Effects of Balancing Feedlot Diets for Amino Acid Requirements and Effective Energy Using Rumen Protected Lysine on Growing Steer Performance.

The objective of this study was to evaluate differences in growth characteristics and feed efficiency of feedlot steers consuming varying levels of rumen protected lysine. We hypothesized that steers consuming a diet optimized for effective energy (EE) and containing rumen protected product meeting predicted lysine requirement would have greater feed efficiency and gain, and lesser intakes than steers consuming diets formulated below or above requirement. After a 3 wk adaptation period, crossbred steers (n = 120; 269 ± 23 kg) were stratified by BW and color, sorted into pens of six and fed for 75 d. Diets were balanced to meet effective energy (EE) requirements and not be limited by non-lysine amino acids. Treatments included a lysine-limiting control that contained no rumen protected products (NEGCON); a lysine-sufficient control that contained rumen protected soybean meal (POSCON); treatment that contained 50% of encapsulated lysine (Aji Pro 3G, Ajinomoto Heartland, Inc.) needed to meet predicted lysine requirement (AJ50); a treatment that contained 100% of encapsulated lysine needed to meet predicted lysine requirement (AJ100); and a treatment that contained 150% encapsulated lysine needed to meet predicted lysine requirement (AJ150). AJ50, AJ100 and AJ150 were predicted to provide 9.3, 18.6 and 37.3 g/hd/d Aji Pro 3G, respectively. Cattle were fed once daily and consumed feed ad libitum from GrowSafe feeders (GrowSafe Systems Ltd., Airdrie, Alberta, Canada), from which feed intake was measured daily. Data were analyzed using the PROC GLM procedure (SAS, v 9.4). Initial BW (kg) did not differ across treatments (P = 0.85). Final BW (kg; 396 ± 29) was significantly greater for AJ100 (408) than NEGCON (392; P = 0.05) and AJ50 (392, P = 0.05) and tended to be greater than POSCON (394, P = 0.10) and AJ150 (393, P = 0.08). Animal DMI (kg/d) did not differ across treatments (P = 0.57). However, DMI (%BW) was significantly lesser (P = 0.05) for AJ100 (1.50) than AJ150 (1.63). Differences in ADG (kg) were not observed between treatments (NEGCON = 1.68, POSCON = 1.65, AJ50 = 1.70, AJ100 = 1.84 and AJ150 = 1.70; P = 0.73.) No treatment differences in F:G (P = 0.61) were observed for AJ100 (4.32) versus NEGCON (5.15), POSCON (5.05), AJ50 (5.06) and AJ150 (5.13). When optimized for amino acid and EE requirement, AJ100 steers had statistically greater FBW and statistically lesser DMI (%BW) than steers consuming other treatments.