Yet rumen microorganisms cannot tolerate high levels of fat. The types and levels of fats used in dairy cattle rations should be scrutinized closely both nutritionally and economically. Their concentration declines with the age of the plant and will vary with the proportion of leaves to stems. Some of the specialty products labeled as rumen inert are comprised of either triglycerides, free-fatty acids, or calcium salts of fatty acids. Fatty acids can be either saturated or unsaturated.
Unsaturated fats are more likely to interfere with ruminal fermentation than saturated fatty acids.
The fatty acids in whole cottonseed and full-fat soybeans contain large amounts of unsaturated fatty acids. However, whole oilseeds are less likely to interfere with ruminal fermentation compared to free oils. Whole oilseeds are slowly digested, allowing for a slow release of the oil in the rumen and more extensive microbial hydrogenation. Tallow is the most commonly fed animal fat. It is comprised of about 50 percent saturated fatty acids.