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Effects of Oscillating Dietary Protein on Growth, Efficiency, and Serum Metabolites in Growing Beef Steers
30
The Professional Animal Scientist Ludden et al. 19 (2003):30–34
Effects of Oscillating Dietary Protein on Growth, Efficiency, and Serum Metabolites in Growing Beef Steers P. A. LUDDEN1 , PAS, T. L. WECHTER, E. J. SCHOLLJEGERDES, and B. W. HESS, PAS Department of Animal Sciences, University of Wyoming, Laramie, WY 82071-3684
Abstract Ninety-six Gelbvieh-Angus steers (average initial BW = 270 ± 0.5 kg) were used in a randomized complete blockdesign 56-d experiment to evaluate the effects of oscillating dietary CP on growth and serum metabolite concentrations in growing beef steers. The four treatments consisted of an 11, 13, or 15% CP diet fed daily or a regimen in which dietary CP was oscillated between 11 and 15% on a 48-h basis (ACP). All diets consisted of 65% bromegrass hay (8.9% CP, 61% NDF, and 37% ADF) plus 35% corn-based supplement and were formulated to contain ruminally degradable protein (RDP) at 8.5% of DM using a combination of soybean meal and urea. Treatment CP concentrations >11% were accomplished with the addition of a ruminally undegradable protein (RUP) source (SoyPLUS®; West Central Cooperative, Ralston, IA). All steers were fed at 3.0% of BW (DM basis) throughout the trial, resulting in an average DMI of 8.6 kg/d across treatments. Increasing CP from 11 to 15% linearly increased (P=0.007) ADG, which was associated with a linear increase (P=0.008) in feed
efficiency (kg of BW gain/100 kg of DM). Conversely, increasing dietary CP decreased (quadratic, P=0.02) efficiency of CP use (kg of BW gain/kg of CP intake) and increased (P=0.0001) serum urea N (SUN) concentrations. Steers fed ACP exhibited similar (P≤0.43) ADG and feed efficiency compared with those fed 13% CP daily. However, feeding ACP tended (P=0.13) to improve efficiency of CP use (1.00 vs 0.93 kg of BW gain/kg of CP intake) and tended (P=0.07) to reduce SUN compared with feeding the 13% CP diet daily. These results suggest that oscillating the CP concentration in the diet has little effect on steer performance and may increase efficiency of protein utilization compared with steers fed the same quantity of protein on a daily basis. (Key Words: Oscillating Dietary Protein, Ruminally Undegradable Protein, Growth, Serum Urea Nitrogen, Beef Cattle.)
Introduction
A common practice among range livestock producers is to supplement protein on alternate days to reduce expensive labor and equipment costs (22) while producing little detrimental effect on animal BW gain, body 1To whom correspondence should be adcondition score, or reproductive dressed: [email protected] performance (11, 12). The bulk of
such research examining the effects of protein supplementation frequency have been conducted with supplements high in ruminally degradable protein (RDP) because of the positive relationship between RDP supplementation and forage utilization (14). However, Collins and Pritchard (7) observed that alternate day supplementation of a cornstalkbased diet with ruminally undegradable protein (RUP; corn gluten meal) improved N retention of lambs compared with supplementation of RDP (soybean meal). Similarly, Cole (6) found that oscillating the CP content of the diet at 48-h intervals resulted in improved N retention in lambs fed a high concentrate diet, which was further enhanced with provision of natural protein vs urea. Because intermittent protein supplementation has been suggested to enhance N utilization by stimulating recycling of endogenous N to the rumen (11, 15), our hypothesis is that intermittent supplementation with RUP may further enhance N utilization by providing the animal with a sustained source of recyclable N. This study was conducted to determine the effects of oscillating dietary protein concentrations with RUP on growth, feed efficiency, and serum metabolite concentrations in growing beef steers.
Oscillating Dietary Protein for Growing Beef Steers
Materials and Methods
dietary CP was oscillated between 11 and 15% on a 48-h basis (i.e., 11, 11, Ninety-six growing Gelbvieh-Angus 15, 15, 11, 11,…). All diets were steers (270 ± 0.5 kg) were used in a 56- formulated to contain the same d randomized complete block-design amount of RDP (8.5% of DM) using a experiment. The steers were blocked combination of soybean meal and by initial BW and housed in one of urea. This level was chosen because 16 pens (six steers per pen) at the other research with similar forages University of Wyoming Animal has demonstrated that RDP at this Science Livestock Center (Laramie, level will support maximal forage WY). All animal care followed digestion (10, 17). Crude protein procedures that were approved by the concentrations above 11% were University of Wyoming Animal Care accomplished with the addition of a and Use Committee. The steers were RUP source (SoyPLUS®; West Central Cooperative, Ralston, IA). Experifed a basal diet consisting of 65% mental diets were fed at 3.0% of BW chopped (2.54 cm) bromegrass hay (DM basis) once daily at 1600 h, and (8.9% CP, 61% NDF, and 37% ADF) all protein supplements (35% of diet and 35% corn-based supplement DM) were top-dressed at feeding. The (Table 1). Four dietary treatments consisted of an 11, 13, or 15% CP diet quantity of feed offered was adjusted for changes in BW at d 28. fed daily or a regimen in which
TABLE 1. Composition of diets. Diet (% CP)a Item Ingredient, % of DM Chopped bromegrass hay Cracked corn Soybean meal SoyPLUS®b Urea Dicalcium phosphate Limestone Magnesium sulfate Trace-mineralized saltc Vitamin premixd Chemical composition DM, % OM, % of DM CP, % of DM NDF, % of DM ADF, % of DM aDietary
11
13
65.0 26.4 5.4
65.0 20.8 3.9 7.4
65.0 15.6 1.4 15.3
0.1 0.2 0.9 1.0 0.5 0.5
0.1 0.9 0.9 0.5 0.5
1.0 0.7 0.5 0.5
88.9 91.1 11.2 43.9 25.8
89.0 90.8 13.7 43.5 26.0
89.2 90.9 15.2 43.2 26.4
treatments consisted of the 11, 13, or 15% CP diet fed daily or the 11 and 15% CP diets alternated every 48 h (ACP). bWest Central Cooperative (Ralston, IA). cContained 98.0% NaCl, 0.35% Zn, 0.28% Mg, 0.175% Fe, 0.035% Cu, and 0.028% I. dContained 17,636,800 IU of vitamin A, 1,763,680 IU of vitamin D3, and 88,184 IU of vitamin E/kg.
