Applying effective energy concept for intake prediction and balancing ruminal nitrogen and post-ruminal amino acid requirments for beef cattle

Proper animal nutrition involves balancing nutrient supply to nutrient requirement. Accurate intake prediction is fundamental to diet formulation and appears simple but has historically been challenging to accomplish. Multiple factors control intake and understanding process of intake control is complicated by a plethora of interactions among these factors. Several intake prediction equations have been developed and equation accuracy has been improved by applying various adjustment factors. Research has been conducted that allows requirements of ruminal degradable peptide and nitrogen and absorbable amino acids required for growth to be estimated. However, requirement of these compounds is based upon caloric-supported growth, or accurate intake prediction. The first experiment in this dissertation examined the validity of effective energy intake predicting equations. Accuracy of effective energy equations (EE) was compared with NRC equations based on initial body weight (NRCiBW) and dietary NEm concentrations with (NRCNEm-mon) and without monensin adjustment (NRCNEm), and net energy equations (NE) based on net energy requirements for maintenance and gain. The EE equations more accurately predicted intake, had less variation and the greatest coefficient of determination (r2), and smaller line bias decomposition. These findings support the conclusion that EE models were the best for predicting intake by steers. The second study implemented EE intake prediction in a diet formulation model to formulate diets with inadequate, balanced or sufficient ruminal degradable nitrogen to support microbial growth requirement in vitro and in vivo. In an in vitro continuous culture study, there was a cubic response (P < 0.01) for grams of bacterial nitrogen produced by rumen microbes and MOEFF when RDN was increased. The MOEFF was maximized when RDN requirement and supply was balanced. In an in vivo animal growth study, greater (P < 0.01) feed efficiency was found in negative RDN balance diet (-0.69% RDN balance diet), which was presumably due to recycled nitrogen supply meeting the estimated deficiency. Finally, research was done to determine the effect of post-ruminal arginine levels on animal growth and how balanced/unbalanced RDN and post-ruminal arginine diets with and without roughage would impact animal growth performance and feed efficiency. We hypothesized that there would be no further improvement in feed efficiency once RDN and post-ruminal amino acid requirements were met. Two animal growth experiments were conducted. No significant difference in ADG, but DMI and feed to gain ratio were greater (P < 0.01) when RDN and postruminal arginine requirement were met. In the second animal trial, post-ruminal arginine levels resulted in no difference in ADG during 168 days on feed; however, the balanced post-ruminal arginine diet was observed to have greater period ADG (0--28 days and 0--87 days ADG, P ≤ 0.08) and lower feed to gain ratio (more efficiency). In summary, the effective energy equation is a better estimation for intake and beneficial to improve MOEFF and feed efficiency by formulating diet to meet ruminal degradable protein, ruminal degradable nitrogen and absorbable amino acids requirements, respectively. The implication of these experiments is feed efficiency could be maximized by formulating diet to meet ruminal nitrogen required for microbes and post-ruminal amino acid requirement. Accurate animal gain potential estimates and dietary energy densities would improve intake prediction accuracy and post-ruminal amino acids flow assessment.