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Energy and protein requirements for growth and maintenance of F₁ Nellore x Red Angus bulls, steers, and heifers¹

M. L. Chizzotti^*,, S. C. Valadares Filho^*, L. O. Tedeschi^,2, F. H. M. Chizzotti^*, and G. E. Carstens

^* Department of Animal Science, Universidade Federal de Viçosa, Viçosa, MG 36571, Brazil; and Department of Animal Science, Texas A&M University, College Station, TX 77843-2471

	Abstract

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION IMPLICATIONS LITERATURE CITED

 
A comparative slaughter trial was conducted with 36 F₁ Nellore x Red Angus calves (12 steers, 12 bulls, and 12 heifers), averaging 274 kg of BW, to assess the net requirements of protein and energy for growth and maintenance. Three cattle from each group (i.e., steers, bulls, and heifers) were slaughtered at the beginning of the trial to determine the initial body composition. The remaining calves were randomly assigned to 1 of 3 treatments: maintenance (diet containing 70% of DM as corn silage fed at 1.2% of BW daily) or concentrate at 0.75 or 1.5% of BW daily with corn silage available for ad libitum consumption. The diets were isonitrogenous (2% N, DM basis). The experimental design provided ranges in ME intake, BW, and ADG for the development of regression equations to predict the maintenance requirements for NE and net protein (MRNE and MRNP, respectively) and the growth requirement for NE and net protein (GRNE and GRNP, respectively). After 84 d of growth, the cattle were slaughtered. The cleaned gastrointestinal tracts, organs, carcasses, heads, hides, tails, feet, blood, and tissues were weighed to measure empty BW (EBW). These parts were ground separately and subsampled for chemical analyses. For each animal within a period, DMI was measured daily and samples of feces were collected to determine diet digestibility. There were no differences in MRNE (P = 0.06) among groups. The combined data indicated a MRNE of 71.2 kcal·kg^–0.75 of EBW·d^–1, with a partial efficiency of use of ME to NE_m of 0.71. The partial efficiency of use of ME to NE for growth was 0.54 for bulls, 0.47 for steers, and 0.54 for heifers. The GRNE for steers and heifers were similar (P = 0.15) but were 18.7% greater (P = 0.03) for steers and heifers than for bulls. The MRNP did not differ among groups and averaged 2.53 g of CP·kg^–0.75 of EBW·d^–1. Likewise, GRNP was not different among groups. The percentage of retained energy deposited as protein (RE_p) increased as the content of retained energy in the gain (RE_c, Mcal/kg of empty body gain) decreased. The RE_p equation of the pooled data was 46.5 x e^{–0.2463 x RE_c}. We conclude that the energy requirement of crossbred Bos indicus x Bos taurus for maintenance might be less than that of purebred Bos taurus and that RE_p is nonlinearly, negatively correlated with RE_c. The GRNE was less for bulls than for steers and heifers. However, we found no differences in MRNE, MRNP, and GRNP for bulls, steers, and heifers of Nellore x Red Angus crossbreds.

Key Words: beef cattle • Bos indicus • comparative slaughter • digestible energy • net energy • net protein

	INTRODUCTION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION IMPLICATIONS LITERATURE CITED

 
The nutrient requirements recommended by NRC (2000) are widely adopted to formulate diets around the world. Nevertheless, the nutrient requirement equations were based on Bos taurus cattle, with adjustments to maintenance requirements for NE (MRNE) for Bos indicus breeds. Crossbred cattle (Bos indicus x Bos taurus) are an important component of beef production systems in several parts of the world, including tropical and subtropical regions. The availability and quality of meat depends on accurate information about energy and nutrient requirements for these breeding systems. According to the NRC (2000), Bos indicus breeds of cattle require about 10% less energy for maintenance than beef breeds of Bos taurus cattle, with crossbreds being intermediate. Nevertheless, Tedeschi et al. (2002), using data of 3 studies with Nellore (Bos indicus) steers and bulls, found maintenance requirements similar to those adopted by the NRC (2000) for Bos taurus breeds.