15
31
Steer BW was taken approximately 1 h before the daily feeding on 2 consecutive d at the beginning, on d 28, and on 2 consecutive d at the end of the trial. Blood samples (10 mL) were collected via tailhead venipuncture on 4 consecutive d at the end of the trial at approximately 1 h before the daily feeding. Blood was immediately refrigerated, allowed to clot for 24 h, and centrifuged at 2,000 × g for 20 min. The resulting serum was frozen for later analyses of serum urea N (SUN; Kit No. 535; Sigma Diagnostics, St. Louis, MO) and glucose concentrations (Kit No. 635; Sigma Diagnostics). Feed samples were collected at 14-d intervals throughout the trial and were analyzed for DM, OM, and Kjeldahl N (1) and NDF and ADF content (19). All steer performance data were analyzed using the GLM procedure of SAS (SAS Inst. Inc., Cary, NC) for a randomized complete block design using pen as the experimental unit. Single degree of freedom orthogonal contrasts were used to determine linear and quadratic effects of protein concentration in the diet and for the 13% CP diet fed daily vs ACP treatment. Blood metabolite data were analyzed using the REPEATED statement within the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC). The model included the effects of block, pen, treatment, day, and treatment × day. Block × pen × treatment was used to specify variation between animals (pens) using the RANDOM statement. Block × pen × treatment was used as the SUBJECT, and autoregression was used as the covariance structure. The same contrasts described previously were used to partition the treatment sums of squares.
Results and Discussion Because steers were fed at 3.0% of BW throughout the trial, DMI did not differ (P=0.14) and averaged 8.65 ± 0.5 kg/d across treatments (Table 2). Increasing CP from 11 to 15% linearly increased (P=0.007) ADG, resulting in a linear increase (P=0.008)
32
Ludden et al.
in efficiency (kg of gain/100 kg of feed). However, efficiency of CP use (kg of BW gain/kg of CP intake) decreased quadratically (P=0.02) with increasing dietary CP. The improved efficiency of CP use for the 11% CP treatment suggests that dietary protein likely limited growth for those steers, resulting in the conservation of protein by the animal. Such a response could be via improved efficiency of amino acid utilization for protein deposition (8, 18) or enhanced recycling of endogenous N to the rumen for use in microbial metabolism and subsequent forage digestion (2, 11, 15). Steers fed ACP had similar ADG (P=0.55) and feed efficiency (kg of gain/100 kg of DMI; P = 0.43) compared with those fed the 13% CP diet daily, suggesting that ACP was not detrimental to animal performance. This response is similar to the results of previous research demonstrating that feeding supplemental protein at up to weekly intervals to ruminants consuming forage is not detrimental to animal performance (2, 12, 22). We also observed that ACP-fed steers tended (P=0.13) to have improved efficiency of CP use (kg of gain/kg of CP intake) compared with those fed 13% CP daily. Other researchers have
reported similar improvements in growth or efficiency with intermittent supplementation. Hunt et al. (11) reported improved ADG of steers consuming low quality forage and supplemented cottonseed meal every 48 h compared with those supplemented with the same quantity of protein on a daily basis. Collins and Pritchard (7) observed that alternate day protein supplementation improved N retention of lambs consuming low quality cornstalk-based diets. These researchers further observed that providing a supplement high in RUP (corn gluten meal) resulted in a greater improvement in N retention than when a high RDP supplement (soybean meal) was fed. Cole (6) reported that oscillating the CP content of the diet at 48-h intervals (as was done in our experiment) with cottonseed meal improved N retention in lambs fed a high concentrate diet; however, this improvement was lessened when a portion of the supplemental protein was replaced by non-protein N (urea). No treatment × day interaction (P=0.79) was noted for serum glucose concentrations, and, thus, only overall treatment means are presented in Table 2. Mean serum glucose concentrations were similar (P=0.52)
in steers fed ACP compared with those fed 13% CP daily. However, increasing dietary protein tended (P=0.10) to linearly increase serum glucose concentrations. SletmoenOlson et al. (20) reported that gestating cows fed a supplement high in RUP had greater plasma glucose concentrations than cows fed a medium RUP supplement. Because up to 30% of blood glucose can be derived from amino acid carbon (9, 23), perhaps a greater portion of absorbed amino acids contributed to glucose synthesis, because dietary protein was increased using RUP in our experiment. We further observed that increasing dietary CP linearly increased (P=0.0001) mean SUN concentrations (Table 2), which supports our contention that a portion of the supplemental RUP might have been catabolized rather than used for tissue protein deposition. Other researchers (5, 20, 21) have observed similar increases in SUN with provision of supplemental RUP. Steers fed ACP tended (P=0.07) to have less mean SUN than those receiving 13% CP daily (Table 2). However, a treatment × day interaction (P=0.0001) occurred in SUN; SUN of the ACP-fed steers was less in
TABLE 2. Performance and serum metabolites of steers fed increasing dietary protein or oscillating dietary protein concentrations. Treatmenta Item
11
Initial BW, kg Final BW, kg ADG, kg DMI, kg/d kg of BW gain/100 kg of DMI kg of BW gain/kg of CP intake Serum glucose, mg/dL Serum urea N, mg/dLc
