Low-milk-fat syndrome, commonly known as milk fat depression (MFD), has been studied for approximately 170 years. Many hypotheses have been evaluated in order to explain the biological mechanisms by which nutrition could modulate milk fat percentage.
Today, the most accepted theory is the âbiohydrogenation theory,â which postulates that specific intermediates of unsaturated fatty acid biohydrogenation inhibit mammary gland lipogenic enzymes and consequently lead to decrease in milk fat synthesis.
Currently, several conjugated linoleic acid (CLA) and other intermediates, such as trans-C18:1 FA, have been associated with MFD. Most recent studies have demonstrated significant MFD with a relatively small amount of those intermediates of biohydrogenation reaching the mammary gland.
Another aspect of MFD is the determination of time of induction and recovery, knowing these times could assist dairy nutritionists to understand what may have caused MFD and how long they should wait until they observe an improvement in milk fat.
A study has demonstrated that feeding a low-fiber and high-oil diet decreased significantly milk fat synthesis in seven days, and the same cows took approximately 10 days to recover milk fat to a similar original value.
The amount and type of those intermediate unsaturated fatty acids of biohydrogenation in the rumen will depend on several factors, especially the amount of unsaturated fatty acids intake and rumen pH.
The main sources of unsaturated fatty acids (oil) are the grains in the silages (i.e., corn silages), supplements (corn grain, high-moisture corn, etc.) and in some co-products such as DDGS.
The second important factor that increases the risk of MFD is a lower rumen pH, which depends on amount and type of starch in the diet as well as the level of effective fiber supplied by forages.
A recent study showed that substituting 25 percent of concentrate by corn milling products in diets containing similar forage NDF (starch level was reduced from 33 to 27 percent) increased milk fat percentage and milk fat yield due to a higher rumen pH.
In the same study, the author tested the substitution of concentrate and forage at 25 or 40 percent; in this case, forage NDF and starch were reduced, which was associated with the observed MFD in both cases.
This interaction between the level of oil in the diet and rumen pH affected by level of forage, particle size of TMR, starch level and rumen degradability, sorting, etc., will determine the final risk level of MFD.
Thus, when considering the optimum inclusion of some co-products, such as DDGS, it will depend on the other factors of the diet and management of that specific farm.
Corn milling products such as DDGS can vary in their nutritional content, especially fat concentration, which in this case is mainly composed of unsaturated fat.
A study tested if short-term variation in the concentration of unsaturated fat would negatively affect milk production and its components. The authors tested high (range 2 percent) and moderate (range 1 percent) variations in fat for 16 days in cycles of four days.
Cows in the high-variation group had lower dry matter intake and milk yield at the end of the experiment. Interestingly, in the short term, the high variation did not have an effect on milk components, but in the long term it did. In addition, the concentration of trans-10, cis-12 CLA in milk was higher, suggesting an alteration in rumen microbial population.
The complexity of all variables surrounding MFD implies the need for more sophisticated formulation systems and lab analysis.
Thus, successful diet formulation that maximizes margin by the optimum inclusion of forages and co-products, whereas maximizing milk and milk component production, will be the consequence of the use of precise lab analysis.
The use of complex formulation models will also help understand nutrients for available ingredients, determine their variability and consider how these measurements (especially for unsaturated fatty acids and rumen pH) and their interactions with forage quality, mixing, sorting, overcrowding, etc., impact MFD. PD
References omitted due to space but are available upon request. Click here to email an editor.
Gustavo Cruz and Guillermo Schroeder
Cargill Animal Nutrition
