Your cows need it. But what type of fat – and how much – should your herd’s rations include?
By Dr. Essi Evans, Essi Evans Technical Advisory Services, Inc.
Fat is a key source of storage for energy since tissues use stored fat when cows are in negative energy balance. Cows have the ability to synthesize fat for tissue storage and milk fat, but it is more efficient to use fat obtained from the diet for these purposes.
The big questions to answer when formulating diets are: What type of fat and how much of these fat sources should rations include?
How Much Fat?
A rule of thumb is to formulate rations with adequate levels of fat in the diet to roughly equal the amount of fat cows produce in milk.
Therefore, if a group of cows produces 100 pounds of milk with a 3.5% fat test, daily intake should not be more than 3.5 pounds of dietary fat in the ration.
What Kind of Fat?
The question of what kind of fat to include in rations is a bit more difficult to answer.
Fat is made up of fatty acids, much in the same way proteins are made up of amino acids. Fatty acids can be:
• Saturated (usually limited to tallow in dairy diets)
How Do Fats Work?
Saturated fats do not have a significant impact on rumen fermentation, and pass through the rumen into the small intestine for digestion. However, saturated fats are not digested as well as unsaturated fats.
In general, rumen microbes try to saturate the mono- and polyunsaturated fatty acids. High dietary levels of unsaturated fatty acids can disrupt rumen fermentation leading to a reduction in the amount of valuable microbial protein that is produced.