High-Shear Dry Extruded Soy Meals Fed to Dairy: What Happens to Milk Fat?
In dairy production, the total amount of milk produced each day per cow is important, but it’s really the components, milk fat and protein, that are the most valuable per unit produced. A common goal for dairy nutritionists is to formulate a dairy ration that will maximize the amount of milk fat produced each day.
Often, by-pass soy ingredients are used to add more rumen by-pass protein to the diet in order to boost production. Many of these contain residual oil, and along with other ingredients that contain fat (including isolated fats and oils), the total amount of fat in the diet is calculated and controlled.
It’s important to understand how added fats and oils, including those that come along with by-pass soy ingredients, affect milk fat production in dairy cows.
I took data from carefully-controlled studies (see here, here, and Dhiman, 2001) that fed high-shear dry extruded full-fat soy and ExPress® (dry extruded/pressed for partial oil removal) soy meals in dairy rations in order to determine how their usage:
- Added fat to the diet
- Affected milk fat percentage
- Affected total amount of milk fat produced each day
The data summary is shown below:
Figure 1. More fat in the diet from high-shear dry extruded soy meals only minimally affected milk fat daily yield.
As shown in Figure 1, adding high-shear dry extruded soy meals to dairy rations, in typical-to-high levels, had only minimal, if any, effects on milk fat production. In these studies, milk fat percentages ranged from 2.91 to 3.42%.
It’s also important to consider what happens to milk fat when the total levels of dietary fat, including contributions from extruded soy meals, are increased. What happens when the total dietary level of fat is increased?
Figure 2. Increasing total fat in the diet beyond about 1.5 kg/cow/day reduces milk fat daily yield.
As the data in Figure 2 indicates, increasing total dietary levels of fat will indeed begin to reduce milk fat production.
So, as the data from these 3 carefully-controlled studies indicate, high-shear dry extruded soy meals can be used very successfully in dairy diets. Also, total dietary fat levels must be controlled in order to avoid milk fat suppression.
Dhiman, T.R., 2001. Influence of soybean meal processing techniques on yield response of cows. Utah State University Research Report.