269.6 329.4 1.07 8.58 12.5 1.11 80.8 4.97
13 270.7 332.5 1.10 8.67 12.7 0.93 85.0 7.68
15 270.6 340.3 1.25 8.70 14.3 0.94 88.0 10.54
Contrastb ACP
SEM
L
Q
ACP
270.8 334.4 1.14 8.64 13.2 1.00 85.3 6.64
1.35 2.46 0.04 0.50 0.39 0.03 2.89 0.37
0.65 0.01 0.007 0.14 0.008 0.002 0.10 0.0001
0.74 0.45 0.27 0.65 0.19 0.02 0.44 0.12
0.95 0.59 0.55 0.64 0.43 0.13 0.52 0.07
a11, 13, or 15% CP diet fed daily or the 11 and 15% CP diets alternated every 48 h (ACP). bL
= Linear effect of increasing CP, Q = Quadratic effect of increasing CP, and ACP = ACP vs 13% CP fed daily. × day interaction (P=0.0001; see Figure 1).
cTreatment
Oscillating Dietary Protein for Growing Beef Steers
33
to 6-d intervals did not affect forage intake or OM, N, or fiber digestibility compared with daily supplementation and that this response was independent of ruminal protein degradability. Although it may seem illogical to supplement RUP when RDP is most likely to be the limiting nutrient, we hypothesize that RUP supplementation may indirectly stimulate N recycling on the day following supplementation. Our hypothesis is that providing protein in the form of RUP in the ACP treatment might have provided a Figure 1. Treatment × day interaction (P=0.0001) in serum urea N concentrations of steers time-delay source of RDP via N fed increasing dietary CP or oscillating CP concentrations. ! = 11% CP diet fed daily, " = 13% CP diet fed daily, # = 15% CP diet fed daily, 䉱 = 11 and 15% CP diets oscillated on a recycling (16). On days following 48-h basis (ACP). Samples collected on d 1 and 4 for the ACP treatment represent serum urea when ACP-fed steers were fed 15% CP N concentrations 24 h after feeding the 15% CP diet, whereas d 2 and 3 represent 24 h after (d 1 and 4), their SUN concentration feeding the 11% CP diet. remained less than those fed 15% CP daily, possibly because of a decrease samples collected 24 h after feeding bromegrass hay supplemented soyin catabolism of amino acids by the the 11% CP diet and greater after bean meal once every 72 h sustained liver. Therefore, on days when the feeding the 15% CP diet (Figure 1). elevated ruminal ammonia N concen- 11% diet was fed, those amino acids When ACP-fed steers consumed the trations on the second day following circulating in the blood from the 11% CP diet, SUN concentrations supplementation because of a greater RUP may be deaminated and conresembled that of steers fed the 11% removal of urea N from the portal verted to urea by the liver. Such CP diet daily, but when fed the 15% drained viscera (PDV; the gastrointes- deamination of amino acids may CP diet, SUN concentrations were tinal tract, spleen, pancreas, and provide a time-delay mechanism in similar to those of steers fed 13% CP supporting connective and adipose urea synthesis, whereby blood urea daily rather than those fed 15% CP. tissue). This result suggests that on concentrations are increased to These results indicate a more efficient days without supplementation, coincide with decreased ruminal NH3 utilization of protein by ACP-fed increasing quantities of urea N were N concentrations on the day followsteers when the 15% CP diet was fed, recycled from the PDV to the rumen, ing supplementation. Because the thereby supporting our contention and that urea N recycling to the transfer of blood urea into the rumen that intermittent supplementation rumen was greatest when intake of N is affected by ruminal NH N and 3 may improve the efficiency of protein was low, which reveals the imporblood urea concentrations (13), utilization. tance of N recycling at low N intakes. providing a portion of the suppleIt is often suggested that infreThe bulk of research examining mental protein as RUP in supplequent protein supplementation may the effects of protein supplementaments fed intermittently may increase stimulate recycling of endogenous N tion frequency have been conducted the propensity for endogenously into the rumen (2, 11, 15). Evidence with supplements high in RDP synthesized urea to be recycled back for increased N recycling in rumibecause of the positive relationship to the rumen for use in microbial nants supplemented infrequently was between RDP supplementation and metabolism, thereby enhancing the provided by Beaty et al. (2), who forage utilization (14). Our results, efficiency of protein utilization by observed that steers consuming low and those of Collins and Pritchard the animal. However, the manner in quality forage supplemented with (7) and Cole (6), provide evidence which ruminal degradability of soybean meal three times weekly were that intermittent supplementation supplemental protein influences the able to sustain elevated ruminal with a protein source greater in RUP efficiency of protein use and/or N ammonia concentrations compared may further improve efficiency of N recycling in the infrequently supplewith steers supplemented daily, utilization by ruminants. However, mented ruminant animal deserves thereby maintaining a desirable data are limited comparing the effects further investigation. digestion environment and improved of RDP vs RUP supplemented at ruminal N status, even on days when infrequent intervals on endogenous supplement was not provided. N recycling and efficiency of N use. Similarly, Krehbiel et al. (15) conBohnert et al. (4) noted that infreOscillating dietary protein concencluded that ewes fed low quality quent protein supplementation at up trations has no detrimental effect on
Implications
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Ludden et al.
