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It has long been known that adequate energy is required for high reproduction in beef cows. Historically, most high energy supplements contained starch from grains such as corn, barley, etc., which may cause some negative effects on forage digestion when fed at relatively high levels. This is especially true when the ration is deficient in protein. An alternative to energy supplementation is utilizing plant and animal fat, which are much higher in energy than grains such as corn or barley. Early research has shown that very high levels of fat in the diet (in excess of 6-8% fat in the overall diet) lower forage digestion. It is felt that this may be due to fat coating the forages and may also alter the rumen microflora populations.
On the positive side of fat supplementation, more recent research was released from Ft. Keough (USDA) Station at Miles City, Montana that showed when 2 year old heifers were fed crushed safflower seeds, which are high in fat, before calving that pregnancy rate increased 18.5%. This research was initiated to evaluate the effect of fat supplementation on cold tolerance of new born calves, which was why the fat supplement was only fed pre-calving. Fat did appear to improve the cold tolerance of the new born calves, which is believed to be due to an increased level of "brown fat" in the new born calf, which is readily available as an energy source of the new born. In this early study the crushed safflower seeds that were fed were high in linoleic acid, which may be important in the composition of deposited fat. Although a tremendous gain was made in reproduction, a concern with this data is that the controls that were not fed supplemental fat only had a 57% pregnancy rate. This of course is usually much lower than experienced in most cow herds even with 2 year old, first calf heifers.