Diagnostic value of milk fat

It is very important to monitor and observe the trends of fat variation in milk and the relationship with other components. The ratio of milk fats to proteins can be a sufficiently reliable indicator in the diagnosis of acidosis or ketosis.

Determination of subclinical ketosis

As the ratio of milk fats to proteins approaches the threshold of 1.5, we can suspect subclinical ketosis in cattle. In such a case, the changes are associated with an energy deficit in the body due to the physiological state of cattle (e.g. after calving) or an improperly balanced diet.

The amount of fat is not constant during milking either. At the beginning of milking, the amount of fat in milk is about 1 percent, rising to 8 or even 12 percent in the last spurts of milk. Therefore, constant monitoring of milk fat can be important not only in the assessment of the health status of the animal, but also as an indicator of the proper performance of the milking process.

Fat-protein ratio in suspected ketosis
>1,4 There is a high probability that a cow has subclinical ketosis, the risk of clinical ketosis increases
1,3-1,4  Increased risk of subclinical ketosis
1,2 Optimal ratio of fats and proteins

Determination of subacute acidosis (SARA)

Fat-protein ratio in suspicion of acidosis
1,2 Optimal ratio of fats and proteins
1,0-1,1 Increased risk of subacute acidosis (SARA)
<1,0 The cow is more likely to have subacute ruminal acidosis (SARA), the risk of clinical acidosis is increased

The optimal ratio of milk fat to protein in the milk of dairy cattle should be ~1.2. When it reaches the limit of <1.0, it can be said that cattle have subacute acidosis. In such a case, the cause of the disease should be identified and eliminated as soon as possible. This can happen due to an excessive amount of grain in the diet or an excessive amount of concentrated feed given during a single feeding. Insufficient digestible fibre feed chopped too finely or feed raw materials contaminated with mycotoxins can also cause acidosis.

Methods for determination of fat in milk

It is very important to understand and monitor the trends in fat in milk and the relationship with other components (e.g. protein, lactose). To date, fat is usually determined by sending control milk samples to the laboratory, but with the development of technology, it is possible to integrate sensors in milk lines that would continuously measure the amount of fat in milk.

Röse-Gottlieb method

Reference study for determination of fat content in milk. The essence is the separation of fat from the test sample by treating it with concentrated sulfuric acid, isoamyl alcohol and centrifugal force. The method is reliable and accurate, but can only be performed in laboratories, as qualified personnel must use special equipment and reagents.  Also, this test takes a relatively long time, so it impractical for use in milk processing plants or farms.

Laboratory spectroscopic tests

Fats are more accurately determined by infrared analysis of their absorption and emission spectra. This methodology is very popular all over the world and is used in many laboratories to analyse the constituents of milk. Most often, such equipment is adapted for laboratory use, is quite expensive and requires qualified specialists. However, with the development of technology, there are opportunities to make this type of methods more practical and adapted for use not only in laboratories, but also on farms.

BROLIS HerdLine milk analyzer

The in-line milk analyzer BROLIS HerdLine is like a small laboratory on your dairy farm. The analyzer examines the composition of each cow’s milk during each milking. This “mini-spectroscope” is installed in the milking stalls or milking robot in the milk line and does not require additional reagents and special maintenance.

The analysis of fat, protein and lactose provides a proper evaluation of the health, productivity and economic efficiency of dairy cattle. The data collected during milking is processed in real time and can be viewed using the BROLIS HerdLine application.

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What affects milk fat?

Milk fat is one of the most valuable and variable components of milk. They consist of saturated (~60%) and unsaturated (~40%) fatty acids. More than 400 of them have been identified, but the main part of fat (~90%) consists of 15-20 different fatty acids. It also contains vitamins A, D, E, K.
The proportion and composition of fat may vary depending on the time of year and the composition of the feed. They are influenced by many factors in milk: genetics, lactation period, feed quality, environmental conditions, milking process, animal health status, etc.

Cattle breed

Cattle breed has the greatest influence on milk fat content. Some breeds of cattle (e.g. Jersey) produce fatter milk, while others (e.g. Holstein) produce milk with less fat. The milk of high-yielding dairy cows is usually leaner, while the milk of slightly lower-yielding dairy cows is fattier. Therefore, during selection, it is very important to pay attention not only to the quantity of milk produced, but also to its quality. Cows that give the most milk are not always the most economically beneficial.


The influence of feeding on milk quality is also very significant. It can be direct and indirect. In the first case, the digested fodder is absorbed as a source of milk production and energy, in the second – the microflora of the rumen breaks down the fodder into components and the initial elements for milk production are formed.

It is easy to increase fat content by feeding high-fibre forage such as hay, but this reduces the overall energy supply of the body and reduces milk production. A higher amount of starch in the feed increases the fat concentration in the milk, but it is essential to ensure the right balance between the protein and carbohydrates in the feed. Various feed additives (enzymes, probiotics, etc.) that can increase the amount of fat in milk are additionally included in the rations. Young grass is watery and has less fibre, so it is necessary to pay attention to this if the cattle are driven to grazing areas in the spring. A sudden change of feed usually disrupts rumen activity, so cows may start to have diarrhoea, while milk yield and concentrations of milk components decrease. Cattle should be introduced to ration changes gradually, adding new raw materials in small amounts during the transition period.

Physiological condition

The fat content of milk also varies during different periods of lactation. Most fat is found in colostrum. As the milk yield increases, the fat content usually decreases for the first 2 months and then gradually starts to increase again.

When a cow is in the estrous cycle, its milk and fat decreases. During the cycle of estrus, the amount of milk and changes in its components depend on the activity of the estrus and the characteristics of the cow itself.

In cattle suffering from mastitis, ketosis, acidosis or other diseases due to impaired digestion, the composition of fat changes, unsaturated fatty acids increase, lipidosis develops, and the quality of milk products deteriorates.

Environmental conditions

The amount of milk, as well as fat, is reduced by poor housing conditions (noise, rough treatment of cattle, etc.), poor milking practices due to unqualified personnel, untidy equipment, and ant sanitary conditions.