animal performance; thus, this feeding regimen can be used under practical feeding conditions and incorporated into supplementation programs with minimal impact on the performance of ruminant animals. Moreover, oscillating the protein concentration in the diet may provide producers with a management alternative that may ultimately decrease supplementation costs and improve economic returns. The mechanism(s) whereby ruminants are capable of maintaining performance under conditions of intermittent protein supplementation may be related to improvements in efficiency of protein utilization. Although such improvement is likely via enhanced recycling of endogenous nitrogen to the rumen, further research into the effects of intermittent protein supplementation on the dynamics of protein utilization in the ruminant is warranted.
Acknowledgments We gratefully acknowledge the assistance of Lane Ciminski, Dwayne Byerly, and the University of Wyoming Beef Farm for their assistance with feeding, animal care, and sample collection associated with this project. We also thank West Central Cooperative (Ralston, IA) for donation of the SoyPLUS® used in this project. This research was supported in part by the University of Wyoming Faculty Grant-In-Aid Program.
Literature Cited 1. AOAC. 1990. Official Methods of Analysis. (15th Ed.). Association of Official Analytical Chemists, Arlington, VA. 2. Beaty, J. L., R. C. Cochran, B. A. Lintzenich, E. S. Vanzant, J. L. Morrill, R. T. Brandt, Jr., and D. E. Johnson. 1994. Effect
of frequency of supplementation and protein concentration in supplements on performance and digestion characteristics of beef cattle consuming low-quality forages. J. Anim. Sci. 72:2475. 3. Bohnert, D. W., C. S. Schauer, and T. DelCurto. 2002. Influence of rumen protein degradability and supplementation frequency on performance and nitrogen use in ruminants consuming low-quality forage: Cow performance and efficiency of nitrogen use in wethers. J. Anim. Sci. 80:1629. 4. Bohnert, D. W., C. S. Schauer, M. L. Bauer, and T. DelCurto. 2001. Influence of rumen protein degradability and supplementation frequency on steers consuming low-quality forage: Ruminal fermentation and site of digestion. Proc. West. Sec. Am. Soc. Anim. Sci. 52:311. 5. Caton, J. S., V. I. Burke, P. Norton, L. A. Burgwald-Balstad, and K. E. Sletmoen. 1994. Influence of increasing level of escape protein supplementation on in situ disappearance, plasma hormones, and metabolites and microbial efficiency in steers fed low-quality grass hay. Proc. West. Sec. Am. Soc. Anim. Sci. 45:205. 6. Cole, N. A. 1999. Nitrogen retention in lambs fed oscillating dietary protein concentrations. J. Anim. Sci. 77:215. 7. Collins, R. M., and R. H. Pritchard. 1992. Alternate day supplementation of corn stalks diets with soybean meal or corn gluten meal fed to ruminants. J. Anim. Sci. 70:3899. 8. Heger, J., and Z. Frydrych. 1989. Efficiency of utilization of amino acids. In Absorption and Utilization of Amino Acids. M. Friedman (Ed.). p 31. CRC Press, Boca Raton, FL. 9. Heitmann, R. N., W. H. Hoover, and C. J. Sniffen. 1973. Gluconeogenesis from amino acids in mature wether sheep. J. Nutr. 103:1587. 10. Hollingsworth-Jenkins, K. J., T. J. Klopfenstein, D. C. Adams, and J. B. Lamb. 1996. Ruminally degradable protein requirement of gestating beef cows grazing native winter sandhills range. J. Anim. Sci. 74:1343. 11. Hunt, C. W., J. F. Parkinson, R. A. Roeder, and D. G. Falk. 1989. The delivery of cottonseed meal at three different time intervals to steers fed low-quality grass hay: Effects on digestion and performance. J. Anim. Sci. 67:1360. 12. Huston, J. E., H. Lippke, T.D.A. Forbes, J. W. Holloway, and R. V. Machen. 1999. Effects of supplemental feeding interval on adult cows in western Texas. J. Anim. Sci. 77:3057. 13. Kennedy, P. M., and P. Milligan. 1980. The degradation and utilization of endogenous urea in the gastrointestinal tract of ruminants: A review. Can. J. Anim. Sci. 62:205.
