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Journal of Animal Science - Animal Nutrition

Intake, digestibility, performance, and nitrogen metabolism of feedlot-finished young bulls (Bos indicus) fed diets containing peanut cake1


This article in JAS

  1. Vol. 94 No. 11, p. 4720-4727
    Received: Dec 04, 2015
    Accepted: Sept 08, 2018
    Published: October 27, 2016

    2 Corresponding author(s):

  1. B. R. Correia 2*,
  2. G. G. P. de Carvalho,
  3. R. L. Oliveira,
  4. A. J. V. Pires,
  5. O. L. Ribeiro*,
  6. R. R. Silva,
  7. A. G. Leão§ and
  8. P. A. Oliveira
  1. * Department of Animal Science, Federal University of Recôncavo Bahia, Rua Rui Barbosa, 710, Centro, 44380000, Cruz das Almas, Bahia, Brazil
     Department of Animal Science, Federal University of Bahia, Av. Adhemar de Barros, 500, Ondina, 40170110, Salvador, Bahia, Brazil
     Department of Animal Science, State University of Southwest Bahia, Praça Primavera, 40, Primavera, 45700000, Itapetinga, Bahia, Brazil
    § Department of Animal Science, Federal University of Mato Grosso, Av. Fernando Corrêa da Costa, 2367, Boa Esperança, 78060900, Cuiabá, Mato Grosso, Brazil


This aim of this study was to evaluate the use of peanut cake as a dietary substitute for soybean meal and to determine the effects on intake, apparent digestibility, performance, and N metabolism in feedlot-finished young bulls. Thirty-two young Nellore bulls with an average initial BW of 390 ± 43.5 kg were distributed in a completely randomized design and individually housed in stalls. The young bulls were fed Tifton 85 hay and 4 concentrate mixes containing 0, 33, 66, or 100% peanut cake replacing soybean meal. The diets were formulated to be isonitrogenous, containing 150 g/kg CP, and isocaloric (65% TDN), to have a 40:60 forage:concentrate ratio, and were provided as a total mixed ration. The experiment lasted 90 d and data were collected every 28 d. Blood and urine samples were taken during the last 6 d. Intakes of DM (P = 0.005), OM (P = 0.006), CP (P = 0.002), NDF (P = 0.022), nonfiber carbohydrates (P = 0.002), and TDN (P = 0.018) linearly decreased as the dietary inclusion of peanut cake in the diet was increased. Conversely, intake and ether extract digestibility linearly increased (P < 0.035). The average daily weight gain decreased (P = 0.015) as the peanut cake levels were increased. Plasma urea N decreased (linearly; P = 0.005). Peanut cake may not be used to replace soybean meal in the diet of young feedlot-finished Nellore bulls.


One challenge in raising feedlot-finished young bulls is to reduce animal feed costs with diet adaptation and rational use of natural resources. Soybean meal is the best and most commonly used N source for ruminants (Correia et al., 2016). However, studies regarding protein sources from biodiesel production have been conducted to evaluate the chemical composition of these alternative feeds on metabolic responses of the animals fed these diets (Correia et al., 2011; Silva et al., 2015; de Oliveira et al., 2016).

In Brazil, governmental incentives for biodiesel production have resulted in production of oleaginous cakes from oil extraction. One of these byproducts, peanut cake, warrants investigation due to its similar chemical composition to soybean meal (Abdalla et al., 2008; Pereira et al., 2016). Peanut cake contains a high protein content, an important nutrient for maintenance and production performance in cattle, which potentially can be used in ruminant diets (Correia et al., 2011). According to Silva et al. (2015), this byproduct may represent an eventual alternative for use in diets for goat kids.

Correia et al. (2015) found that the replacement of soybean meal with peanut cake in diets for feedlot cattle did not affect the feeding behavior of the animals. We hypothesized that the peanut cake can completely replace soybean meal in diets for young feedlot-finished bulls. To test this hypothesis, we evaluated the effect of replacing soybean meal with peanut cake on intake, digestibility, performance, and N metabolism of young bulls.


This study was performed in strict accordance with the recommendations in the Guide for the National Council for Animal Experiments Control (CONCEA). The protocol was approved by the Committee in the Ethics of Animal Experiments of the Federal University of Bahia, Bahia State, Brazil (permit number 03-2012).

The experiment was performed between November 2010 and March 2011 at the Experimental Farm of the School of Veterinary Medicine and Animal Science of the Federal University of Bahia, which is located in the Mercês District, municipality São Gonçalo dos Campos (Bahia), Brazil, 12°23′57.51″ S and 38°52′44.66″ W.

