Scientists studied how bacteria from a mother cow’s first milk (called colostrum) affects the bacteria living in a baby calf’s stomach and intestines. They tracked 42 calves from birth to 8 weeks old and found that about half of the bacteria in newborn calves came directly from their mother’s colostrum. Interestingly, even when calves were given antibiotics, their gut bacteria still developed normally over time. This research shows that a mother’s first milk plays a crucial role in building a healthy bacterial community in a calf’s digestive system, which is important for growth and health.

The Quick Take

  • What they studied: How bacteria from a mother cow’s first milk (colostrum) travel into and shape the bacteria living in a baby calf’s digestive system
  • Who participated: 42 mother cows and their newborn calves, tracked from birth through 8 weeks of age
  • Key finding: About 56% of the bacteria found in newborn calves’ intestines came directly from their mother’s colostrum, and roughly 37% of those bacteria were still present 8 weeks later
  • What it means for you: For farmers and veterinarians: colostrum (first milk) is critically important for establishing healthy gut bacteria in calves. Even when antibiotics are used for treatment, calves’ gut bacteria still develop normally over time, suggesting the natural seeding from colostrum is robust and resilient

The Research Details

Researchers collected first milk samples from 42 mother cows and then tracked the bacteria in their calves’ intestines at three time points: day 1 (birth), day 16, and day 57 (8 weeks). They used advanced genetic sequencing technology (Oxford Nanopore) to identify bacteria down to the species level—like being able to identify not just “dogs” but specific dog breeds. They also noted which calves received antibiotic treatments and compared how their bacteria developed compared to untreated calves.

This approach allowed scientists to trace where the bacteria in a calf’s gut came from and how the bacterial community changed as the calf grew. By sampling at multiple time points, they could see the progression from newborn to older calf and understand which bacteria stuck around versus which ones disappeared.

Understanding how calves’ gut bacteria develop is important because these bacteria help with digestion, nutrient absorption, and immune system development. By tracking bacteria from mother to calf, researchers can better understand what makes a healthy start in life. This knowledge could help farmers optimize colostrum feeding practices and understand how treatments like antibiotics affect long-term gut health.

This study used advanced genetic sequencing technology that can identify bacteria more accurately than older methods. The researchers tracked calves over time rather than just looking at a single moment, which provides better insight into how bacteria change. However, the study focused only on calves and their mothers, so results may not apply to other animals. The sample size of 42 cows is moderate—larger studies might reveal additional patterns.

What the Results Show

The bacteria in newborn calves’ intestines were quite different from those in older calves. On day 1, calves had relatively few types of bacteria, but by day 16 and day 57, the variety and amount of bacteria increased significantly. This is normal and healthy—a diverse bacterial community is generally better for digestion and health.

When researchers compared the bacteria in colostrum (mother’s first milk) to the bacteria in calves’ intestines, they found a strong connection. About 56% of the bacterial species found in newborn calves’ intestines on day 1 were also present in their mother’s colostrum. This shows that colostrum is a major source of the bacteria that colonize a calf’s gut. Even more impressively, about 37% of the bacterial species from colostrum were still present in the calf’s intestines 8 weeks later, suggesting these bacteria establish themselves for the long term.

The most common bacteria in colostrum were different from those in the calf’s intestines. Colostrum was dominated by bacteria called Paraclostridium, Romboutsia, and Staphylococcus, while newborn calves’ intestines had more Escherichia/Shigella and Clostridium. By day 16 and day 57, the calf’s intestinal bacteria shifted again, with Succinivibrio and Faecalibacterium becoming more abundant. This natural progression suggests the calf’s digestive system is selecting for bacteria that work best in that environment.

The study found that individual calves had quite different bacterial communities on day 1, but these differences decreased over time as all calves’ guts became more similar by day 57. This suggests that while colostrum provides an initial bacterial seed, the calf’s digestive environment gradually shapes the bacterial community toward a more consistent pattern. The researchers also noted that the three most common bacterial groups (Pseudomonadota, Bacillota, and Bacteroidota) were present in all samples—colostrum and calves at all ages—suggesting these are foundational bacteria for healthy calf development.

Previous research has suggested that early-life bacteria are important for calf health, but this study provides more detailed evidence of exactly how bacteria transfer from mother to calf and persist over time. The finding that colostrum is a major source of gut bacteria aligns with similar research in human infants, where breast milk bacteria also seed the baby’s gut. This study’s use of advanced sequencing technology allows for more precise identification of bacteria compared to older studies, providing a clearer picture of this bacterial transfer.

This study focused only on calves and their mothers, so the findings may not apply to other animals or species. The researchers didn’t provide detailed information about all the factors that might affect bacterial development, such as the exact diet each calf received or specific environmental conditions. The study also didn’t measure whether differences in bacterial communities actually affected calf health outcomes—it only tracked which bacteria were present. Additionally, while the study included calves that received antibiotics, the number of treated versus untreated calves wasn’t clearly specified, which limits conclusions about antibiotic effects.

The Bottom Line

For farmers and veterinarians: Ensure calves receive adequate colostrum (first milk) from their mothers as soon as possible after birth. This appears to be the primary way healthy bacteria establish themselves in a calf’s gut. The research suggests that even when antibiotics are necessary for treating infections, the natural bacterial seeding from colostrum is resilient enough to support normal gut development. Confidence level: Moderate to High—this finding is supported by the data, though more research on health outcomes would strengthen recommendations.

This research is most relevant to farmers raising cattle, veterinarians treating calves, and researchers studying animal health. It may also interest people studying human infant health, since similar processes occur in human babies. This research does not directly apply to people—it’s specific to cattle.

Changes in calf gut bacteria happen relatively quickly. The most dramatic changes occur between day 1 and day 16, with further development continuing through day 57 (8 weeks). Farmers should expect the bacterial community to stabilize by 8 weeks of age, though continued development likely occurs beyond this timeframe.

Want to Apply This Research?

  • For farmers using a livestock management app: Track colostrum feeding timing and volume for each calf at birth, then monitor calf health metrics (weight gain, digestion issues, illness) weekly for the first 8 weeks to correlate colostrum quality/timing with health outcomes
  • Implement a daily checklist in the app to confirm: (1) colostrum was fed within 2 hours of birth, (2) adequate volume was provided, and (3) calf showed normal digestion in the following days. This ensures best practices for bacterial seeding
  • Create a long-term health dashboard tracking calf growth rate, disease incidents, and antibiotic treatments through the first 8 weeks, allowing farmers to identify patterns between colostrum practices and health outcomes across their herd

This research describes bacterial patterns in calves and does not constitute veterinary medical advice. Farmers and livestock managers should consult with their veterinarian regarding colostrum feeding practices, antibiotic use, and calf health management. While this study suggests colostrum plays an important role in bacterial development, individual calf health depends on many factors including genetics, nutrition, environment, and disease exposure. This research applies to cattle only and should not be extrapolated to other species without additional evidence.