- Open Access
Influence of ruminal degradable intake protein restriction on characteristics of digestion and growth performance of feedlot cattle during the late finishing phase
© May et al.; licensee BioMed Central Ltd. 2014
- Received: 29 April 2014
- Accepted: 16 July 2014
- Published: 13 August 2014
Two trials were conducted to evaluate the influence of supplemental urea withdrawal on characteristics of digestion (Trial 1) and growth performance (Trial 2) of feedlot cattle during the last 40 days on feed. Treatments consisted of a steam-flaked corn-based finishing diet supplemented with urea to provide urea fermentation potential (UFP) of 0, 0.6, and 1.2%. In Trial 1, six Holstein steers (160 ± 10 kg) with cannulas in the rumen and proximal duodenum were used in a replicated 3 × 3 Latin square experiment. Decreasing supplemental urea decreased (linear effect, P ≤ 0.05) ruminal OM digestion. This effect was mediated by decreases (linear effect, P ≤ 0.05) in ruminal digestibility of NDF and N. Passage of non-ammonia and microbial N (MN) to the small intestine decreased (linear effect, P = 0.04) with decreasing dietary urea level. Total tract digestion of OM (linear effect, P = 0.06), NDF (linear effect, P = 0.07), N (linear effect, P = 0.04) and dietary DE (linear effect, P = 0.05) decreased with decreasing urea level. Treatment effects on total tract starch digestion, although numerically small, likewise tended (linear effect, P = 0.11) to decrease with decreasing urea level. Decreased fiber digestion accounted for 51% of the variation in OM digestion. Ruminal pH was not affected by treatments averaging 5.82. Decreasing urea level decreased (linear effect, P ≤ 0.05) ruminal N-NH and blood urea nitrogen. In Trial 2, 90 crossbred steers (468 kg ± 8), were used in a 40 d feeding trial (5 steers/pen, 6 pens/ treatment) to evaluate treatment effects on final-phase growth performance. Decreasing urea level did not affect DMI, but decreased (linear effect, P ≤ 0.03) ADG, gain efficiency, and dietary NE. It is concluded that in addition to effects on metabolizable amino acid flow to the small intestine, depriving cattle of otherwise ruminally degradable N (RDP) during the late finishing phase may negatively impact site and extent of digestion of OM, depressing ADG, gain efficiency, and dietary NE.
- Degradable protein
- Growth performance
Because of its low cost per unit of N compared with most sources of natural protein, urea is a primary source of supplemental N in conventional steam-flaked corn-based finishing diets for feedlot cattle . In a review of nutrition consultant recommendations across 11 states in the USA, Vasconcelos and Galyean  observed that on average, flaked corn-based finishing diets contained 13.5% CP with 1.2% of supplemental urea (approximately 64% DIP). Although dietary formulation in this manner is expected to meet urea fermentation potential (UFP) for optimal microbial growth, it may exceed protein requirements for cattle growth, particularly during the late finishing phase. Preston  proposed the feasibility of restricting protein supplementation during the late finishing phase as a means of minimizing N excess and associated environmental impact [1, 4] without detrimentally affecting cattle performance. However, the impact of this practice on digestive function and cattle growth-performance has received limited research attention. The aim of this study was to evaluate the influence of UFP for optimal microbial growth on characteristics of digestion and growth performance of feedlot cattle during the late finishing phase.
All procedures involving animal care and management were in accordance with and approved by the University of California, Davis, Animal Use and Care Committee.
Diet composition of experiment 1 and 2 1
Urea fermentation potential
Ingredient (g/kg of DM)
Steam flaked corn
Trace mineral salt2
Nutrient composition (DM basis)4
RDP (g/kg of CP)
where: Yijk is the response variable, μ is the common experimental effect, Rl is the replicated effect, Si is the steer effect within replicate, Pj is the period effect within replicate, Tk is the treatment effect and Eijk is the residual error. Treatment effects were tested using the following contrasts: 1) linear effect of the urea level, and 2) quadratic effect of the urea level, which were determined according to SAS (SAS Inst., Inc., Cary, NC; Version 9.1).