Additionally, it has been recognized that whether animals are castrates or intact males or females influences growth of body tissues, carcass composition, and efficiency of gain (Berg and Butterfield, 1976), and the energy and nutrient requirements for maintenance (ARC, 1980). The NRC (2000) also discussed the effect of sex on energy requirements for maintenance and growth, although few studies have compared groups under the same experimental conditions.

The objective of this study was to use body composition data from a comparative slaughter trial of bulls, steers, and heifers of Nellore (Bos indicus) and Red Angus (Bos taurus) crossbreds fed high levels of forage to determine the energy and protein requirements for maintenance and growth.

	MATERIALS AND METHODS

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Animal and Management Description

The trial was conducted at the Federal University of Viçosa, in Brazil, with 36 F₁ Nellore x Red Angus calves (12 bulls, 12 steers, and 12 heifers). Humane animal care and handling procedures were followed, according to the guidelines of the Federal University of Viçosa (Brazil).

All calves were from the same sire (Red Angus). The average age and initial shrunk BW (SBW) were 14 to 16 mo and 275 ± 7 kg for bulls, 14 to 16 mo and 278 ± 8 kg for steers, and 12 to 14 mo and 228 ± 10 kg for heifers. The cattle were fed the same diet during 2 wk (75% corn silage and 25% concentrate C1, DM basis; Table 1) until the beginning of the experiment. The average initial DMI was 2.36 ± 0.35% of BW daily. The diet DM was formulated to be isonitrogenous (2% N and 12.5% CP) among treatments and consisted of corn silage and concentrate (Table 1). The baseline cattle were composed of 3 randomly selected calves of each group (i.e., steers, bulls, and heifers). Three cattle of each group were randomly assigned to 3 treatments: fed at maintenance (1.2% of BW daily of a diet containing 70% corn silage and 30% concentrate C1, DM basis) or fed concentrate at 0.75 or 1.5% of BW daily with corn silage offered for ad libitum consumption. Calves fed at the maintenance level and at 0.75% of BW of concentrate daily received the concentrate C1, whereas calves fed at 1.5% of BW daily received the concentrate C2 (Table 1); concentrate C1 had greater content of CP and minerals than concentrate C2 to ensure a similar intake of these nutrients between cattle fed at 0.75 or 1.5% of BW of concentrate daily. The cattle were fed twice daily (at 0700 and 1600) in individual, sheltered pens. Feeds and orts were weighed daily, sampled, and frozen. There were 3 growing periods of 28 d, beginning after the slaughter of the baseline cattle. The cattle were weighed at the beginning and at the end of each period, during which animal performance and diet composition and digestibility were measured. A 14-d adaptation period was used to adapt cattle to the diets.

Digestion trials were conducted with all cattle in each period to determine diet DE. Indigestible ADF was used as a marker to estimate fecal DM excretion. Feces were collected at 0800 on d 15, at 1200 on d 17, and at 1600 on d 19 of each experimental period. The samples of feces, feeds (silage and concentrate), and orts of the week of the digestibility trial were dried at 60 to 65°C, ground to pass a 1-mm screen, and proportionally subsampled to a composite sample. The composite sample for each material (silage, concentrate, orts, and feces) was used to determine the ether extract (EE, by loss in weight of the dry sample upon extraction with diethyl ether in Soxhlet extraction apparatuses for 6 h; AOAC, 1990), protein (N analysis via microKjeldahl using 0.3 g of sample; AOAC, 1990), NDF (Van Soest et al., 1991), and ash (complete combustion in a muffle furnace at 600°C for 6 h; AOAC, 1990). Nonfiber carbohydrates (NFC) were calculated as 100 – [(%CP – %CP from urea + % of urea) + %NDF + %EE + %ash] (Hall, 2000), and apparent TDN was calculated as (CP intake – fecal CP) + (NDF intake –fecal NDF) + (NFC intake – fecal NFC) + [2.25 x (EE intake – fecal EE)] (Sniffen et al., 1992).