14. Köster, H. H., R. C. Cochran, E. C. Titgemeyer, E. S. Vanzant, I. Abdelgadir, and G. St-Jean. 1996. Effect of increasing degradable intake protein on intake and digestion of low-quality, tallgrass-prairie forage by beef cows. J. Anim. Sci. 74:2473. 15. Krehbiel, C. R., C. L. Ferrell, and H. C. Freetly. 1998. Effects of frequency of supplementation on dry matter intake and net portal and hepatic flux of nutrients in mature ewes that consume low-quality forage. J. Anim. Sci. 76:2464. 16. Ludden, P. A., T. L. Wechter, and B. W. Hess. 2002. Effects of oscillating dietary protein on ruminal fermentation and site and extent of nutrient digestion in sheep. J. Anim. Sci. 80:3336. 17. Mathis, C. P., R. C. Cochran, J. S. Heldt, B. C. Woods, I.E.O. Abdelgadir, K. C. Olson, E. C. Titgemeyer, and E. S. Vanzant. 2000. Effects of supplemental degradable intake protein on utilization of medium- to lowquality forages. J. Anim. Sci. 78:224. 18. Oldham, J. D. 1994. Amino acid nutrition of the dairy cow. In Amino Acids in Farm Animal Nutrition. J.P.F. D’Mello (Ed.). p 351. CAB International, Wallingford, UK. 19. Robertson , J. B., and P. J. Van Soest. 1980. The detergent system of analysis and its application to human foods. In The Analysis of Dietary Fiber. W.P.T. James and O. Theander (Eds.). Marcell Dekker, New York, NY. 20. Sletmoen-Olson, K. E., J. S. Caton, K. C. Olson, D. A. Redmer, J. D. Kirsch, and L. P. Reynolds. 2000. Undegraded intake protein supplementation: II. Effects on plasma hormone and metabolic concentrations in periparturient beef cows fed low-quality hay during gestation and lactation. J. Anim. Sci. 78:456. 21. Swanson, K. C., J. S. Caton, D. A. Redmer, V .I. Burke, and L. P. Reynolds. 2000. Influence of undegraded intake protein on intake, digestion, serum hormones and metabolites, and nitrogen balance in sheep. Small Rum. Res. 35:225. 22. Wallace, J. D. 1988. Supplemental feeding options to improve livestock efficiency on rangelands. In Achieving Efficient Use of Rangeland Resources. Proc. of Fort Keogh Res. Symp. R. S. White and R. E. Short (Eds.). p 92. Montana Agric. Exp. Stn., Bozeman, MT. 23. Wolff, J. E., E. N. Bergman, and H. H. Williams. 1972. Net metabolism of plasma amino acids by liver and portal-drained viscera of fed sheep. Am. J. Phys. 223:438.
The Professional Animal Scientist Ludden et al. 19 (2003):30–34
Effects of Oscillating Dietary Protein on Growth, Efficiency, and Serum Metabolites in Growing Beef Steers P. A. LUDDEN1 , PAS, T. L. WECHTER, E. J. SCHOLLJEGERDES, and B. W. HESS, PAS Department of Animal Sciences, University of Wyoming, Laramie, WY 82071-3684
Abstract Ninety-six Gelbvieh-Angus steers (average initial BW = 270 ± 0.5 kg) were used in a randomized complete blockdesign 56-d experiment to evaluate the effects of oscillating dietary CP on growth and serum metabolite concentrations in growing beef steers. The four treatments consisted of an 11, 13, or 15% CP diet fed daily or a regimen in which dietary CP was oscillated between 11 and 15% on a 48-h basis (ACP). All diets consisted of 65% bromegrass hay (8.9% CP, 61% NDF, and 37% ADF) plus 35% corn-based supplement and were formulated to contain ruminally degradable protein (RDP) at 8.5% of DM using a combination of soybean meal and urea. Treatment CP concentrations >11% were accomplished with the addition of a ruminally undegradable protein (RUP) source (SoyPLUS®; West Central Cooperative, Ralston, IA). All steers were fed at 3.0% of BW (DM basis) throughout the trial, resulting in an average DMI of 8.6 kg/d across treatments. Increasing CP from 11 to 15% linearly increased (P=0.007) ADG, which was associated with a linear increase (P=0.008) in feed
efficiency (kg of BW gain/100 kg of DM). Conversely, increasing dietary CP decreased (quadratic, P=0.02) efficiency of CP use (kg of BW gain/kg of CP intake) and increased (P=0.0001) serum urea N (SUN) concentrations. Steers fed ACP exhibited similar (P≤0.43) ADG and feed efficiency compared with those fed 13% CP daily. However, feeding ACP tended (P=0.13) to improve efficiency of CP use (1.00 vs 0.93 kg of BW gain/kg of CP intake) and tended (P=0.07) to reduce SUN compared with feeding the 13% CP diet daily. These results suggest that oscillating the CP concentration in the diet has little effect on steer performance and may increase efficiency of protein utilization compared with steers fed the same quantity of protein on a daily basis. (Key Words: Oscillating Dietary Protein, Ruminally Undegradable Protein, Growth, Serum Urea Nitrogen, Beef Cattle.)
