, so this timing matters. The research also doesn’t detail the age, diet, or health status of the individual animals, which could influence results. Additionally, while the study identifies correlations between bacteria and acids, it doesn’t prove that one directly causes the other—only that they appear together.

The Bottom Line

Based on this research, cow and horse milk appear to have similar nutritional acid profiles to human milk and may serve as better bases for infant formula development (moderate confidence). Parents should continue following pediatrician recommendations regarding infant feeding, as this study provides foundational science rather than direct feeding guidance. For those interested in infant gut health, understanding that natural milk contains beneficial bacteria and protective acids supports the value of breastfeeding when possible (high confidence).

Parents and caregivers of infants should find this relevant, particularly those interested in understanding infant nutrition and formula development. Healthcare providers developing infant nutrition products should pay close attention to these findings. Pediatricians may find this useful for understanding the natural components of milk and infant digestive health. People with lactose intolerance or dairy sensitivities may be interested in understanding how different animal milks compare. This research is less directly relevant to older children and adults, though it provides general knowledge about dairy nutrition.

If these findings lead to improved infant formulas, benefits would likely be observed over weeks to months as infants’ digestive systems adapt and develop. Changes in infant digestion, stool quality, and overall health would be the first observable improvements. Long-term benefits to immune system development and reduced infections might take several months to become apparent.

Want to Apply This Research?

  • For parents of infants using formula, track weekly: infant digestion quality (stool consistency and frequency), any signs of digestive discomfort, and overall health markers like illness frequency. Rate each on a simple 1-5 scale to monitor patterns over time.
  • If using the app to monitor infant nutrition, users could log which type of formula or milk product is being used and correlate it with infant digestive health observations. This personal tracking helps identify which products work best for individual babies, since the research shows different milk sources have different compositions.
  • Establish a baseline of current infant health metrics (digestion, comfort, illness frequency) over 2-4 weeks. If switching to a new formula based on this research, continue tracking the same metrics for 4-8 weeks to observe any changes. Document patterns to share with pediatricians during regular check-ups.

This research provides scientific information about milk composition across species and is not medical advice. Parents and caregivers should consult with pediatricians before making any changes to infant feeding practices. While this study suggests cow and horse milk have similar acid profiles to human milk, this does not mean these milks are appropriate substitutes for human breast milk or specially formulated infant formula without professional medical guidance. Infants have specific nutritional requirements that must be met through appropriate feeding methods as recommended by healthcare providers. This information is for educational purposes and should not replace professional medical advice.