Urinary N Excretion

Because total urinary output was not obtained in this study, urinary creatinine concentration was used as an indicator of urine output (Chizzotti et al., 2007). Urine samples were collected from all cattle on d 14 of the second experimental period, 4 h after feeding. Urinary N contents were analyzed as described above, but using 2 mL of sample. Commercial kits were used to analyze these samples for creatinine (No. 555-A; Sigma Chem. Co., St. Louis, MO). Urine volume was estimated using creatinine concentration as a marker and assuming a daily creatinine excretion of 27.8 mg/kg of BW (Rennó, 2003). Urinary N excretion was calculated as N content multiplied by the estimated urine volume.

Slaughter and Body Composition Techniques

Before slaughter, SBW was measured as the BW after 18 h without feed and water. At slaughter, cattle were stunned using a Cash knocker (GIL, Ribeirão Preto, Brazil) and killed by exsanguination using conventional humane procedures. Blood was weighed and sampled. The body was separated into individual components, which were separately weighed. Included were internal organs (liver, heart, lungs, trachea, kidneys, reproductive tract, and spleen), cleaned digestive tract (rumen, reticulum, omasum, abomasum, and small and large intestines), tongue, tail, hide, head, feet, and carcass. The digestive tract was cleaned by emptying and flushing with water, and physically stripped. The carcass was split into 2 identical, longitudinal halves. After a 24-h chill, the whole, right half of the carcass was manually separated into bone, muscle, and fat. Head and feet were separated into bone, hide, and soft tissue. Internal organs, cleaned digestive tract, tail, and tongue were ground together. Muscle, fat, and soft tissues of head and feet were ground separately. Hide was sampled and cut into small pieces. Carcass, head, and feet bones were sawn into small pieces, homogenized, and proportionally sampled. Except for blood samples, which were dried at 60°C for 72 h, all other samples were dried at 105°C for 80 h for DM determination and partially defatted by washing with diethyl ether; the fat was computed by weight difference. Then, these samples were ground again in a ball mill (TE350, Tecnal, Piracicaba, Brazil) and analyzed for EE and N as described above.

Empty BW (EBW) was computed as the sum of the right and left halves of the warm carcass, hide, head, feet, tail, blood, cleaned gastrointestinal tract, and internal organs.

Data Calculation and Analyses

Prediction of Diet ME. The dietary DE was estimated as 4.409 Mcal/kg of TDN, and DE was converted to ME using an efficiency of 82% to convert DE to ME (NRC, 2000). The 82% is consistent with the findings of Tedeschi et al. (2002) using Nellore cattle and a similar diet.

Calculation of Initial Body Composition. The procedures used to compute energy retained and maintenance energy requirement were similar to those of Lofgreen and Garrett (1968). The initial EBW was computed from SBW, and then initial empty body fat (EBF) and empty body protein (EBP) were estimated from EBW for each animal, using the average EBW, SBW, EBF, and EBP data from the baseline cattle of the appropriate group.

Net Requirement Calculations. Empty body gains of body components were calculated as the difference between initial and final weights of the respective body components, similar to the methods of Tedeschi et al. (2002). The caloric values of retained fat and protein were assumed to be 9.367 and 5.686 Mcal/kg (Blaxter and Rook, 1953), respectively. Heat production (HP, kcal·kg^–0.75 of EBW·d^–1) was calculated as the difference between ME intake (MEI, kcal·kg^–0.75 of EBW·d^–1 and retained energy (RE, kcal·kg^–0.75 of EBW·d^–1). The average of the antilog of the intercept confidence interval (95%) of the linear regression between the log of HP on MEI was used to estimate the MRNE (kcal·kg^–0.75 of EBW·d^–1; Lofgreen and Garrett, 1968). The maintenance requirement for ME (MRME) was calculated by iteration, assuming that the maintenance requirement is the value at which HP is equal to MEI (kcal·kg^–0.75 of EBW·d^–1). The efficiency of energy utilization for maintenance (K_m) was calculated as MRNE/MRME. The slope of the regression of RE on MEI was assumed to be the efficiency of energy utilization for growth (K_g). Alternatively, we used the intercept divided by K_g to compute MRME, which was then multiplied by K_m to estimate MRNE. This second approach of calculating MRNE was compared with the MRNE estimated using the regression of the log of HP on MEI.

