Using Rumen Undegraded Protein in Beef Diets to Improve Growth Performance in the Feedlot

A major determinant of production cost in the feedlot is the feed conversion ratio (FCR). The primary factors influencing FCR are digestible energy (DE) content of the diet and absorbable amino acid to metabolizable energy (AAME) ratio. Great improvement in DE would occur by removing roughage from the diet. Improving AAME in the diet requires accuracy in predicting absorbable amino acid flow from the rumen.

Roughage is included in high concentrate diets to alter fermentation, with the main objective to regulate acid production and pH influence. In most beef feedlot diets, rumen degradable protein (RDP) is fed in excess of that required by ruminal microflora. It is possible to calculate the RDP required (both peptide and ammonia nitrogen) by the ruminal fermentation to maximize microbial efficiency. This in turn allows the amount of RDP needed in the diet to be determined. When excessive RDP is fed in the diet, the rapidity of fermentation is increased and therefore the production rate of organic acids. This in turn we believe increases the acid load in the rumen and the millliequivalents of acid absorbed by the animal. When the RDP is matched to microbial protein synthesized from the carbohydrate mass fermented in the rumen, the production of organic acid is not as rapid and curtails ruminal pH drop compared to feeding excessive RDP. This is why we believe roughage can be removed from the diet without ill consequences on rumen health or animal performance. Removing roughage from the diet, the most indigestible dietary component in a high concentrate diet, substantially improves the digestible energy density of the diet, resulting in improved FCR and reduced manure volume.

The absorbable amino acid flow from the rumen is the combination of RUP and microbial protein. The RUP protein in feedstuffs is measurable. What has been elusive is predicting microbial protein flow from the rumen. We derived quadratic equations that have been acceptably accurate in predicting microbial protein (amino acid) flow from the rumen. The derivation of these equations has made it possible to predict the amino acid flow from the rumen, compare flow to amino acid requirements of the animal, and then identify the level of RUP needed to optimize the AAME in the diet.