Ninety crossbred steers with an average initial weight of 468 ± 8 kg were used in a 40 d finishing trial to evaluate the treatment effects on growth performance. Steers had a purchase weight of 214 ± 14 kg and had been on feed 197 d before initiation of the study. Steers had been implanted with Synovex-S (Zoetis, Florham Park, NJ) upon arrival into the feedlot and with Revalor-S (Merck Animal Health, Summit, NJ) on d 98. Ten d prior to initiation of the study steers were weighed, reimplanted with Revalor-S, blocked by weight and randomly allotted within weight groupings to 18 pens (5 steers/pen). Pens were 43 m2, with 22 m2 of overhead shade, automatic waterers, and 2.4 m long fence-line feed bunks. Dietary treatments were the same as those used in Experiment 1. All steers received the UFP-0 diet for 10 d prior to initiation of the trial. Diets were prepared at weekly intervals and stored in plywood boxes located in front of each pen. Steers were allowed free access to dietary treatments. Fresh feed was provided twice daily. Individual steers were weighed upon initiation and completion of the trial. In the calculation of steer performance live weights were reduce 4% to adjust for digestive tract fill. Estimates of steer performance were based on pen means. Net energy values for each diet were calculated from estimates of energy gain (EG, Mcal/d) based on growth-performance; EG = 0.0557 BW0.75 (ADG1.097), where EG is the daily energy deposited (Mcal/d), BW is the mean shrunk body weight (full weight × 0.96) and maintenance energy expended (EM, Mcal/d); EM = 0.077 BW0.75. Dietary NEg was derived from NEm by the equation: NEg = 0.877 NEm - 0.41 . Dry matter intake is related to energy requirements and dietary NEm according to the equation: DMI = EG / NEg), and can be resolved for estimation of dietary NE by means of the quadratic formula: , where x = NEm, a = -0.877 DMI, b = 0.877 EM + 0.41 DMI + EG, and c = -0.41 EM .
All steers were harvested on the same day. Each carcass was weighed at time of slaughter to determine dressing percentage . Performance (gain, gain efficiency, and dietary energetics) and carcass data were analyzed as a randomized complete block design; the experimental unit was the pen. The MIXED procedure of SAS  was used to analyze the variables. The fixed effect consisted of treatment, and pen was the random component. Treatments effects were tested using the following contrasts: 1) linear effect of the urea level, and 2) quadratic effect of the urea level, which were determined according to SAS .
Influence of dietary treatments on characteristics of digestion
Urea fermentation potential
P - value
Flow to the duodenum (g/d)
Ruminal digestibility, %
Fecal excretion (g/d)
Postruminal digestibility (% of flow to duodenum)
Total tract digestibility (% of intake)
Passage of non-ammonia N to the small intestine decreased (linear effect, P = 0.04) with decreasing dietary urea level. This effect was due to decreased (linear effect, P = 0.04) MN synthesis. Taking into consideration energy intake alone, predicted flow of MN to the small intestine was 48g/d (, Level 1). Accordingly, with decreasing urea level, the observed flow of MN to the small intestine was 85, 73, and 65% of predicted flow for UFP-0, UFP-0.6, and UFP-1.2, respectively. This decline in net synthesis is consistent with  who observed that MN flow to the small intestine declines with decreasing DIP below 100 g/kg of total tract digestible OM. For the present study, DIP averaged 95, 81, and 61g/kg total tract digestible OM for UFP-0, UFP-0.6, and UFP-1.2, respectively. Thus, it is apparent that as DIP intake drops below 95 g/kg digestible OM there is not sufficient compensation in ruminal N recycling to maintain microbial growth, and as microbial growth declines, likewise, ruminal OM digestion declines.
There were no treatment effects (P = 0.20) on passage of feed N to the small intestine. Notwithstanding decreased non-ammonia N flow to the small intestine with decreasing urea level, ruminal N efficiency (non-ammonia N flow to the small intestine as a fraction of N intake) increased (linear P < 0.05), reflecting increased contribution of recycled N into microbial protein synthesis, consistent with the observation that ruminal N flux increases inversely with dietary N concentration . Observed DIP (Table 2) averaged 103% of expected based on tabular values (; Table 1) for the three dietary treatments.
Total tract digestion of OM (linear effect, P = 0.06), NDF (linear effect, P = 0.07), N (linear effect, P = 0.04) and dietary DE (linear effect, P = 0.05) decreased with decreasing urea level. Treatment effects on total tract starch digestion, although numerically small, likewise tended (linear effect, P = 0.11) to decrease with decreasing urea level. Decreased fiber digestion accounted for 51% of the variation in OM digestion. In a previous study involving steam-flaked corn-based finishing diets in which urea was the sole source of supplemental N , increasing urea level from 1.0 to 1.6% of the steam-flaked corn in the diet (an upper level similar to that of the present study; Table 1) likewise enhanced total tract OM and fiber digestion. In contrast Zinn and Shen  observed removal of urea from a steam-flaked corn-based growing-finishing diet markedly depressed ruminal OM digestion and flow of MN to the small intestine but did not affect total tract OM digestion. Treatment effects on apparent N digestion were largely a function of the N content of the diet brought about by changes in dietary urea level .
