The cow is most efficient in energetic terms if fat makes up about 20 to 25 percent of the net energy consumed, although it may not be always practical to feed this amount. A useful guideline is to feed as much fat as the cow is putting into the milk tank. Thus, if she is producing 40 kgs per day, with 3.5 percent fat, then you should feed 1.5 kgs of fat in the total ration. When computing this amount, it is important to include the fatty acids that are components of the base ration. This amount usually is less than 3 percent of the feed dry matter with rations consisting of alfalfa and grass forages, and grain.
Barley contains half as much fatty acid as corn.
Fatty acid content of the total ration is about 1 percentage unit less than the ether extract value. The maximum that can be used depends on factors such as amount and quality of forage in the diet, frequency of feeding, use of buffers and so on.