Experimental Animals and Diets

Thirty-two young Nellore bulls with an initial BW of 390 ± 43.5 kg were distributed in a completely randomized experimental design with 4 treatments (n = 8). The animals were kept in individual 2.0 by 4.0 m partially covered stalls with feeders and drinkers. The experiment lasted 110 d, 20 d for adaptation and 90 d feedlot period.

The diets were formulated to be isonitrogenous (15% CP) and isocaloric (65% TDN), with a 40:60 forage:concentrate ratio total mixed ration. The diets were provided as a complete mixed diet as recommended by the NRC (1996) to promote daily weight gains of 1.2 kg. The feed consisted of peanut cake, soybean meal, ground corn, mineral premix, urea, ammonium sulfate, and Tifton 85 hay (Table 1). In each treatment, the soybean meal in the concentrated feed was replaced with peanut cake at 0, 33, 66, or 100% (Table 2).

View Full Table | Close Full ViewTable 1.

Chemical composition of ingredients used in the experimental diets

Item Ground corn Soybean meal Peanut cake Tifton 85 hay
DM, % 94.43 95.76 96.46 85.70
OM, g/kg DM 986.40 920.95 947.60 927.00
CP, g/kg DM 71.00 449.10 445.20 69.60
EE,1 g/kg DM 26.50 20.60 147.10 13.10
NDF,2 g/kg DM 118.40 259.10 176.00 803.50
ADF, g/kg DM 43.90 200.10 155.50 550.90
Lignin, g/kg DM 0.80 2.20 68.50 99.00
Nonfiber carbohydrates, g/kg DM 770.40 200.70 179.10 40.80
NDIN, g/kg CP 17.10 50.00 26.80 7.60
ADIN, g/kg CP 28.50 27.20 19.90 4.10
Estimated TDN,3 g/kg DM 865.00 722.50 782.20 536.50
1EE = ether extract .
2Corrected for ash and protein.
3Total digestible nutrients estimated by the equations described by Detmann et al. (2006a,b,c, 2007).

View Full Table | Close Full ViewTable 2.

Proportions of ingredient and chemical composition of experimental diets with peanut cake replacing soybean meal in diets for feedlot-finished young bulls

Rate of substitution of soybeanmeal for peanut cake, %
Item, % 0 33 66 100
Peanut cake 0.00 4.08 8.16 12.23
Soybean meal 12.16 8.10 4.05 0.00
Ground corn 44.88 44.91 44.94 44.91
Premix mineral1 1.52 1.48 1.43 1.43
Urea A/S2 1.43 1.43 1.43 1.43
Tifton 85 hay 40.00 40.00 40.00 40.00
Chemical composition
DM 91.27 91.29 91.32 91.35
Ash 4.39 4.32 4.25 4.18
CP 15.70 15.56 15.42 15.42
EE3 1.96 2.48 3.00 3.51
Total carbohydrates 77.94 77.64 77.33 76.89
NDF4 40.61 40.28 39.95 39.61
ADF 26.44 26.26 26.09 25.91
Nonfiber carbohydrates 38.65 38.59 38.52 38.42
Estimated TDN5 69.07 69.35 69.64 69.88
1Guaranteed values (per kg in active elements): 240.00 g calcium, 174.00 g phosphorous, 1,250.00 mg copper 100.00 mg cobalt, 1,795.00 mg iron, 90.00 mg iodine, 2,000.00 mg manganese, 15.00 mg selenium, 5,270.00 mg zinc, and maximum 1,740.00 mg fluoride.
2Urea and ammonium sulfate at a 9:1 ratio.]
3EE = ether extract.
4Corrected for ash and protein.
5Total digestible nutrients estimated by the equations described by Detmann et al. (2006a,b,c, 2007).

Intake and Digestibility

The young bulls were fed twice daily (0800 and 1600 h). For each experimental diet, the amount of feed and orts were weighed daily to estimate individual intake. The animals were fed according to the DMI of the previous day, and the diet was adjusted to allow orts equivalent to 10% of the diets supplied to avoid intake restriction.

Orts in the troughs were weighed daily and sampled 3 times per week to estimate intake and feed conversion. Samples of concentrate ingredients, hay, and orts were collected and stored at −20°C for subsequent chemical analysis.

