Milk is often viewed simply as a source of nutrition, but it is also a biologically active fluid that reflects the health of the cow producing it. New research published in Animal Nutriomics sheds light on the immune cells found naturally in cow’s milk, and why they matter for both animal health and milk quality.

In this study, researchers set out to better understand the biology of the mammary gland, the tissue responsible for milk production. By examining milk at the level of individual cells, the team aimed to uncover how immune function within the mammary gland supports healthy milk production and overall cow wellbeing.

Looking Inside Milk One Cell at a Time

Using a powerful technique known as single-cell RNA sequencing, the researchers analysed fresh milk samples from healthy Holstein cows. This technology allows scientists to study individual cells in great detail, including rare or low-abundance cell types that are often missed by traditional methods.

The analysis revealed that immune cells are a major component of cow’s milk, with T cells and granulocytes identified as the most common immune cell types in healthy animals. These cells play important roles in immune defence, helping protect the mammary gland from infection while supporting normal milk production.

By mapping these immune cell populations, the researchers gained new insights into how the mammary gland maintains immune balance, a key factor in both cow health and milk quality.

Why Mammary Immune Health Matters

The immune system of the mammary gland does more than just fight disease. It helps maintain tissue health, supports milk secretion, and influences the biological quality of milk. Understanding which immune cells are present and how they function, can help scientists identify early signs of imbalance or disease, even before clinical symptoms appear.

As lead author Gabriela Perez-Hernandez of Virginia Tech explains:

“Our study highlights the presence of immune and secretory mammary cells in cow milk and underscores their significance for understanding mammary gland function and health. Our findings lay the groundwork for future studies aimed at uncovering the molecular mechanisms that influence milk production and glandular health.”

Improving this understanding could lead to new strategies for supporting cow health, reducing disease risk, and enhancing milk quality through better management and nutrition.

Advancing Sustainable Milk Production

The study also highlights the growing importance of advanced technologies like single-cell RNA sequencing in animal science. By enabling researchers to examine milk at unprecedented resolution, these tools are transforming how we study livestock biology.

Importantly, this work contributes to broader efforts to improve the sustainability and efficiency of dairy production. Healthier cows produce higher-quality milk, require fewer medical interventions, and contribute to more resilient farming systems, benefiting both the agricultural industry and human nutrition.

As Perez-Hernandez notes, this research supports “more sustainable and efficient milk production practices, with potential benefits for both the agricultural industry and human nutrition.”

About the Study

The six-month, non-invasive study took place at the Virginia Tech Dairy Science Complex in Blacksburg, Virginia, where cows remained part of the regular milking herd throughout. The research was conducted by a team here, using milk samples from 25 healthy Holstein cows at different stages of lactation, milk yield, and pregnancy.

Read the open access article in Animal Nutriomics
Characterization of Cellular Heterogeneity in Milk from Healthy Bovine Mammary Glands
G. Perez-Hernandez, A. J. Lengi, M. Makris & B. A. Corl (2024)

Read the full news story here: Good immune functions could enhance cow milk quality and health