Treatment effects on ruminal pH, VFA molar proportions and BUN
Urea fermentation potential
P – value
Ruminal N-NH (mg/dL)
Total VFA (mM)
Ruminal VFA (mol/100 mol)
Decreasing urea level decreased (linear effect, P < 0.01) ruminal N-NH. The N-NH concentration has been reported to increase immediately after feeding for 2 to 3 h [28, 29]. Satter and Roffler  observed a close relationship (R2 = 0.92) between the level of dietary CP and ruminal N-NH concentration at given dietary TDN. Likewise, in the present study dietary CP explained 88% of the variation ruminal N-NH concentration. Blood urea nitrogen (BUN) concentration 4 h postprandium also decreased (linear effect, P < 0.01) with decreasing urea supplementation. Blood urea nitrogen is also closely associated dietary CP and ruminal N-NH concentrations [31, 32]. Consistent with Zinn et al., decreasing urea level increased ruminal acetate:propionate molar ratio (linear effect, P = 0.05), and estimated methane production (mol/mol glucose equivalent fermented; linear effect, P = 0.04).
Treatment effects on growth performance and carcass weight of feedlot steers
Urea fermentation potential
Days on test
Live weight (kg)1
Diet NE (Mcal/kg)
Treatment effects on metabolizable protein and amino acid supply 1 versus requirements 2
Urea fermentation potential
Metabolizable protein, g/d
Metabolizable methionine, g/d
Metabolizable lysine, g/d
It is concluded that in addition to effects on net protein flow to the small intestine, depriving cattle of otherwise RDP during the late finishing phase may negatively impact site and extent of OM digestion, depressing ADG, gain efficiency, and dietary NE.
- Vasconcelos JT, Cole NA, McBride KW, Gueye A, Galyean ML, Richardson CR, Greene LW: Effects of dietary crude protein and supplemental urea levels on nitrogen and phosphorus utilization by feedlot cattle. J Anim Sci. 2009, 87: 1174-1183.View ArticlePubMedGoogle Scholar
- Vasconcelos JT, Galyean ML: Nutritional recommendations of feedlot consulting nutritionists: The 2007 Texas Tech University survey. J Anim Sci. 2007, 85: 2772-2781. 10.2527/jas.2007-0261View ArticlePubMedGoogle Scholar
- Preston RL: Empirical value of the crude protein systems for feedlot cattle. Protein Requirements for Cattle: Symposium. Edited by: Owens FN. 1982, 201-217. Stillwater, OK: Oklahoma Experimental Station MP-109, Oklahoma State University,Google Scholar
- Hristov AN, Hanigan M, Cole A, Todd R, McAllister TA, Ndegwaand PM, Rotz A: Review: Ammonia emissions from dairy farms and beef feedlots. Can J Anim Sci. 2011, 91: 1-35. 10.4141/CJAS10034.View ArticleGoogle Scholar
- Zinn RA, Plascencia A: Interaction of whole cottonseed and supplemental fat on digestive function in cattle. J Anim Sci. 1993, 71: 11-17.PubMedGoogle Scholar
- Burroughs W, Nelson DK, Mertens DR: Protein physiology and its application in the lactating cow: The metabolizable protein feeding standard. J Anim Sci. 1975, 41: 933-944.PubMedGoogle Scholar
- Fawcett JK, Scott JE: A rapid and precise method for the determination of urea. J Clin Pathol. 1960, 13: 156-159. 10.1136/jcp.13.2.156View ArticlePubMedPubMed CentralGoogle Scholar
- Bergen WG, Purser DB, Cline JH: Effect of ration on the nutritive quality of rumen microbial protein. J Anim Sci. 1968, 27: 1497-1501.Google Scholar
- , : Official methods of analysis. 2000, Gaithersburg, MD: Association Official Analytical Chemists, 17,Google Scholar
- Van Soest PJ, Robertson JB, Lewis BA: Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J Dairy Sci. 1991, 74: 3583-3597. 10.3168/jds.S0022-0302(91)78551-2View ArticlePubMedGoogle Scholar
- Zinn RA, Owens FN: A rapid procedure for purine measurement and its use for estimating net ruminal protein synthesis. Can J Anim Sci. 1986, 66: 157-166. 10.4141/cjas86-017.View ArticleGoogle Scholar
- Zinn RA: Influence of steaming time on site digestion of flaked corn in steers. J Anim Sci. 1990, 68: 776-781.PubMedGoogle Scholar
- Zinn RA: Comparative feeding value of supplemental fat in finishing diets for feedlot steers supplemented with and without monensin. J Anim Sci. 1988, 66: 213-227.PubMedGoogle Scholar