Samples of feed and orts were dried at 55°C for 72 h and then ground in a Wiley knife mill (Tecnal Equipamentos Científicos, Piracicaba, São Paulo, Brazil) with a 1-mm sieve before being stored in carefully sealed plastic containers for laboratory analysis.

Analysis of the chemical composition of the feed ingredients samples was performed to determine the composition of DM (method 967.03; AOAC, 1990), ash (method 942.05; AOAC, 1990), CP (method 981.10; AOAC, 1990), and ether extract (EE; method 920.29; AOAC, 1990).

For analysis of NDF, samples were treated with thermostable α-amylase without the use of sodium sulfite and corrected for the residual ash content (Mertens, 2002). The correction of NDF and ADF for the N compounds and estimation of NDIN and ADIN were performed according to Licitra et al. (1996). The determination of the ADF was obtained by following the method of Van Soest et al. (1991). Lignin was determined according to method 973.18 (AOAC, 2002), in which the ADF residue was treated with 72% sulfuric acid. Total carbohydrates and percentage of nonfiber carbohydrates (NFC) were estimated as described by Sniffen et al. (1992). Total digestible nutrients was obtained from the following equation:in which DCP is the digestible CP, DEE is the digestible EE, DNDFap is the digestible NDF (free from ash and protein), and DNFC is digestible NFC.

In Tables 1 and 2, TDN was estimated using the following equation:in which the apparently digestible NFC (NFCad; %) was estimated using the following equation (Detmann et al., 2006b):for finishing cattle, in which Nonfiber carbohydrates corrected for ash and protein (NFCcp, %) is. The apparently digestible apparent EE (EEad; %) was estimated by the following equation (Detmann et al., 2006c):for finishing cattle, in which EE is expressed as a percent. The apparently digestible CP (CPad; %) was estimated by the following equation (Detmann et al., 2006a):for finishing cattle, in which CP is expressed as a percent. The NDF content corrected for ash and effectively digestible proteins (NDFd; %) for lactating cows was estimated according to Detmann et al. (2007) as follows:in which NDF corrected for ash and protein (NDFcp) is and Lig is Lignin, g/kg DM.

To evaluate the apparent digestibility of the nutritional components, animal feces were collected for 2 consecutive days at 12 and 17 h every 29 d during the experiment. Fecal samples from each animal were first dried and ground in a knife mill with a 1.0- and 2.0-mm mesh sieve before being stored for later analysis. Fecal excretion was estimated using indigestible NDF as an internal marker. Samples of the feed provided (Tifton 85 hay, soybean meal, peanut cake, and corn), orts, and feces (to obtain indigestible NDF) were incubated for 288 h (Detmann et al., 2012; method INCT-CA F-008/1) in the rumen of a young Holstein–Zebu crossbred bull fed with a mixed diet.


Animals were weighed at the beginning and end of the experiment, after being fasted for 12 h, and every 28 d during the performance trial, without fasting. Based on the collected data, ADG was calculated by dividing the individual weight gain by the time in feedlot, and feed conversion was determined as the ratio between DMI and ADG.

Nitrogen Metabolism

On the 87th day of confinement, spot urine samples were taken during spontaneous animal urination approximately 4 h after the morning feeding. The samples were filtered through cheesecloth, and a 10-mL aliquot was taken, diluted with 40 mL of sulfuric acid (0.036 N; Valadares et al., 1999), and reserved for quantification of the following concentrations in the urine: urea, N, creatinine, allantoin, and uric acid. The daily urine volume was estimated as the ratio of the daily excretion of creatinine found in the experiment divided by its concentration in the spot sample (mg/kg BW). The urine was analyzed to determine N levels using the Kjeldahl method (Detmann et al., 2012; method INCT-CA N-001/1), and purine derivatives (allantoin and uric acid) were measured according to Chen and Gomes (1992).

On the eighth day, 10 mL of blood was taken from the jugular vein approximately 4 h after the morning feeding using nonheparinized Vacutainer tubes (Becton, Dickinson and Co., São Paulo, São Paulo, Brazil). The samples were immediately sent to the laboratory, where they were centrifuged to separate the serum; the serum urea concentrations were obtained with a spectrophotometer using the protocol of the commercial enzymatic kit (Labtest Diagnóstica S.A., Lagoa Santa, Minas Gerais, Brazil). The concentration of urea N was calculated assuming 46% N in the urea.