Introduction
A common practice among range livestock producers is to supplement protein on alternate days to reduce expensive labor and equipment costs (22) while producing little detrimental effect on animal BW gain, body 1To whom correspondence should be adcondition score, or reproductive dressed: [email protected] performance (11, 12). The bulk of
such research examining the effects of protein supplementation frequency have been conducted with supplements high in ruminally degradable protein (RDP) because of the positive relationship between RDP supplementation and forage utilization (14). However, Collins and Pritchard (7) observed that alternate day supplementation of a cornstalkbased diet with ruminally undegradable protein (RUP; corn gluten meal) improved N retention of lambs compared with supplementation of RDP (soybean meal). Similarly, Cole (6) found that oscillating the CP content of the diet at 48-h intervals resulted in improved N retention in lambs fed a high concentrate diet, which was further enhanced with provision of natural protein vs urea. Because intermittent protein supplementation has been suggested to enhance N utilization by stimulating recycling of endogenous N to the rumen (11, 15), our hypothesis is that intermittent supplementation with RUP may further enhance N utilization by providing the animal with a sustained source of recyclable N. This study was conducted to determine the effects of oscillating dietary protein concentrations with RUP on growth, feed efficiency, and serum metabolite concentrations in growing beef steers.
Oscillating Dietary Protein for Growing Beef Steers
Materials and Methods
dietary CP was oscillated between 11 and 15% on a 48-h basis (i.e., 11, 11, Ninety-six growing Gelbvieh-Angus 15, 15, 11, 11,…). All diets were steers (270 ± 0.5 kg) were used in a 56- formulated to contain the same d randomized complete block-design amount of RDP (8.5% of DM) using a experiment. The steers were blocked combination of soybean meal and by initial BW and housed in one of urea. This level was chosen because 16 pens (six steers per pen) at the other research with similar forages University of Wyoming Animal has demonstrated that RDP at this Science Livestock Center (Laramie, level will support maximal forage WY). All animal care followed digestion (10, 17). Crude protein procedures that were approved by the concentrations above 11% were University of Wyoming Animal Care accomplished with the addition of a and Use Committee. The steers were RUP source (SoyPLUS®; West Central Cooperative, Ralston, IA). Experifed a basal diet consisting of 65% mental diets were fed at 3.0% of BW chopped (2.54 cm) bromegrass hay (DM basis) once daily at 1600 h, and (8.9% CP, 61% NDF, and 37% ADF) all protein supplements (35% of diet and 35% corn-based supplement DM) were top-dressed at feeding. The (Table 1). Four dietary treatments consisted of an 11, 13, or 15% CP diet quantity of feed offered was adjusted for changes in BW at d 28. fed daily or a regimen in which
TABLE 1. Composition of diets. Diet (% CP)a Item Ingredient, % of DM Chopped bromegrass hay Cracked corn Soybean meal SoyPLUS®b Urea Dicalcium phosphate Limestone Magnesium sulfate Trace-mineralized saltc Vitamin premixd Chemical composition DM, % OM, % of DM CP, % of DM NDF, % of DM ADF, % of DM aDietary
11
13
65.0 26.4 5.4
65.0 20.8 3.9 7.4
65.0 15.6 1.4 15.3
0.1 0.2 0.9 1.0 0.5 0.5
0.1 0.9 0.9 0.5 0.5
1.0 0.7 0.5 0.5
88.9 91.1 11.2 43.9 25.8
89.0 90.8 13.7 43.5 26.0
89.2 90.9 15.2 43.2 26.4
treatments consisted of the 11, 13, or 15% CP diet fed daily or the 11 and 15% CP diets alternated every 48 h (ACP). bWest Central Cooperative (Ralston, IA). cContained 98.0% NaCl, 0.35% Zn, 0.28% Mg, 0.175% Fe, 0.035% Cu, and 0.028% I. dContained 17,636,800 IU of vitamin A, 1,763,680 IU of vitamin D3, and 88,184 IU of vitamin E/kg.
15
31
Steer BW was taken approximately 1 h before the daily feeding on 2 consecutive d at the beginning, on d 28, and on 2 consecutive d at the end of the trial. Blood samples (10 mL) were collected via tailhead venipuncture on 4 consecutive d at the end of the trial at approximately 1 h before the daily feeding. Blood was immediately refrigerated, allowed to clot for 24 h, and centrifuged at 2,000 × g for 20 min. The resulting serum was frozen for later analyses of serum urea N (SUN; Kit No. 535; Sigma Diagnostics, St. Louis, MO) and glucose concentrations (Kit No. 635; Sigma Diagnostics). Feed samples were collected at 14-d intervals throughout the trial and were analyzed for DM, OM, and Kjeldahl N (1) and NDF and ADF content (19). All steer performance data were analyzed using the GLM procedure of SAS (SAS Inst. Inc., Cary, NC) for a randomized complete block design using pen as the experimental unit. Single degree of freedom orthogonal contrasts were used to determine linear and quadratic effects of protein concentration in the diet and for the 13% CP diet fed daily vs ACP treatment. Blood metabolite data were analyzed using the REPEATED statement within the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC). The model included the effects of block, pen, treatment, day, and treatment × day. Block × pen × treatment was used to specify variation between animals (pens) using the RANDOM statement. Block × pen × treatment was used as the SUBJECT, and autoregression was used as the covariance structure. The same contrasts described previously were used to partition the treatment sums of squares.
