Fat is much higher in energy compared to grains. Research has shown that high levels of fat in the diet (in excess of 6-8% of the ration dry matter) lowers forage digestion. The hypothesis is that fat in high fat rations coats the forage in the rumen making the forage inaccessible to the microform. In addition, high fat rations may alter the rumen microform populations. This usually means that approximately .4 lb to .6 lb of supplemental fat could be fed in a feeding program in high roughage diets. Supplementing 2 lbs of a 20% fat supplement would be an example of a supplementation program strategy when considering that there will be some fat coming from other feed sources in the diet. When developing beef cow diets, I keep the level of fat in the diet so not to exceed 5% fat in the total diet.

So to unravel the “fat” supplementation story for beef cows prepartum, it is unclear to me at this point if the source of fatty acids in the fat is important when supplementing beef cows in regard to reproductive performance. Questions arise as to what effect fat and the fatty acids may have on the cows’ metabolism and hormonal patterns. Fat is much higher in energy (TDN = 180%) than grains such as corn or barley; however, it appears that fat supplementation to cows is more than a direct energy response. I think it is safe to say that supplementing fat pre-calving will increase the brown adipose tissue in new-born calves and help them with the ability to tolerate cold stress. Until research help us define the specifics, it boils down to dollars and cents. If supplements that contain fat are economical, then use them in diet. For example, in the early Fall of 2006, whole soybeans were a great buy, and feeding them to mature cows at 2.5 to 3.5 lb/hd/day in some forage diets made for a very economical diet. In some location in the United States, distillers grains are a good buy and are used as an ingredient in some pellets and cubes. Distillers grains are about 12% fat and would be an excellent source of fat if priced to fit your program.