Statistical Analysis

A general linear model was used to perform a linear regression using the PROC GLM from SAS (SAS Inst. Inc., Cary, NC). To determine the relationship between the rate of substitution and each evaluated parameter and to find the best rate of peanut cake for the substitution of soybean meal, a polynomial contrast was used to determine the linear and quadratic effects of treatments. The initial weight was used in the statistical model as a covariate when significant. Significance was declared when P < 0.05.


The decreased DM intake (P = 0.005) may have been caused by the increased EE levels when soybean meal was replaced with peanut cake in the diet (Table 2). This replacement increased the energy density of the diets due to the higher energy content of the peanut cake. Mertens (1994) reported that intake becomes limited by the physiological energy demand when high-energy diets are supplied and the fiber content is low.

Decreased DM intake due to increased lipid intake may be caused by physiological satiety mechanisms, which are not linked to reduced ruminal fiber degradation (Choi and Palmquist, 1996; Allen, 2000). The physiological mechanisms underlying this phenomenon are related to increased fatty acid oxidation in the liver and increased cholecystokinin secretion from endocrine cells that are concentrated in the proximal small intestine, which, via the vagus nerve reflex, stimulates the satiety center (Allen, 2000; Leonhardt and Langhans, 2004).

The linear decrease in CP intake (P = 0.002) observed in this study may be attributed to the reduced DM intake because the diets were formulated to be isonitrogenous (Table 3). Ether extract intake linearly increased (P = 0.003) with increasing dietary peanut cake levels; this increase was most likely attributable to the higher EE concentrations in the peanut cake. The dietary EE values were 1.96, 2.48, 3.00, and 3.55% for the 0, 33, 66, and 100% substitutions, respectively. However, these EE levels are below the maximum limits (between 5 and 7% EE in the DM) for ruminant diets (Vasconcelos and Galyean, 2007).

View Full Table | Close Full ViewTable 3.

Nutrient intake of feedlot diets with peanut cake replacing soybean meal in diets for feedlot-finished young bulls

Rate of substitution of soybean meal for peanut cake, %
Item 0 33 66 100 SEM Lin1 Quad2
DM, kg/d 10.58 9.67 9.15 8.05 0.245 0.005 0.483
DM, % BW 2.21 2.17 2.06 1.84 0.043 0.004 0.320
DM, g kg BW0.75 102.04 99.71 94.71 84.47 2.085 0.004 0.358
OM, kg/d 9.65 9.28 8.79 7.74 0.235 0.006 0.477
CP, kg/d 1.63 1.48 1.45 1.16 0.047 0.002 0.424
EE,3 kg/d 0.20 0.24 0.28 0.27 0.009 0.003 0.078
NDF,4 kg/d 3.78 3.76 3.34 3.21 0.097 0.022 0.825
NDF,4 % BW 0.83 0.84 0.75 0.74 0.016 0.019 0.699
NDF,4 g kg BW0.75 38.24 38.78 34.56 33.76 0.793 0.019 0.734
NFC,5 kg/d 4.20 3.93 3.83 3.21 0.104 0.002 0.382
TDN, kg/d 6.05 6.11 5.64 5.12 0.145 0.018 0.349
Regression equation
DM, kg/d Ŷ = 10.2037 − 0.0196325X r = 0.94
DM, % BW Ŷ = 2.25003 − 0.00356283X r = 0.91
DM, g/kg BW0.75 Ŷ = 103.792 − 0.173060X r = 0.92
OM, kg/d Ŷ = 9.79399 − 0.0186587X r = 0.94
CP, kg/d Ŷ = 1.64535 − 0.0042809X r = 0.90
EE, kg/d Ŷ = 0.212539 + 0.000737331X r = 0.73
NDF, kg/d Ŷ = 3.82979 − 0.00625205X r = 0.90
NDF, % BW Ŷ = 0.842726 − 0.00105747X r = 0.86
NDF, g/kg BW0.75 Ŷ = 38.8949 − 0.0524384X r = 0.87
NFC, kg/d Ŷ = 4.25576 − 0.00927779X r = 0.90
TDN, kg/d Ŷ = 6.2092 − 0.00972647X r = 0.86
1Linear effect.
2Quadratic effect.
3EE = ether extract.
4Value corrected for ash and protein.
5NFC = nonfiber carbohydrates.

The intakes of OM, NDF, NFC, and TDN followed the linear decrease in DM intake, because the intake of these nutritional fractions is related to their dietary concentrations and also to the DM intake. In this study, the concentrations of these fractions did not differ across the experimental diets (Table 2).

