Submitted to: Nutrition and Management Conference Proceedings
Publication Type: Review Article
Publication Acceptance Date: February 1, 2006
Publication Date: February 22, 2006
Citation: Cole, N.A. 2006. Update on recent protein research for finishing beef cattle fed steam flaked corn based diets. In: Proceedings of the 21st Annual Southwest Nutrition & Management Conference, February 23-24, 2006, Tempe, Arizona. p. 67-87. Technical Abstract: Seven cooperative experiments were conducted to determine the effects of dietary CP concentration and source on performance, carcass merit, site and extent of digestion, and potential ammonia emissions of finishing beef steers fed steam-flaked corn-based diets. In Experiments 1, 2, and 3, diets were arranged in a 3 x 3 factorial with three CP concentrations (11.5, 13, or 14.5% of DM) and three sources of supplemental CP (N basis): 100% urea (U); 50:50 blend of urea and cottonseed meal (B); or 100% cottonseed meal (C). Steers were initially implanted with Ralgro and reimplanted with Revalor-S on d 56. Two performance studies were conducted at Texas Tech and NMSU using 585 British x Continental steers (avg BW 728 lb; nine pens/treatment:Exp. 1). Digestion trials (Exp. 2) were conducted at TAES in Amarillo and Texas Tech using the same diets as Exp. 1. Dietary effects on potential ammonia losses were determined using feces and urine from the digestion trials in an in vitro (Exp. 3) and an in vivo (Exp. 4) system. A phase feeding trial was conducted at NMSU in which the CP concentration of the diets was decreased with 56 days left on feed (Exp. 5). The effects of oscillating dietary CP on performance and potential ammonia losses were determined in Exp 6. Ammonia emissions were measured using micrometeorology methods at a 50,000 head feedyard during 4 seasons in Exp. 7. In Exp. 1, CP concentration affected ADG (P < 0.05) quadratically. Increasing the dietary concentration of supplemental urea relative to cottonseed meal linearly increased ADG and G:F (P < 0.05). Dry matter intake was not affected (P > 0.10) by either CP concentration or source. Fecal N excretion was not affected by CP concentration but urinary N excretion increased with increasing dietary CP concentration and with days on feed in Exp. 2. Potential ammonia emissions increased with increasing dietary urea (Exp. 3) and CP concentration (Exp. 3 & 4). Ammonia losses were approximately 25% greater in steers fed 13% CP diet than in steers fed 11.5% CP diets. Ammonia losses increased exponentially with days on feed (Exp. 3). Phase feeding decreased potential ammonia losses by approximately 25% but adversely affected animal performance (Exp. 5). Oscillating dietary CP (10 vs 14% at 48 hr intervals) tended to improve steer performance (Exp. 6) and decrease ammonia losses compared to continuously feeding a 12% CP diet. Ammonia emissions from a feedyard during the summer were 2x greater than in the winter and the annual average was 33 lb/head or approximately 50% of N intake (Exp. 7).