334 Evaluation of sources of RUP fed to Holstein steers in a simulated organic beef production system

Abstract

Abstract This study evaluated rumen undegradable protein (RUP) sources on performance of lightweight Holstein steers fed diets that simulated the requirements for organic beef production. Holstein steers (n = 59; initial BW = 213kg) were fed individually for 214 d. Diets contained 30% alfalfa haylage, 5% supplement to meet mineral requirements, and differing proportions of dry rolled corn and a protein source to supply RUP. Steers were assigned randomly to dietary treatments: a protein-deficient control (CON), field peas (FP), field peas and fish meal (FPFM), soybean meal (SBM), and a soybean meal treated to increase RUP (Soypass; SP). Diets were reformulated by phase as MP requirements decreased. Experimental design was completely randomized with experimental unit being steer. A tendency (P = 0.09) for a difference in ADG in the first phase was observed, with steers fed any RUP source having greater ADG than CON. No difference (P ≥ 0.22) was detected for ADG in subsequent phases as RUP sources were displaced with corn. Intakes were not different (P ≥ 0.26) among treatments during the first and last phase, but during phase two and three calves fed SP had greater DMI (P ≤ 0.03) compared with FP or FPFM, with the CON and SBM groups being intermediate. In the first phase, calves in the CON group had significantly (P < 0.01) lower G:F compared to treatments with RUP, which were not different from one another. No differences (P ≥ 0.31) were observed between treatments for G:F during the final three phases. These data suggest that supplementing RUP improved ADG and G:F, but source of RUP did not impact performance of lightweight Holstein steers when inclusions were varied to account for differences in RUP content of each protein source. These animals compensated for a deficiency in MP early in the feeding period.