The maintenance requirement for net protein (MRNP, g·kg^–0.75 of EBW·d^–1) was calculated as 6.25 times the negative intercept of the linear regression of the N balance calculated by difference (N intake minus N excreted in feces and urine, g·kg^–0.75 of EBW·d^–1) on N intake (g·kg^–0.75 of EBW·d^–1; INRA, 1988). Alternatively, the MRNP was calculated as 6.25 times the negative intercept of the linear regression of the retained N calculated from tissue deposition (g·kg^–0.75 of EBW·d^–1) on N intake (g·kg^–0.75 of EBW·d^–1).

The growth requirement for NE (GRNE, Mcal·kg^–0.75 of EBW·d^–1) was calculated as shown in Eq. [1], and the growth requirement for net protein (GRNP, g·kg^–0.75 of EBW·d^–1) was calculated as shown in Eq. [2]:

[1]

[2]

where a is the antilog of the intercept and b is the slope of the linear regression of the logarithm of RE (Mcal·kg^–0.75 of EBW·d^–1) on the logarithm of empty body gain (EBG, kg/d), and w is the antilog of the intercept and z is the slope of the linear regression of the logarithm of body protein (kg/kg of EBW) on the logarithm of EBW.

Statistical Analyses.

Statistical analyses were performed using SAS (SAS Inst. Inc., Cary, NC). The analyses of intake, diet energetic concentration, performance, and body composition were performed with PROC GLM, using a 3 x 3 factorial design of diet (maintenance level or 0.75 or 1.5% of BW as concentrate daily) and group (bulls, steers, and heifers), as per the following statistical model:

where µ is the mean, is the effect of diet, ß is the effect of group, ß is the interaction of diet and group, and is the random error.

Outliers and systematic bias were identified using the plot of Studentized residuals against the predicted values (X-variable) and by the leverage and Cook’s D coefficients (Neter et al., 1996). At the end of the experiment, during the cleaning of a pen, 1 heifer was injured and, therefore, was removed from the data set.

The comparison of intercept and slope among diets and group was performed using PROC GLM with the SOLUTION statement and the sum of squares type 3. The interaction or the main effects were removed from the statistical model if, and only if, P > 0.05. The comparisons of means were performed using least squares means at P = 0.05.

	RESULTS AND DISCUSSION

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Intake and Digestibility

Table 2 shows the mean intake and digestibility of the nutrients. There were effects of group and diet on intake of all nutrients (kg/d). As expected, cattle fed at maintenance level had the lowest intake of all nutrients and the greatest diet DE concentration. Digestibility in the rumen is the result of the competition between digestion and passage rates, and passage rate is positively correlated with DMI (Van Soest, 1994). Therefore, the lesser DMI of cattle on restricted intake likely resulted in a slower passage rate and a greater digestibility of the diet. Cattle fed at 0.75% of BW of concentrate daily had less (P = 0.01) DMI than cattle fed at 1.5% of BW as concentrate daily because their diets had a greater forage to concentrate ratio, which might have decreased the ruminal escape of DM and limited the intake by rumen filling effect (Allen, 1996). Bulls had the greatest DMI (kg/d), but there were no differences (P = 0.85) among groups on DMI as a percentage of BW. Bulls had greater intakes (P = 0.04) of NFC than steers, but they had similar (P = 0.95) energy intake. Heifers had less intake than bulls and steers, probably due to their lighter mean BW.

Table 3 shows the mean body composition for the baseline cattle of each group. The initial SBW and mean body composition was similar between bulls and steers, but heifers had lighter SBW and greater fat (% of EBW) than males, likely because the heifers were closer to their mature weight.