The peanut cake levels did not affect (P > 0.05) digestibility of DM, CP, OM, NDF, NFC, and TDN (Table 4); however, a positive linear effect (P = 0.035) on apparent total EE digestibility in the diets with peanut cake was observed. According to Palmquist (1991), increased EE intake promotes lower endogenous loss of lipid compounds, which increases the apparent digestibility. Silva et al. (2015) found that the substitution of soybean meal with peanut cake did not compromise nutrient digestibility in diets for goats.

View Full Table | Close Full ViewTable 4.

Nutrient digestibility coefficient (%) of diets with soybean meal substituted for peanut cake from biodiesel production

Rate of substitution of soybean meal for peanut cake, %
Item 0 33 66 100 SEM Lin1 Quad2
DM 57.15 59.57 57.36 59.09 0.937 0.647 0.897
OM 60.00 62.47 60.50 61.97 0.885 0.602 0.818
CP 67.32 70.63 69.23 67.25 1.040 0.878 0.224
EE3 54.00 66.83 63.34 67.12 1.868 0.035 0.259
NDF4 25.80 40.51 35.01 39.48 4.240 0.337 0.574
NFC5 89.57 81.43 80.20 83.28 3.587 0.526 0.442
TDN 60.42 63.55 61.91 63.78 0.897 0.285 0.764
Regression equation
EE Ŷ = 57.1728 + 0.109813X r = 0.60
1Linear effect.
2Quadratic effect.
3EE = ether extract.
4Value corrected for ash and protein.
5NFC = nonfiber carbohydrates.

Santos et al. (2012) analyzed protein byproducts and found that peanut cake had the most potential for replacing soybean meal because effective DM degradation was similar to that of soybean meal.

According to Nagaraja et al. (1997), unsaturated fatty acids are typically toxic to Gram-positive bacteria, perhaps by altering cell membrane permeability, thereby decreasing the cell’s ability to regulate intracellular pH and obtain nutrients. Doreau and Chilliard (1997) confirmed that the dietary addition of up to 5% EE may affect fiber carbohydrate digestion. However, in the current study, the replacement of soybean meal with peanut cakes increased the EE concentration but did not decrease NDF digestibility (the EE levels remained below 3.51%).

The substitution of soybean meal for peanut cake did not affect final BW, when Nellore bulls were weighed after 12 h of fasting before being slaughtered (P = 0.082), or feed efficiency (P = 0.277). Average daily weight gain had a negative linear effect (P = 0.015) due to the low DM intake ratio driven by the peanut cake levels. Although the diets contained similar protein and energy levels, the higher lipid content in the peanut cake affected intake and ADG. The higher lipid levels may be favorable because they increase the energy density; however, the increased intake of this fraction may reduce total DM intake, consequently reducing CP, vitamin, and mineral intake, explaining the change in ADG.

The substitution of soybean meal with peanut cake did not affect feed conversion (Table 5). The variables used to calculate feed conversion, DM intake, and ADG behaved in a similar, decreasing manner, resulting in similar G:F results.

View Full Table | Close Full ViewTable 5.

Productive performance in feedlot-finished young bulls fed diets containing soybean meal substituted for peanut cake

Rate of substitution of soybean meal for peanut cake, %
Item 0 33 66 100 SEM Lin1 Quad2
Final BW, kg 510.06 497.00 498.62 477.94 5.974 0.082 0.733
ADG, kg 1.41 1.31 1.28 1.04 0.050 0.015 0.524
Feed efficiency 0.134 0.129 0.133 0.125 0.003 0.277 0.703
Regression equation
ADG Ŷ = 1.43138 − 0.0034394X r = 0.89
1Linear effect.
2Quadratic effect.

Final BW and average daily weight gain were similar to those found reported by Mandarino et al. (2013), who evaluated the production and economic performance of zebu cattle in confinement.

Nitrogen intake (P = 0.002) and plasma urea N values (P = 0.002) was linearly decreased by the substitution of soybean meal for peanut cake (Table 6). However, fecal N levels, digested N (in g/d and in % ingested N), and urine urea N (in g/d and g/L) were not affected (P > 0.05) by increasing levels of peanut cake.

View Full Table | Close Full ViewTable 6.

