Increasing the proportion of grain in the diet is limited because dairy cows require a minimum amount of fiber and forage in the diet for proper chewing and rumination, and to maintain normal fat test. This energy deficit has created an interest in the use of animal, vegetable and ruminally inert fat sources to increase the energy density of diets for high producing cows. A Pennsylvania field study found first-service pregnancy rates of 62 percent for cows fed 1 pound of ruminally inert fat per day during the first 150 days of lactation, versus 42 percent for cows that weren't fed fat. Dairy managers who supplement fat have noticed improved body condition and persistency of lactation, and possibly improved reproductive performance in herds where under-conditioning was severe. Protein feeding Researchers are now investigating the effects of protein feeding, and some have found that high levels of dietary crude protein can impair reproductive performance.
More research is needed, however.
A portion of the crude protein in feeds is degraded by rumen microbes to peptides, amino acids, and ammonia with the remainder escaping microbial breakdown. If adequate fermentable carbohydrate is present in the rumen, degraded intake protein and NPN can be incorporated into microbial protein and sent, along with undegraded intake protein, to the small intestine for digestion and absorption. More research is needed to define the role of BUN as a diagnostic tool. From a practical standpoint, it does not make economic sense to overfeed or underfeed protein to lactating dairy cows. Minerals and vitamins Table 4 presents the NRC recommendations for minerals and vitamins for high producing cows.