Group had no effect on RE and HP (kcal·kg^–0.75 of EBW·d^–1), but RE and HP increased as cattle consumed more energy, indicating that HP increased as MEI increased. Turner and Taylor (1983) suggested that HP is greater in cattle with increased plane of nutrition mainly due to elevation of metabolism involved in the synthesis of RE. Similarly, Williams and Jenkins (2003) proposed that ME consumed above the maintenance requirement is associated with an elevation of vital functions (support metabolism) and that this HP is driven by amount of MEI.

The intercept and the slope of the regression of log of the HP on MEI as well as MRNE are shown in Table 5. The exponential relationship between HP and MEI are shown in Figure 1. There were no differences (P = 0.06) in MRNE among groups; steers had a 9 and 13% lower MRNE than bulls and heifers, respectively. The analysis of the pooled data resulted in a common MRNE of 71.2 kcal·kg^–0.75 of EBW·d^–1, which is 7% less than the MRNE of 77 kcal·kg^–0.75 of EBW·d^–1 reported by Lofgreen and Garrett (1968), and corroborates the assumption of the NRC (2000) that Bos indicus crossbreds have lower MRNE requirements. Our value is nearly identical to the value of 70.8 kcal·kg^–0.75 of EBW·d^–1 reported by Silva et al. (2002) in a data compilation of F1 Bos indicus x Bos taurus bulls. The average value of MRNE reported by Ferrell and Jenkins (1998) for steers of Bos indicus crossbreds was 74.5 kcal·kg^–0.75 of EBW·d^–1. Henrique et al. (2005) using data of 320 Nellore purebred and crossbred cattle obtained from 8 comparative slaughter studies reported a MRNE of 73 kcal·kg^–0.75 of EBW·d^–1. Paulino et al. (2006) using individual observations collected from 7 different trials composed of 135 intact Nellore males that averaged 303 kg also found a MRNE of 73 kcal·kg^–0.75 of EBW·d^–1. The lower MRNE for Nellore crossbreds could be attributed to the lower ratio of kidney-pelvic-renal fat to carcass fat, lower internal organs mass, and lower protein turnover of B. indicus compared with B. taurus cattle (Valadares Filho et al., 2005). In contrast, the MRNE reported by Ferrell and Jenkins (1998) for Brahman crossbreds was 82.8, which is 16% greater than our finding, but this divergence could be attributed to differences in environmental conditions. Tedeschi et al. (2002) also reported a greater MRNE of 77.2 kcal·kg^–0.75 of EBW·d^–1 for Nellore purebred cattle (348 kg of BW), but they also did not find differences between bulls (69.8) and steers (81.2) in MRNE.

View larger version (8K): [in this window] [in a new window]   Figure 1. Exponential relationship between heat production (HP) and ME intake (MEI) for all cattle (HP = 71.3 x e(0.0034 x MEI), R2 = 0.95). Data are from bulls (), steers (), and heifers (x).

