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Title:Determining rumen degradable protein requirements in growing beef cattle
Author(s):Klatt, Brady Joseph
Advisor(s):McCann , Joshua C
Contributor(s):Shike, Daniel W; Cecava, Mike
Department / Program:Animal Sciences
Discipline:Animal Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):beef cattle
rumen degradable protein
growing cattle
Abstract:Nutrition is an essential component of livestock production. Diets need to be formulated to optimize growth and performance,but providing nutrients with cost management in mind is also important. Specifically, supplying the correct amount of protein to livestock is critically important as it is usually the most expensive macronutrient. Accordingly, the objective of livestock nutrition models should be to describe individual nutrient requirements for an animal and potential ingredients that can be fed to obtain maximal production efficiency. Although the purpose of livestock production is to convert otherwise inedible carbohydrates and protein in animal feed to useable food sources for humans, only 5 to 30% of animal feed N meets this goal (Kohn et al., 2005). Protein contents of diets can easily be obtained by calculating crude protein (CP) values, and cattle have been fed using this system for decades. However, the downside of this methodology is that it fails to partition protein content of the diet into rumen degradable protein (RDP) and rumen undegradable protein (RUP). The segmentation of protein by rumen degradability is needed as microbial populations digest and alter feedstuffs before host utilization. Burroughs et al. (1974) proposed the metabolizable protein (MP) system which accounts for microbial protein supply as well as the RUP fraction delivered to the small intestine unaltered. This system is considered a more effective approach to ruminant protein supplementation. Yet, the increased complexity associated with accurately predicting microbial growth has limited its widespread use by consulting nutritionists (Samuelson et al. 2016). Recent adjustments were made to improve accuracies of the MP model in the National Academies of Science Engineering and Medicine (NASEM, 2016). Most significantly, reductions were made to RDP requirements for growing cattle fed silage-based growing diets. Two experiments were conducted to assess RDP requirements in the growing steers. In experiment 1, fall-born, early-weaned steers (N = 120) were fed 1 of 2 dietary treatments during an 85 d growing period. Treatments were formulated to provide RDP at NASEM (2016) requirements (REQ; CP=14.5%; RDP=7%) or exceed requirement (EXS; CP=17.5%; RDP=10%). Steers were weighed on d -1, 0, 1, 14, 28, 56, 84 and 85 and blood samples were collected on d 28 and 85 to assess blood urea N (BUN). Final BW, gain:feed and ADG were not affected (P ≥ 0.42) by treatment. Treatment affected (P < 0.01) BUN levels with EXS steers having greater BUN levels than REQ steers. In experiment 2, six Simmental × Angus steers (BW = 324 ± 22 kg) with ruminal and duodenal cannulas were used in a replicated 3 × 3 Latin square design. Periods were 18 d with 12 d for adaptation and 6 d for total collection of feces and urine. Ruminal pH, ruminal NH3, and BUN samples were determined on d 18. Steers were limit-fed (2.3% of BW) diets with varying inclusions of urea formulated to be deficient in RDP (Low-RDP; CP = 13.2%; RDP = 5.5%), meet RDP requirements (Req-RDP; CP = 15.2%; RDP = 7.5%), or exceed RDP requirements (Hi-RDP; CP = 17.5%; RDP = 9.8%). While DMI was not affected (P = 0.20) by treatment, N intake increased (P < 0.01) with greater dietary RDP. Fecal N was not different (P = 0.69) across treatments, but steers fed the Hi-RDP diet had the greatest (P < 0.01) urine N. Retained N did not differ (P = 0.36) between treatments, but Hi-RDP steers had decreased (P ≤ 0.02) retained N as a percent of N absorbed. Microbial N flow, microbial OM flow, and microbial efficiency did not differ (P ≥ 0.26). A treatment × hour interaction (P < 0.01) was observed for ruminal NH3 as steers fed Hi-RDP diets had the greatest (P < 0.05) NH3 1, 2, 4, 8, and 12 hours after feeding with steers fed Req-RDP being intermediate (P ≤ 0.05) at hour 1 and 2. Feeding decreased levels of RDP in experiment 1 did not reduce feedlot performance. Feeding increased levels of RDP resulted in greater N excretion as urea in the urine and reductions in RDP supplementation did not negatively impact rumen fermentation.
Issue Date:2019-12-13
Rights Information:Copyright 2019 Brady Joseph Klatt
Date Available in IDEALS:2020-03-02
Date Deposited:2019-12

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