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Desempenho de novilhos Nelore em pastagem de Panicum maximum Jacq. cv. Mombaca recebendo cana-de-acucar picada e suplementacao proteica.

Performance of Nellore steers grazing on Panicum maximum Jacq cv. Mombaca receiving chopped sugar cane tops and protein supplementation.

Introduction

Animal nutrition has generally been recognized as being basically dependent on four factors: animal requirements, feedstuff nutrient content and digestibility, and finally, animal feed intake. In this consideration, to optimize ruminant production from pasture it is necessary to adjust the seasonal deficit of nutrients required by the animals, and improve forage digestibility and intake, mainly through supplementation.

Tropical forages usually show nutritional deficiencies that depreciate while the plant matures and the effect is pronounced during the dry season. Forage growth is mainly dependent on temperature, light and precipitation. In tropical regions, during the dry season animal production is limited by quality and forage availability. Brazilian beef production systems are supported mainly by pasture, which increases the importance of a correct grazing management that allows animals to obtain essential nutrients for good performance.

Beef farms in Brazil have mainly cultivated pastures represented by Brachiaria and Panicum species, and nutritional deficiency during the dry season is commonly observed. Intake by range ruminants has a positive correlation with forage availability, implying that a reduction of forage availability can reduce feed intake. A curvilinear relationship between daily forage allowance and daily forage intake has been demonstrated in many experiments, as revised by Gibb (2006). From such relationships, it is evident that to achieve unrestricted daily intakes, daily allowances equivalent to between 3 and 4 times maximum daily intake must be provided. Low forage mass allowance can be partially compensated by longer grazing time; however, total forage intake by animals may remain negatively affected (DIAS et al., 2008).

Protein supplementation allows an increase in forage digestibility and intake (MOORE et al., 1999) in grazing systems. In cattle consuming low-quality forage, protein supplementation has consistently increased N retention (FARMER et al., 2004). In diets based on poor quality forages, protein supplementation can increase beef steers production (KIM et al., 2007), making it possible for animals to obtain higher gains on pasture.

This research was conducted to evaluate protein supplementation on the performance of Nellore steers grazing on Mombaca grass (Panicum maximum Jacq cv. Mombaca) and receiving chopped sugar cane tops during the dry season.

Material and methods

Thirty-two Nellore steers with average initial live weight of 300 kg ([+ or -] 25.80) were used in a grazing experiment in which they received protein supplementation. The experiment was conducted in the Northwest of Parana State, Brazil, from May to September, 2003. The region's climate is classified as Cfa (PEEL et al., 2007).

Steers were randomly distributed into four treatments and grazed on Mombaca grass (Panicum maximum Jacq cv. Mombaca) using continuous grazing. All steers, regardless of treatment, were supplemented with chopped sugar cane at the rate of 0.80% of live weight (LW) on DM basis, and protein supplement at the rate of 0.40% of LW. Sugar cane composition (dry matter basis) was: 28.30% dry matter (DM), 4.52% crude protein (CP), 6.20% mineral matter (MM), 1.55% ether extract (EE), 34.10% acid detergent fiber (ADF), 7.60% lignin (L), 80.13% total carbohydrates (TC), and 43.88% neutral detergent fiber (NDF). IVDMD of chopped sugar cane was 50.37%. Treatments were four supplements with different concentrations of CP, as follows: 12.5, 25.0, 32.5 and 50.0% CP. In relation to LW, supplements supplied 0.05, 0.10, 0.15 and 0.20% of CP. Mineral salt was supplemented along with protein supplements. Chemical composition of feeds is shown in Table 1, and percent and chemical composition of supplements are shown in Table 2.

There was an adaptation phase of 15 days, following which steers were randomly separated into four groups. Steers were weighted at the beginning of the experiment and then every 28 days after 14h of complete fasting. Considering chopped sugar cane and protein supplement, steers were fed at the rate 1.20% of LW. The amount of sugar cane and protein supplement fed was adjusted every 28 days considering the weight of steers. These data were then used to calculate the dry matter intake (DMI) and feed efficiency (FE) based on both supplements (chopped sugar cane and protein supplements).