The mean values of intake, excretion, balance, and retention of N are presented in Table 7. The intake, excretion, and balance of N (g·kg^–0.75 of EBW·d^–1) were not different among groups (P = 0.06, 0.15, and 0.56, respectively); however, as expected, they were affected by diet in that cattle in the maintenance treatment had lesser values than cattle fed concentrate at 0.75 or 1.5% of BW daily. There was an interaction between group and diet for retained N; cattle in the maintenance treatment had the smallest value, and bulls and heifers of treatments 0.75 and 1.5% of BW as concentrate daily retained more N (g·kg^–0.75 of EBW·d^–1) than steers (0.41 and 0.53, 0.41 and 0.43, and 0.24 and 0.40, respectively). Daily N balance and retained N (g of N·kg^–0.75 of EBW·d^–1) were regressed against daily N intake (g of N·kg^–0.75 of EBW·d^–1) to determine MRNP (Figure 2). The MRNP is assumed to be the sum of endogenous urinary N, metabolic fecal N, and dermal (scurf and hair) N losses, multiplied by the factor 6.25 (NRC, 1985). When N balance is regressed against N intake, the negative intercept (at zero N intake) provides an estimate of minimum N losses, which should be similar to the sum of endogenous urinary N and metabolic fecal N (Susmel et al., 1993). There were no differences (P = 0.45) in MRNP among groups. The pooled data indicated a MRNP of 0.40 g of N·kg^–0.75 of EBW·d^–1, which is equivalent to 2.53 g of CP·kg^–0.75 of EBW·d^–1. The efficiency of conversion of maintenance requirement for MP (MRMP) to MRNP of feeding systems ranges from 0.67 for NRC (1985) to 1.0 for ARC (1980). Assuming an efficiency of 0.67, the calculated MRMP was 3.78 g of CP·kg^–0.75 of EBW·d^–1, which is equivalent to 3.4 g of CP·kg^–0.75 of SBW·d^–1. This value was 10% lower than the recommendation of NRC (2000) of 3.8 g of CP·kg^–0.75 of EBW·d^–1. The Institute National de la Recherche Agronomique (INRA, 1988) used N balance studies to determine the maintenance requirement of 3.25 g of MP·kg^–0.75 of SBW·d^–1. Similarly, Smuts (1935) determined a value of 3.52 g of MP·kg^–0.75 of SBW·d^–1, which was close to our findings. Even though our MRMP value was similar to those values reported in the literature, the diets in our experiments were designed to be first limiting in energy, whereas protein is first limiting in experiments designed to determine protein requirements using the regression of N balance on N intake.

View larger version (11K): [in this window] [in a new window]   Figure 2. Relationships between N balance, retained N, and N intake (g·kg–0.75 of empty BW·d–1). Symbols are data from bulls ( and ), steers ( and •), and heifers ( and ). Open symbols and dashed line are from N balance calculated by the difference of N ingested minus excreted N {N balance = –0.405 (± 0.050) + [0.355 (± 0.026) x N intake], r2 = 0.91} and filled symbols and solid line are from retained N calculated from tissue deposition {retained N = –0.495 (±0.058) + [0.406 (± 0.030) x N intake], r2 = 0.85}.

Energy Requirement for Growth

Table 8 depicts the intercept and slope of the regression equations of logarithm of body fat, energy, and protein content on the logarithm of the EBW. As cattle grow the content of energy and fat increases, whereas the content of protein decreases in the EBG (Berg and Butterfield, 1976). There were differences (Table 8) on the rate of fat deposition in which the percentage of fat in the EBG was greater (P = 0.03), on a decreasing order, in steers, heifers, and then bulls, for cattle weighing more than 360 kg.

View larger version (7K): [in this window] [in a new window]   Figure 3. Relationship between logarithms of retained energy (RE) and empty body gain (EBG) for bulls [log RE = –1.317 + (1.059 x log EBG), solid line] and steers and heifers [log RE = –1.227 + (1.065 x log EBG), dashed line]. Data are from bulls (), steers (), and heifers (x).

The protein deposition in the empty body has been estimated using the rate of ADG and the composition of the gain (NRC, 2000). The composition of the gain depends on physiological maturity of the cattle, which is affected by group and breed (NRC, 1984). Although not significantly different among groups (Table 8), steers had GRNP that were 14 and 17% less than those of bulls and heifers, respectively. This tendency is in contrast with the findings reported by Robelin and Daenicke (1980), who evaluated the effect of sex on body composition and found the percentage of protein in the EBG of steers and heifers was 10% less than in bulls. Our finding was because cattle had similar BW, but different body chemical composition, likely due to different degrees of maturity, which would affect the composition of the gain and the requirements for protein (Owens et al., 1995).

The percentage of RE deposited as protein (RE_p) increased as content of RE in the gain (RE_c, Mcal/kg of EBG) decreased (Figure 4), suggesting that RE_p can be used to compute the partial efficiency of ME to NE for growth (Williams and Jenkins, 2003; Tedeschi et al., 2004). No differences (P = 0.81) among groups occurred; the RE_p equation of the pooled data was 46.5 x e^{–0.2463 x RE_c} (R²= 0.67). Geay (1984) found that RE_p was greater for bulls than for heifers and decreased as the RE increased; however, Tedeschi et al. (2002) did not detect differences between bulls and steers. The equation developed by Tedeschi et al. (2004) for Nellore bulls and steers overpredicts the RE_p, likely due to the greater fat content and consequent lesser protein content of the EBG of Nellore x Red Angus crossbreds. This finding is in agreement with the discussion above, regarding the possible differences in maturity degree of our cattle compared with other studies.