Results and Discussion Because steers were fed at 3.0% of BW throughout the trial, DMI did not differ (P=0.14) and averaged 8.65 ± 0.5 kg/d across treatments (Table 2). Increasing CP from 11 to 15% linearly increased (P=0.007) ADG, resulting in a linear increase (P=0.008)
32
Ludden et al.
in efficiency (kg of gain/100 kg of feed). However, efficiency of CP use (kg of BW gain/kg of CP intake) decreased quadratically (P=0.02) with increasing dietary CP. The improved efficiency of CP use for the 11% CP treatment suggests that dietary protein likely limited growth for those steers, resulting in the conservation of protein by the animal. Such a response could be via improved efficiency of amino acid utilization for protein deposition (8, 18) or enhanced recycling of endogenous N to the rumen for use in microbial metabolism and subsequent forage digestion (2, 11, 15). Steers fed ACP had similar ADG (P=0.55) and feed efficiency (kg of gain/100 kg of DMI; P = 0.43) compared with those fed the 13% CP diet daily, suggesting that ACP was not detrimental to animal performance. This response is similar to the results of previous research demonstrating that feeding supplemental protein at up to weekly intervals to ruminants consuming forage is not detrimental to animal performance (2, 12, 22). We also observed that ACP-fed steers tended (P=0.13) to have improved efficiency of CP use (kg of gain/kg of CP intake) compared with those fed 13% CP daily. Other researchers have
reported similar improvements in growth or efficiency with intermittent supplementation. Hunt et al. (11) reported improved ADG of steers consuming low quality forage and supplemented cottonseed meal every 48 h compared with those supplemented with the same quantity of protein on a daily basis. Collins and Pritchard (7) observed that alternate day protein supplementation improved N retention of lambs consuming low quality cornstalk-based diets. These researchers further observed that providing a supplement high in RUP (corn gluten meal) resulted in a greater improvement in N retention than when a high RDP supplement (soybean meal) was fed. Cole (6) reported that oscillating the CP content of the diet at 48-h intervals (as was done in our experiment) with cottonseed meal improved N retention in lambs fed a high concentrate diet; however, this improvement was lessened when a portion of the supplemental protein was replaced by non-protein N (urea). No treatment × day interaction (P=0.79) was noted for serum glucose concentrations, and, thus, only overall treatment means are presented in Table 2. Mean serum glucose concentrations were similar (P=0.52)
in steers fed ACP compared with those fed 13% CP daily. However, increasing dietary protein tended (P=0.10) to linearly increase serum glucose concentrations. SletmoenOlson et al. (20) reported that gestating cows fed a supplement high in RUP had greater plasma glucose concentrations than cows fed a medium RUP supplement. Because up to 30% of blood glucose can be derived from amino acid carbon (9, 23), perhaps a greater portion of absorbed amino acids contributed to glucose synthesis, because dietary protein was increased using RUP in our experiment. We further observed that increasing dietary CP linearly increased (P=0.0001) mean SUN concentrations (Table 2), which supports our contention that a portion of the supplemental RUP might have been catabolized rather than used for tissue protein deposition. Other researchers (5, 20, 21) have observed similar increases in SUN with provision of supplemental RUP. Steers fed ACP tended (P=0.07) to have less mean SUN than those receiving 13% CP daily (Table 2). However, a treatment × day interaction (P=0.0001) occurred in SUN; SUN of the ACP-fed steers was less in
TABLE 2. Performance and serum metabolites of steers fed increasing dietary protein or oscillating dietary protein concentrations. Treatmenta Item
11
Initial BW, kg Final BW, kg ADG, kg DMI, kg/d kg of BW gain/100 kg of DMI kg of BW gain/kg of CP intake Serum glucose, mg/dL Serum urea N, mg/dLc
269.6 329.4 1.07 8.58 12.5 1.11 80.8 4.97
13 270.7 332.5 1.10 8.67 12.7 0.93 85.0 7.68
15 270.6 340.3 1.25 8.70 14.3 0.94 88.0 10.54
Contrastb ACP
SEM
L
Q
ACP
270.8 334.4 1.14 8.64 13.2 1.00 85.3 6.64
1.35 2.46 0.04 0.50 0.39 0.03 2.89 0.37
0.65 0.01 0.007 0.14 0.008 0.002 0.10 0.0001
0.74 0.45 0.27 0.65 0.19 0.02 0.44 0.12
0.95 0.59 0.55 0.64 0.43 0.13 0.52 0.07
a11, 13, or 15% CP diet fed daily or the 11 and 15% CP diets alternated every 48 h (ACP). bL
= Linear effect of increasing CP, Q = Quadratic effect of increasing CP, and ACP = ACP vs 13% CP fed daily. × day interaction (P=0.0001; see Figure 1).
