Analysis of milk fatty acids: a rapid diagnostic system for business management
D. M. Barbano et alii
Milk fat is composed by fatty acids (FA) which, depending on the length and unsaturation of the chain, can be divided into 3 categories: de novo (from C4 to C15), of mixed origin (C16:0, C16:1, C17:0) and preformed (C18:0 and over). The nomenclature derives from their genesis: de novo FA are synthesized in the breast and are influenced by ruminal function, while mixed origin FA and preformed FA derive from diet and, in the second case, they are mobilized by body fat.
The introduction of med-infrared (MIR) for the rapid analysis of milk fatty acids (FA) let screen the FA in a simple and cheap way detecting the quantity for each fraction.
This data can be very useful in the perspective diagnostic system, since a study by the department of Food Science, of Cornell University, has highlighted a correlation between the variation of the FA profile of bulk milk and some aspects of feeding and herd management. For example, the stable that have a lower stocking density and a higher frequency of feeding distribution have a higher percentage of de novo fats, as well as diets with lower EE values. On the other hand, the characteristics of the diet such as dry matter, crude proteins, NDF, starch or forage percentage are not relevant on the fatty acid profile. So, overstocked stables, with reduced feeding frequency and a higher fat content in the diet have been associated with lower de novo FA synthesis.
For the same production of milk (Kg/ cow), the farms that have a high fraction of de novo FA also have higher percentage of EE and CP. The positive correlation between de novo FA and milk protein is due to the higher microbial biomass that provides essential amino acids to support milk protein synthesis in combination with the non-degradable rumen proteins.
In conclusion, when de novo FA> 0.85 g/ 100 g of milk and mixed origin FA> 1.35 g/ 100 g of milk, the rumen fermentation of carbohydrates works well and the supply of volatile fatty acids from rumen is good. This optimal situation is represented, in the figure below, in the second quadrant (top right), where the milk fat is good (>3.8%) and the de novo FA is > 0.8 g/ 100 g of milk. In a different scenario, the farmer could have a good EE value in the bulk tank, but a low de novo FA value (<0.8 g/ 100 g of milk), he should wonder about the management of the herd (overstocked stable or reduced feeding frequency), the excessive fat content in ration or problems of ruminal funcionality.
The positive correlation between the rise of de novo FA and the percentage of EE and CP in the bulk milk can be used as an index of the quality and the balance of the rumen fermentation and also as a tool for evaluating changes in the diet and in the herd management. Milk FA tests could represent a diagnostic approach for both the whole cattle and specific subgroups (DIM, age, diet, etc.).