View larger version (6K): [in this window] [in a new window]   Figure 4. Relationship between the percentage of retained energy deposited as protein (%REp) and the content of retained energy in the empty body gain (REc; Mcal/kg of empty body gain, EBG): %REp = 46.5 x e–0.2463 xREc, R2 = 0.67). Data are from bulls (), steers (), and heifers (x). Solid line is from data of this trial, and dashed line is the equation proposed by Tedeschi et al. (2004; %REp = 5.54 + 169.39 x e– 0.5573 xREc).

	IMPLICATIONS

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	Footnotes

 
¹ We thank the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Brazil) and Fundação de Amparo a Pesquisa de Minas Gerais (FAPEMIG, Brazil) for providing the financial support.

² Corresponding author: luis.tedeschi{at}tamu.edu

Received for publication September 15, 2006. Accepted for publication April 18, 2007.

	LITERATURE CITED

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Allen, M. S. 1996. Physical constraints on voluntary intake of forages by ruminants. J. Anim. Sci. 74:3063–3075.[Abstract]

AOAC. 1990. Official Methods of Analysis. 15th ed. Assoc. Offic. Anal. Chem., Arlington, VA.

ARC. 1980. The Nutrient Requirements of Ruminant Livestock. Technical Review. Commonw. Agric. Bureaux, Farnham Royal, UK.

Berg, R. T., and R. M. Butterfield. 1976. New Concepts of Cattle Growth. Macarthur Press, Sydney, Australia.

Blaxter, K. L., and A. J. F. Rook. 1953. The heat of combustion of the tissues of cattle in relation to their chemical composition. Br. J. Nutr. 7:83–91.[CrossRef][Medline]

Chizzotti, M. L., S. C. Valadares Filho, R. F. D. Valadares, F. H. M. Chizzotti, and L. O. Tedeschi. 2007. Determination of creatinine excretion and evaluation of spot urine sampling in Holstein cattle. Livest. Sci. doi:10.1016/j.livsci.2087.03.013.

Ferrell, C. L., and T. G. Jenkins. 1998. Body composition and energy utilization by steers of diverse genotypes fed a high-concentrate diet during the finishing period: II. Angus, Boran, Brahman, Hereford, and Tuli sires. J. Anim. Sci. 76:647–657.[Abstract/Free Full Text]

Geay, Y. 1984. Energy and protein utilization in growing cattle. J. Anim. Sci. 58:766–778.[Abstract/Free Full Text]

Hall, M. B. 2000. Calculation of non-structural carbohydrate content of feeds that contain non-protein nitrogen. Bulletin 339:A-25. Univ. Florida, Gainesville.

Henrique, D. S., R. A. M. Vieira, P. A. M. Malafaia, M. C. Mancini, and A. L. Gonçalves. 2005. Estimation of the total efficiency of metabolizable energy utilization for maintenance and growth by cattle in tropical conditions. R. Bras. Zootec. 34:1006–1016.

INRA. 1988. Alimentation des Bovins, Ovins, et Caprins. R. Jarrige, ed. Institut National de la Recherche Agronomique, Paris, France.

Lofgreen, G. P., and W. N. Garrett. 1968. A system for expressing net energy requirements and feed values for growing and finishing beef cattle. J. Anim. Sci. 27:793–806.[Abstract/Free Full Text]

Neter, J., M. H. Kutner, C. J. Nachtsheim, and W. Wasserman. 1996. Applied Linear Statistical Models. 4th ed. McGraw-Hill, New York. NY.

