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Fat and protein content in milk. What farmers need to know.

Regular analyzes of fat, protein and urea content in milk provide rich information on the quality of cow nutrition and the possibility of improving these parameters in the long term.

The quality of milk is affected by many factors, but the most important are the feeding and husbandry of the dairy cows.

Errors in nutrition can cause many health problems for animals (acidosis, ketosis, disorders in mineral metabolism and others). As milk production increases, so does the risk of metabolic disorders. Of course, this does not mean that high-producing cows will get sick more often than low-producing animals. High milk yield only means that feeding must be based on accurate calculation of rations, perfect feed management and monitoring and analysis of the most important performance data. The fat and protein content of milk, the urea content of milk and the amount of milk produced are the data that can and should be used to evaluate animal nutrition and detect errors.

Milk fat

The milk fat content characterizes whether the required ration structure has been achieved. Since acetic acid is responsible for the formation of milk fat mainly in the rumen and is synthesized from plant fibers, the appropriate content of hay, haylage and straw in the diet is responsible for the normal level of milk fat (control of the ratio between bulk and concentrated forage and the amount of feed consumed). During the first weeks of lactation, the fat content indicates whether the animal is getting enough energy. Normally, the fat content decreases very sharply from the first to the fourth week of lactation, and then decreases a little more until the tenth week. After that, the fat content begins to gradually increase and this continues until the beginning of lactation, which indicates that the animal begins to replenish its fat reserves.

A high fat content (usually more than 5%) during the first 2 - 4 weeks after calving indicates intensive mobilization of fat from the cow's body. Often these animals have a low milk protein content (less than 3.1%) at the same time. This is a signal of possible ketosis of the animal. This usually affects older animals with a very intensive metabolism. But animals that have been overfed during the previous lactation and during the dry period can also react in this way. Normally, the milk yield of such cows increases very sharply during the first weeks of lactation, but they eat little feed. Such ketosis reaches its peak between weeks 3 and 5 of lactation.  

A low fat content may be a suspicion of acidosis, usually due to an inappropriate ration structure (in the first weeks of lactation, it is often due to too rapid an increase in concentrate intake or insufficient feed intake in general). Significant fat gain in individual animals of more than 0.4% between two control milkings and a fat/protein ratio below 1.0 may be evidence of acidosis.

A barn temperature above 27ᵒC, combined with high humidity, can lead to a reduction in fat content by 0.2 to 0.5 % (for the whole herd). Health problems (liver disease, parasites, diarrhea, hoof disease, hormonal disorders) can also reduce fat content.

Milk protein is an important indicator of milk quality and modern genetics is aimed at increasing it. The task of the producers is to develop the full potential of the animals, including the high protein in the milk.

The protein content of the milk reflects whether the cow is well supplied with energy and is a kind of energy barometer for the herd. The protein content of milk depends on whether the microbes in the rumen that synthesize microbial protein have sufficient energy available. Only with high productivity does the protein in the rumen, which does not break down, become more and more important.

The protein content of milk during the first two months of lactation varies according to the body condition of the animal. Normally, during the first third of lactation, milk protein decreases with increasing milk yield, as energy is in short supply during this period. Protein above 3.1% is considered normal during this period. But if it falls below 2.8%, it means that the animal no longer has energy reserves in the body. In any case, even a very high milk yield of over 50 kg per day, the protein content of the milk should not fall below 3.1%.

As the animal begins to gain weight again and its condition score increases, milk proteins also increase and milk yield decreases. At the end of lactation, milk protein values up to 3.8% are considered normal. Protein values above 3.8% signal a significant reduction in productivity. This development is closely related to the accumulation of fat. In late lactation, milk production is almost independent of body condition if it is between 3.0 and 3.5. At a higher body condition, above a score of 3.5, we must prepare for a very sharp drop in productivity in combination with a very high protein value (above 3.8%). 

Urea in milk

Urea in milk is an indicator of rumen supply of microbial nitrogen based on crude protein. The content of urea below 15 mg / 100 ml of milk indicates a noticeable nitrogen deficiency in the rumen. This limits the activity of microorganisms in the rumen, which leads to reduced feed intake and, accordingly, to lower milk production.

The optimal content of urea in milk is about 25 mg / 100 ml. Urea above 30 - 35 mg / 100 ml indicates an excess of nitrogen and crude protein in the rumen. In this case, the nitrogen metabolism is overloaded.

The amount of urea in milk reflects the value of the nitrogen balance in the rumen (RNB, BAR) from 0 to 10 g corresponds to a urea content of 20 - 25 mg / 100 ml.

Fats and proteins in milk must be in a certain ratio with each other. A ratio of 1.1 : 1 to 1.5 : 1 indicates a balanced diet.

A fat-to-protein ratio greater than 1.5, especially in early lactation (except during the lactation period), is a warning signal. A high fat content is a sign of very strong fat mobilization by the body. low protein content indicates a lack of energy, although some of the energy comes from the body's reserves. This can lead to metabolic disorders (ketosis).

If the fat/protein ratio is more than 1.5 throughout the lactation period, this indicates a diet rich in structure but poor in energy. Especially if the quality of the bulk feed is poor and the concentrates are insufficient. This results in low milk production and low milk protein content.

A very low fat-to-protein ratio (below 1.1) occurs with a diet rich in energy and poor in structure (many concentrates). In this case, it is necessary to distribute the feed correctly depending on the productivity.

When interpreting the ratio of fat / protein in the first third of lactation, it should be taken into account that both the threat of ketosis (at a high indicator) and the threat of acidosis (at a low indicator) are possible. In this case, the "normal" ratio of fat / protein may turn out to be incorrect. Careful monitoring of animals during this period is therefore necessary, and perhaps even individual data collection and analysis of animals up to day 30 of lactation.

To detect feeding errors during the year, the fat and protein values of the collected milk can be analyzed monthly. For example, if fat and protein values decrease at the beginning of May, this may mean that the transition to grazing was not sufficiently structured or was carried out too abruptly.

Control milking data provides valuable information for monitoring animal nutrition and should be actively used by every farm.

Amount of milk

The genetic potential of the dairy cow can only be realized if it is well fed. the productivity of the healthy cow is relatively high during the first two to three weeks of lactation, even when there is a shortage of nutrients. With good nutrition, the decline in productivity is gradual. Conversely, with improper feeding, milk yield sharply decreases. Therefore, the tracking of the lactation curve allows to monitor the feeding.

Regardless of the lactation curve, changes in productivity are influenced by forage quality and digestibility. And fluctuations in milk yield are always affected by a sudden change of forage (change of meadow, new grass silage, etc.).

Carbohydrates in milk

The main carbohydrate in milk is lactose. This disaccharide has a faint sweet taste. The concentration of lactose in milk remains relatively constant - on average about 5% (4.8 - 5.2%). Unlike the fat concentration of milk, the lactose content is approximately the same in all dairy breeds and is not easily altered by dietary factors.


Feeding errors can immediately lead to an imbalance in the biological balance in the cow's body. The use of data on the quality and quantity of milk makes it possible to promptly recognize and eliminate such violations. Regular analysis of fat and protein in milk is a valuable diagnostic aid in monitoring animal health and should be actively used by every dairy. 

Invaluable in this respect are the ultrasonic milk analyzers of the company Milkotester Ltd. Lactomat and Master, which with extreme precision determine not only the content of milk fat and proteins, but also dry fat-free residue, density, lactose, salts, added water, freezing point , sample temperature. Their use enables specialists and farmers to monitor the content of the main milk ingredients on a daily basis and to adjust the food ration in a timely manner.

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