PROTEIN-LEVELS IN BEEF-CATTLE FINISHING DIETS - INDUSTRY APPLICATION,UNIVERSITY-RESEARCH, AND SYSTEMS RESULTS

Consulting nutritionists were surveyed to determine current formulatio n and management practices for finishing beef cattle. Among the six co nsultants surveyed, percentage of CP in finishing diets ranged from 12 .5 to 14.4%, with urea levels ranging from .5 to 1.5% of DM. Finishing diets were based primarily on highly processed, rapidly fermented gra ins (steam-flaked and high-moisture grain), with roughage levels rangi ng from 3 to 11% of DM. All six consultants considered feed bunk manag ement to be a critical factor affecting feed intake and performance; f ive of the six consultants used aggressive implant programs based on e strogen + trenbolone acetate. Recent university research was reviewed with respect to CP level and source in finishing diets. Finishing catt le managed on aggressive implant programs seem to respond to higher le vels of CP better than would be expected fi om the factorial calculati on approach. Moreover, improvements in performance noted in recent res earch seemed to be more consistent when supplemental CP was derived fr om ruminally degraded vs undegraded sources. Calculation of protein re quirements with a metabolizable protein (MP) system yield estimates of protein needs by finishing cattle that agreed more closely with curre nt industry practices than did calculation based on the factorial meth od. The difference between the MP system and the factorial method was primarily a result of accounting for microbial N needs in the MP syste m. Reasons for production responses to CP levels that are greater than those calculated by the factorial method include increased accretion of protein by rapidly growing, implanted cattle, particularly during t he initial phase of the finishing period, alleviation of a microbial N deficiency, and ruminal and systemic effects of ruminally degraded N on acid-base balance of beef cattle fed rapidly fermented, high-grain diets. Reasons for production responses to supplemental CP need furthe r research.