NRC. 1984. Nutrient Requirements of Beef Cattle. 6th ed. Natl. Acad. Press, Washington, DC.

NRC. 1985. Ruminant Nitrogen Usage. Natl. Acad. Press, Washington, DC.

NRC. 2000. Nutrient Requirements of Beef Cattle. Updated 7th ed. Natl. Acad. Press, Washington, DC.

Owens, F. N., D. R. Gill, D. S. Secrist, and S. W. Coleman. 1995. Review of some aspects of growth and development of feedlot cattle. J. Anim. Sci. 73:3152–3172.[Abstract]

Paulino, P. V. R., S. C. Valadares Filho, M. A. Fonseca, K. A. Magalhães, E. Detmann, and R. D. Sainz. 2006. Maintenance energy requirements of Nellore bulls in Brazil. J. Anim. Sci. 84(Suppl. 1):223–224. (Abstr.)

Rennó, L. N. 2003. Intake, total and partial digestibility, microbial production, ruminal parameters and excretions of urea and creatinine by steers fed diets containing four urea levels or two protein levels. PhD Diss. Universidade Federal de Viçosa, MG, Brazil.

Robelin, J., and R. Daenicke. 1980. Variations of net requirements for cattle growth with liveweight, liveweight gain, breed and sex. Annales de Zootechnie 29:99–118.

Silva, F. F., S. C. Valadares Filho, L. C. V. Ítavo, C. M. Veloso, R. F. D. Valadares, P. R. Cecon, P. V. R. Paulino, and E. H. B. K. Moraes. 2002. Net and dietary energy, protein and macrominerals requirements of beef cattle in Brazil. R. Bras. Zootec. 31:776–792.

Smuts, D. B. 1935. The relation between the basal metabolism and the endogenous nitrogen metabolism, with particular reference to the estimation of the maintenance requirement of protein. J. Nutr. 9:403–433.[Free Full Text]

Sniffen, C. J., J. D. O’Connor, P. J. Van Soest, D. G. Fox, and J. B. Russell. 1992. A net carbohydrate and protein system for evaluating cattle diets: II. Carbohydrate and protein availability. J. Anim. Sci. 70:3562–3577.[Abstract]

Susmel, P., M. Spanghero, B. Stefano, C. R. Mills, and E. Plazzotta. 1993. Digestibility and allantoin excretion in cows fed diets differing in nitrogen content. Livest. Prod. Sci. 36:213–222.[CrossRef]

Tedeschi, L. O., C. Boin, D. G. Fox, P. R. Leme, G. F. Alleoni, and D. P. D. Lanna. 2002. Energy requirement for maintenance and growth of Nellore bulls and steers fed high-forage diets. J. Anim. Sci. 80:1671–1682.[Abstract/Free Full Text]

Tedeschi, L. O., D. G. Fox, and P. J. Guiroy. 2004. A decision support system to improve individual cattle management. 1. A mechanistic, dynamic model for animal growth. Agric. Systems 79:171–204.[CrossRef]

Turner, H. G., and C. S. Taylor. 1983. Dynamic factors in models of energy utilization with particular reference to maintenance requirement of cattle. World Rev. Nutr. Diet 42:135–190.[Medline]

Valadares Filho, S. C., P. V. R. Paulino, and R. D. Sainz. 2005. Desafios metodológicos para determinação das exigências nutricionais de bovinos de corte no Brasil. Pages 261–287 in Proc. 42nd Annu. Meet. Brazilian Soc. Anim. Sci. Brazilian Soc. Anim. Sci., Goiânia, GO, Brazil.

Van Soest, P. J. 1994. Nutritional Ecology of the Ruminant, 2nd ed. Cornell Univ. Press, Ithaca, NY.

Van Soest, P. J., J. B. Robertson, and B. A. Lewis. 1991. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74:3583–3590.[Abstract]

Williams, C. B., and T. G. Jenkins. 2003. A dynamic model of metabolizable energy utilization in growing and mature cattle. III. Model evaluation. J. Anim. Sci. 81:1390–1398.[Abstract/Free Full Text]

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