- Hill FN, Anderson DL: Comparison of metabolizable energy and productive determinations with growing chicks. J Nutr. 1958, 64: 587-603.PubMedGoogle Scholar
- Ørskov ER, MacLeod NA, Kyle DJ: Flow of nitrogen from the rumen and abomasum in cattle and sheep given protein-free nutrients by intragrastric infusion. Br J Nutr. 1986, 56: 241-248. 10.1079/BJN19860103View ArticlePubMedGoogle Scholar
- Wolin MJ: A theorical rumen fermentation balance. J Dairy Sci. 1960, 43: 1452-1459. 10.3168/jds.S0022-0302(60)90348-9.View ArticleGoogle Scholar
- , : Nutrient Requirements of Beef Cattle. 1996, Washington, DC: National Academy of Press, 7Google Scholar
- , : Nutrient Requirements of Beef Cattle. 1984, Washington, DC: National Academy Press, 6Google Scholar
- Zinn RA, Shen Y: An evaluation of ruminally degradable intake protein and metabolizable amino acid requirements of feedlot calves. J Anim Sci. 1998, 76: 1280-1289.PubMedGoogle Scholar
- , : United States Standards for Grading of Carcass Beef. 1997, Washington, DC: Agricultural Marketing Service, United States Department of AgricultureGoogle Scholar
- , : SAS/STAT User’s Guide: Version 9.1. 2004, Cary, North Caroline: SAS Institute Inc,Google Scholar
- Zinn RA, Borquez JL, Plascencia A: Influence of levels of supplemental urea on characteristics of digestion and growth performance of feedlot steers fed a fat-supplemented high-energy diets. Prof Anim Sci. 1994, 10: 5-10.Google Scholar
- Muscher AS, Schroder B, Breves G, Huber K: Dietary nitrogen reduction enhances urea transport across goat rumen epithelium. J Anim Sci. 2010, 88: 3390-3398. 10.2527/jas.2010-2949View ArticlePubMedGoogle Scholar
- Holter JA, Reid JT: Relationship between the concentrations of crude protein and apparently digestible protein in forages. J Anim Sci. 1959, 18: 1339-1349.Google Scholar
- Zinn RA, Barrajas R, Montaño M, Ware RA: Influence of dietary urea level on digestive function and growth performance of cattle fed steam-flaked barley- based finishing diets. J Anim Sci. 2003, 81: 2383-2389.PubMedGoogle Scholar
- Milton CT, Brandt RT, Titgemeyer EC: Urea in dry rolled corn diets: Finishing steers performance, nutrient digestion and microbial protein production. J Anim Sci. 1997, 75: 1415-1424.PubMedGoogle Scholar
- Brake DW, Titgemeyer EC, Jones ML, Anderson DE: Effect of nitrogen supplementation on urea kinetics and microbial use of recycled urea in steers consuming corn-based diets. J Anim Sci. 2010, 88: 2729-2740. 10.2527/jas.2009-2641View ArticlePubMedGoogle Scholar
- Chumpawadee S, Sommart K, Vongpralub T, Pattarajinda V: Effects of synchronizing the rate of dietary energy and nitrogen release on ruminal fermentation, microbial protein synthesis, blood urea nitrogen and nutrient digestibility in beef cattle. Asian-Australasian J Anim Sci. 2006, 19: 181-188.View ArticleGoogle Scholar
- Seo JK, Yang JY, Kim HJ, Upadhaya SD, Cho WM, Ha JK: Effects of synchronization of carbohydrate and protein supply on ruminal fermentation, nitrogen metabolism and microbial protein synthesis in Holstein steers. Asian-Aust J Anim Sci. 2010, 23: 1455-1461. 10.5713/ajas.2010.10247.View ArticleGoogle Scholar
- Satter LD, Roffler RE: Nitrogen requirements and utilization in dairy cattle. J Dairy Sci. 1975, 58: 1219-1237. 10.3168/jds.S0022-0302(75)84698-4View ArticlePubMedGoogle Scholar
- Hammond AC: Effect of dietary protein level, ruminal protein solubility and time after feeding on plasma urea nitrogen and the relationship of plasma urea nitrogen to other ruminal and plasma parameters. J Anim Sci. 1983, 57 (1): 435Google Scholar
- Hennessy DW, Nolan JV: Nitrogen kinetics in cattle fed a mature subtropical grass hay with and without protein meal supplementation. Aust J Agric Res. 1988, 39: 1135-1150. 10.1071/AR9881135.View ArticleGoogle Scholar
- Tedeschi LO, Baker MJ, Ketchen DJ, Fox DG: Performance of growing and finishing cattle supplemented with a slow-release urea product and urea. Can J Anim Sci. 2002, 82: 567-573. 10.4141/A02-018.View ArticleGoogle Scholar
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