Is There Blood and Mucus in Cow Milk?

January 13, 2026 •

4 min read

While milk in a healthy cow should not contain blood or mucus, dairy cows with a common udder infection called mastitis can produce milk with these contaminants. The good news is that stringent testing and regulatory oversight in the dairy industry prevent contaminated milk from reaching consumers.

Quick Summary

Milk from an infected cow may contain blood, mucus, or pus due to mastitis, but industry regulations and testing ensure retail milk is safe. The presence of these substances signals a serious health issue for the animal, which is addressed by farmers and processors to prevent contamination of the overall milk supply. Milk with high somatic cell counts from mastitis is discarded.

Key Points

Mastitis is the primary cause: The presence of blood or mucus in raw cow milk is a sign of mastitis, an inflammation of the udder caused by bacterial infection.
Retail milk is safe: Strict dairy industry regulations and testing procedures prevent milk from infected cows from entering the commercial supply.
Somatic Cell Count (SCC) is monitored: Bulk milk is tested for SCC levels; high counts indicate infection, and the milk is rejected.
Trauma can cause blood: Physical injuries to the udder or teats can cause capillaries to break, resulting in blood in the milk.
Hygiene prevents contamination: Proper milking and housing hygiene are crucial for preventing mastitis and ensuring clean milk.
Contaminated milk is discarded: Farmers identify and discard milk from infected cows before it can be mixed with the general supply.
Pasteurization kills pathogens: Heating milk during pasteurization eliminates any bacteria, though it does not remove contaminants.

The Truth Behind Blood and Mucus in Raw Cow Milk

The idea that cow milk might contain blood or mucus can be unsettling. The key distinction is between raw, unprocessed milk from a sick animal and the pasteurized, tested product you purchase at a store. The primary reason a cow's milk might contain these substances is an infection known as mastitis.

What is Mastitis and How Does it Affect Milk?

Mastitis is an inflammatory infection of a cow's mammary gland or udder, typically caused by bacteria entering through the teat canal. It is a painful condition for the animal and a major concern for the dairy industry due to its impact on milk quality and farm economics.

Key signs of mastitis include:

Udder inflammation: The affected quarter of the udder becomes swollen, warm, and painful.
Changes in milk appearance: Milk from an infected quarter can appear watery, or contain flakes, clots, or pus.
Blood in milk: In more severe cases, damaged capillaries in the udder can cause blood to leak into the milk, a condition called haemolactia, which can give the milk a pinkish, reddish, or brownish tint.

Dairy Industry Safeguards: How Retail Milk is Protected

For consumers, it is crucial to understand that the milk sold in grocery stores does not contain these contaminants. The dairy industry operates under strict food safety regulations and quality control measures to ensure the product is safe and wholesome.

Here are the steps that prevent contaminated milk from reaching the public:

Pre-milking Inspection: Dairy farmers are trained to visually inspect their cows for signs of mastitis before every milking session. Any cow showing symptoms is milked separately, and her milk is discarded.
Somatic Cell Count (SCC) Monitoring: All milk tankers are tested for their Somatic Cell Count, which measures the concentration of body cells, primarily white blood cells, in the milk. While healthy milk contains a normal level of white blood cells, a high SCC is a clear indicator of mastitis in the herd. Regulatory limits on SCC ensure that any milk batch exceeding the threshold is rejected.
Milk Pasteurization: The milk you buy is pasteurized—heated to kill harmful bacteria. While this process does not remove blood or pus, it would destroy any lingering pathogens.
Tanker Testing: Before a tanker of milk is unloaded at a processing plant, it is tested for quality indicators, including potential contaminants. A single contaminated batch from one farm can cause an entire tanker load to be rejected.

Understanding the Causes of Contamination

Mastitis is a complex issue, and its causes can be environmental, bacterial, or related to animal management practices. The diligent efforts of farmers and veterinarians are essential to managing this condition.

Causes of Blood in Milk

Mastitis: Inflammation from infection can damage the capillaries in the udder, leading to blood leakage.
Trauma: Physical injury to the udder or teats can rupture small blood vessels and cause bleeding.
Post-Calving: Freshly calved cows may sometimes have minor bleeding due to increased blood flow to the udder.

Causes of Mucus in Milk

Mastitis: The presence of mucus or thick, stringy milk is a common symptom of clinical mastitis, indicating an immune response to infection.
Other Udder Infections: While mastitis is the most common cause, other bacterial infections of the udder can also cause changes in milk consistency.

Prevention and Management of Mastitis

Prevention is the most effective approach to managing udder health and milk quality. Dairy farmers employ a variety of best practices to minimize the incidence of mastitis and ensure animal welfare.

Strategies to prevent mastitis include:

Maintaining Hygiene: Keeping milking equipment and cow bedding clean and dry is paramount to preventing bacterial infections.
Proper Milking Procedures: Using pre-milking and post-milking teat dips, and ensuring correct milking machine function, reduces the risk of infection.
Nutritional Management: Providing a balanced diet supports the cow's immune system, making it more resilient to infection.
Early Detection: Techniques like fore-stripping (checking the first few squirts of milk for abnormalities) and regular SCC testing help catch subclinical mastitis before it becomes severe.

Comparison of Normal vs. Mastitic Milk


Feature	Normal Milk	Mastitic Milk (Clinical)
Appearance	Uniform, white liquid	Watery, with flakes, clots, or stringy mucus
Color	White or slightly off-white	Can be pink, reddish, or brownish due to blood
Somatic Cell Count	Low (indicates healthy udder)	High (indicates inflammation/infection)
Consistency	Smooth and consistent	Thick, lumpy, or gelatinous
Taste/Smell	Neutral, clean taste	Can have an off, salty, or foul taste/smell
pH Level	Slightly acidic (around 6.6)	Elevated due to inflammation (alkaline, above 6.8)

Conclusion

The presence of blood and mucus in a cow's milk is an indicator of an underlying health problem, most commonly mastitis. However, modern dairy farming practices and stringent quality control protocols ensure that such contaminated milk is diverted and discarded, never making it to your glass. While raw milk from an infected cow is unsafe for consumption, the pasteurized dairy products available in stores are safe and healthy, backed by rigorous testing and sanitation standards. For those with continued concerns, understanding the robust measures in place can provide reassurance about the quality of the milk supply. Learn more about mastitis prevention from the Merck Veterinary Manual.

Frequently Asked Questions

No, store-bought milk does not contain blood or mucus. It undergoes rigorous quality control and testing that prevents milk from sick cows, particularly those with mastitis, from entering the commercial supply chain.

The most common reason for blood or mucus in a cow's milk is mastitis, an inflammatory bacterial infection of the udder. Trauma to the udder can also cause blood to appear.

Somatic Cell Count (SCC) is a measure of the white blood cells in milk. While a low level is normal, a high SCC indicates an inflammatory response to infection, like mastitis. Dairy industry standards set limits on SCC, and tankers exceeding this count are rejected.

Raw milk containing blood or mucus from an infected cow could contain harmful bacteria. However, this is not a concern for pasteurized milk. The infection is in the cow, and commercial milk is tested and treated to be safe.

Farmers prevent mastitis through strict hygiene protocols, proper milking techniques, and maintaining clean, dry bedding for their cows. They also perform regular health checks and monitor milk quality.

Milk safety is ensured through a multi-step process including herd health management, pre-milking inspections, bulk tank testing for SCC, and pasteurization. Any milk from a sick cow is discarded at the farm.

No, milk is not filtered blood. While milk is produced using nutrients from the cow's bloodstream, the milk components are manufactured by specialized cells in the mammary glands, not simply filtered from the blood itself.