Milk fat plays a big role in the economic and nutritional value of the milk. Hence, a decrease in milk fat concentration will seriously impact the farm's profitability. However, researchers have done a good job in outlining the factors that cause low milk fat.
Factors affecting milk fat:
Often times, milk fat depression is related to the diet fermentability as well as the polyunsaturated fat load.
One needs to determine the drop in milk fat is diet related or seasonal response before making any changes.
Generally, milk fat hits its peak after New Year and it reaches a low point in July.
Hence, farmers need to be careful and decide if they want to give up milk yield in exchange for higher fat percentage during summer time.
Another theory which became widely accepted to explain diet induced milk fat depression is the ruminal biohydrogenation theory.
It basically states that the rumen biohydrogenates (transforms) the fatty acids found in forages, fat products, oil, byproducts and so on to get rid of the double bonds and create a more saturated fatty acids.
Certain intermediate fatty acids will form during the biohydrogenation process and it is the cause of milk fat depression.
The amount of unsaturated fat substrate available to the rumen bugs will dictate how quickly the milk fat percentage drops.
Ways to improve milk fat
To fix the low milk fat percent, one needs to reduce the amount of biohydrogenation intermediates leaving the rumen.
One way is to slow the passage rate by adding fiber, however, that will decrease total milk volume.
Often times, fixing requires removing unsaturated fat or shifting the microbial community within the rumen.
Depending on how upset the microbial balance gets, it could take days or a couple of weeks to return to the desired profile.
Data is limited, but studies have shown that at cellular level, when the milk fat depression causing intermediates passes through the rumen, the enzymes in the mammary gland responsible for milk fat synthesis become downregulated.
Hence in order for the milk fat production to improve, these enzymes must be upregulated back to normal.
2 things need to be fixed: 1) the rumen microbial community 2) the cellular mechanisms in the mammary gland.
Studies have shown that it will take around 21 days for the milk fat percentage to return back to normal assuming the problematic risk factors are removed.
Therefore, producers must be patient once ration has been corrected and the fat dropping trend is reversed.
Here are some checklist to go through to help determine the root of the problem and start finding solutions:
TMR particle size
Particle size sorting of the TMR
Rate of fiber digestibility
Mixer wagon scale accuracy
Effective neutral detergent fiber (NDF) of the ration
High water sulfates
Amount of unsaturated fatty acid intake (should be under 700g a day per cow)