cTreatment
Oscillating Dietary Protein for Growing Beef Steers
33
to 6-d intervals did not affect forage intake or OM, N, or fiber digestibility compared with daily supplementation and that this response was independent of ruminal protein degradability. Although it may seem illogical to supplement RUP when RDP is most likely to be the limiting nutrient, we hypothesize that RUP supplementation may indirectly stimulate N recycling on the day following supplementation. Our hypothesis is that providing protein in the form of RUP in the ACP treatment might have provided a Figure 1. Treatment × day interaction (P=0.0001) in serum urea N concentrations of steers time-delay source of RDP via N fed increasing dietary CP or oscillating CP concentrations. ! = 11% CP diet fed daily, " = 13% CP diet fed daily, # = 15% CP diet fed daily, 䉱 = 11 and 15% CP diets oscillated on a recycling (16). On days following 48-h basis (ACP). Samples collected on d 1 and 4 for the ACP treatment represent serum urea when ACP-fed steers were fed 15% CP N concentrations 24 h after feeding the 15% CP diet, whereas d 2 and 3 represent 24 h after (d 1 and 4), their SUN concentration feeding the 11% CP diet. remained less than those fed 15% CP daily, possibly because of a decrease samples collected 24 h after feeding bromegrass hay supplemented soyin catabolism of amino acids by the the 11% CP diet and greater after bean meal once every 72 h sustained liver. Therefore, on days when the feeding the 15% CP diet (Figure 1). elevated ruminal ammonia N concen- 11% diet was fed, those amino acids When ACP-fed steers consumed the trations on the second day following circulating in the blood from the 11% CP diet, SUN concentrations supplementation because of a greater RUP may be deaminated and conresembled that of steers fed the 11% removal of urea N from the portal verted to urea by the liver. Such CP diet daily, but when fed the 15% drained viscera (PDV; the gastrointes- deamination of amino acids may CP diet, SUN concentrations were tinal tract, spleen, pancreas, and provide a time-delay mechanism in similar to those of steers fed 13% CP supporting connective and adipose urea synthesis, whereby blood urea daily rather than those fed 15% CP. tissue). This result suggests that on concentrations are increased to These results indicate a more efficient days without supplementation, coincide with decreased ruminal NH3 utilization of protein by ACP-fed increasing quantities of urea N were N concentrations on the day followsteers when the 15% CP diet was fed, recycled from the PDV to the rumen, ing supplementation. Because the thereby supporting our contention and that urea N recycling to the transfer of blood urea into the rumen that intermittent supplementation rumen was greatest when intake of N is affected by ruminal NH N and 3 may improve the efficiency of protein was low, which reveals the imporblood urea concentrations (13), utilization. tance of N recycling at low N intakes. providing a portion of the suppleIt is often suggested that infreThe bulk of research examining mental protein as RUP in supplequent protein supplementation may the effects of protein supplementaments fed intermittently may increase stimulate recycling of endogenous N tion frequency have been conducted the propensity for endogenously into the rumen (2, 11, 15). Evidence with supplements high in RDP synthesized urea to be recycled back for increased N recycling in rumibecause of the positive relationship to the rumen for use in microbial nants supplemented infrequently was between RDP supplementation and metabolism, thereby enhancing the provided by Beaty et al. (2), who forage utilization (14). Our results, efficiency of protein utilization by observed that steers consuming low and those of Collins and Pritchard the animal. However, the manner in quality forage supplemented with (7) and Cole (6), provide evidence which ruminal degradability of soybean meal three times weekly were that intermittent supplementation supplemental protein influences the able to sustain elevated ruminal with a protein source greater in RUP efficiency of protein use and/or N ammonia concentrations compared may further improve efficiency of N recycling in the infrequently supplewith steers supplemented daily, utilization by ruminants. However, mented ruminant animal deserves thereby maintaining a desirable data are limited comparing the effects further investigation. digestion environment and improved of RDP vs RUP supplemented at ruminal N status, even on days when infrequent intervals on endogenous supplement was not provided. N recycling and efficiency of N use. Similarly, Krehbiel et al. (15) conBohnert et al. (4) noted that infreOscillating dietary protein concencluded that ewes fed low quality quent protein supplementation at up trations has no detrimental effect on
Implications
34
Ludden et al.
animal performance; thus, this feeding regimen can be used under practical feeding conditions and incorporated into supplementation programs with minimal impact on the performance of ruminant animals. Moreover, oscillating the protein concentration in the diet may provide producers with a management alternative that may ultimately decrease supplementation costs and improve economic returns. The mechanism(s) whereby ruminants are capable of maintaining performance under conditions of intermittent protein supplementation may be related to improvements in efficiency of protein utilization. Although such improvement is likely via enhanced recycling of endogenous nitrogen to the rumen, further research into the effects of intermittent protein supplementation on the dynamics of protein utilization in the ruminant is warranted.
Acknowledgments We gratefully acknowledge the assistance of Lane Ciminski, Dwayne Byerly, and the University of Wyoming Beef Farm for their assistance with feeding, animal care, and sample collection associated with this project. We also thank West Central Cooperative (Ralston, IA) for donation of the SoyPLUS® used in this project. This research was supported in part by the University of Wyoming Faculty Grant-In-Aid Program.
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