Nitrogen balance in feedlot-finished young bulls fed diets containing soybean meal substituted for peanut cake

Rate of substitution of soybean meal for peanut cake, %
Item 0 33 66 100 SEM Lin1 Quad2
Ingested N, g/d 260.80 236.79 232.00 185.60 3.340 0.002 0.424
Feces N, g/d 74.64 76.75 74.62 65.93 3.110 0.484 0.533
Urine N, g/d 51.49 67.59 56.75 37.87 3.121 0.212 0.065
Retained N, g/d 134.67 92.45 100.63 81.80 2.115 0.062 0.073
Nitrogen balance, % 51.44 39.04 43.38 44.07 1.820 0.342 0.224
Urine urea, g/d 11.05 14.50 12.18 8.13 0.670 0.212 0.065
Urine urea N, g/L 4.83 6.81 5.84 3.52 0.365 0.314 0.054
Plasma urea N, g/L 0.22 0.18 0.19 0.15 0.007 0.005 0.903
Regression equation
Ingested N, g/d Ŷ = 263.2900 − 0.693400X r = 0.89
Plasma urea N Ŷ = 0.2167 − 0.0005921X r = 0.87
1Linear effect.
2Quadratic effect.

The decrease in N intake occurred due to a decrease in DMI, because the diets had similar levels of CP (Table 2). Pereira et al. (2007) analyzed dietary N levels for beef cattle and showed that increased N intake is an expected consequence of increased dietary CP levels. The direct relationship between intake of DM and of N was found in other studies with ruminants (Eiras et al., 2014; Nicory et al., 2015; Valero et al., 2015; Palmieri et al., 2016).

Nitrogen intake is linked to urea production in the liver and urea excretion via the urine. Low intake reduces urea excretion in the urine to maintain the plasma urea pool, which is under homeostatic control (Van Soest, 1994). In the current study, N intake was optimal (NRC, 2000), which is reflected by the observation that N excretion in the feces and urine were similar, as observed by da Silva et al. (2016).

The urea N concentrations in the blood plasma linearly decreased (P = 0.005) as soybean meal was increasingly replaced with peanut cake. This decrease may be attributable to the decrease in CP intake and improvement of CP utilization in ruminal metabolism, resulting in lower ruminal ammonia production by peanut cake protein. According to Harmeyer and Martens (1980), the amount of urea synthesized by the liver is proportional to the concentration of ammonia produced in the rumen. Consequently, its blood concentration is directly related to protein intake and the energy:protein ratio in the diet.

The N balance was positive for all of the diets, confirming protein was retained in the animal, leading to weight gain. However, as peanut cake replaced soybean meal, there was a decrease in the concentration of blood plasma urea, indicating that the protein from this byproduct is used more efficiently by ruminant metabolic systems.

The N synthesis and crude microbial protein were unaffected (P > 0.05) by the experimental diets (Table 7).

View Full Table | Close Full ViewTable 7.

Nitrogen microbial and microbial protein synthesis in feedlot-finished young bulls fed with diets containing soybean meal substituted for peanut cake

Rate of substitution of soybean meal for peanut cake, %
Item 0 33 66 100 SEM Lin1 Quad2
Microbial N, g/d 218.83 181.64 235.34 203.78 14.271 0.939 1.000
Uric acid, mmol/d 11.84 13.49 14.62 16.07 0.632 0.101 0.950
Allantoin, mmol/d 280.90 236.76 297.34 259.04 16.595 1.000 1.000
Purine derivatives, mol/d 292.74 250.26 311.96 275.11 16.575 0.945 0.975
Absorbed purines, mol/d 300.98 249.84 323.70 280.29 19.628 0.939 1.000
1Linear effect.
2Quadratic effect.

Microbial protein synthesis was not affected by the experimental diets because they contained similar nutritional fractions, such as NFC and CP. According to Dewhurst et al. (2000), microbial growth increases with the combined increase in fermentable energy and degradable N in the rumen. Microbial protein synthesis is dependent on carbohydrate and N availability in the rumen (NRC, 2000).

According to Firkins et al. (1998), microbial synthesis can be affected by the level of concentrate in the diet and by the percentage of fiber that influences the rumen pH and availability of degradable protein in rumen. In the present study, purine derivatives and microbial N production was not affected by the levels of peanut cake, showing the balance between diets without excess or limitation of N for rumen metabolism. Silva et al. (2016) tested another protein source (cottonseed cake) in a ruminant diet and also did not find alterations in microbial N production. This observation corroborates data from Van Soest (1994), who observed that increased intake leads to greater escape of microorganisms into the duodenum.

Peanut cake should not be used to replace soybean meal in the diets of young bulls being finished in a feedlot because the substitution reduces the intake of several nutritional fractions and decreases performance. The use of peanut cake does not alter microbial protein synthesis and positively affects N balance, but these factors do not justify its use.




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