The experimental area, 4.50 hectares, consisted of four paddocks measuring 1.125 ha each. The area was divided by electric fences and had a permanent supply of water and feeding troughs strategically placed. The paddocks were not grazed for 50 days before the start of the experiment to guarantee a high availability of initial forage mass. The estimation of forage mass (FM) availability was done every 28 days after the start of grazing using the double sampling method (WILM et al., 1944). This involved randomly cutting four 1-[m.sup.2] samples per paddock at 20 cm above ground. Herbage samples were divided in two sub-samples, one to determine dry matter and another to evaluate plant components which were separated for green leaf blade (GLB), stem + green sheath (SGS) and dead material (DMT). Samples were then dried at 55[degrees]C for 72h and ground in a Willey mill ([R] Tecnal) using a 1-mm screen. Steers were switched between paddocks every week to reduce possible effects of forage availability. The orts in feeders were collected and weighted daily, and sampled twice a week to determine DM and CP. These data were used to determine DM and CP daily intake.

Samples were analyzed for dry matter (DM), crude protein (CP) and organic matter (OM) according to AOAC (1994), and for neutral detergent fiber (NDF) (VAN SOEST et al., 1991). In vitro dry matter digestibility (IVDMD) was conducted using Tilley and Terry (1963). The procedure was run in a batch fermentation vessel [DAYSI.sup.II]/ANKON [R] (ANKON Technology Corp., Fairport, NY, USA). The IVDMD values were used to calculate the digestible organic matter (DOM) and the total digestible nutrients (TDN) using the equations of Kunkle and Bates (1998):

DOM = - 0.664 + (1.032 (IVDMD))

where:

DOM = digestible organic matter (%); IVDMD = in vitro dry matter digestibility (%).

TDN = (OM (26.8 + 0.595 DOM)) / 100

where:

OM = organic matter (%); DOM = digestible organic matter (%).

Data were analyzed using the GLM procedure of SAS (2000), Release 8.1. Data on forage availability and forage characteristics (FM, GLB, SGS, DMT and GLB/SGS) were analyzed considering time of year (1, 2 and 3) as the independent variable using the model:

[Y.sub.ij] = [mu] + [T.sub.i] + [.sub.ei]j

where:

[Y.sub.ij] = dependent variable; [mu] = overall mean; [T.sub.i] = effect of period of the year and [e.sub.ij] = error effect.

Animal performance data were analyzed for the effect of treatments (protein supplements) using the model:

[Y.sub.ijk] = [mu] + [T.sub.i] + [e.sub.ijk]

where:

[Y.sub.ijk] = dependent variable; [mu] = overall mean; [T.sub.i] = treatment effect and [e.sub.ijk] = error effect.

Averages were compared using Tukey test at 5% significance. P values between 0.05 and 0.10 were considered as showing a tendency.

Results and discussion

There was no influence of periods (p > 0.05) on forage mass (FM), stem + green sheath (SGS) and dead material (DMT) (Table 3). There was a tendency (p = 0.087) of decrease in green leaf blade (GLB), but GLB/SGS ratio remained similar across the periods.

During the dry season in Brazil, tropical pastures show a slow growth rate (CANTO et al., 2002) and consequently a decrease in FM is normal as a result of continuous or rotational grazing. In this experiment, the pasture was deferred and FM accumulated before experimental period. Pasture management should observe more than a minimum of FM availability to allow unconstrained DMI. The FM observed in this research was 10,069 kg [ha.sup.-1] and provided more than 3 to 4 times intake (GIBB, 2006).

Under grazing, there is a close relationship between leaf proportion (O'DONOVAN; DELABY, 2005), green leaf mass (SMIT et al., 2005) and dry matter intake. Considering the FM and GLB observed in the present experiment, it can be assumed that steers were exposed to abundant forage and therefore had the opportunity to graze selectively. Regardless of period, GLB represented a substantial proportion of forage mass, which was higher than 19.5% (Table 3), and had high availability (> 1900 kg [ha.sup.-1]) (Table 3).

Forage mass decreased by 952 kg from the first to the last evaluated period, especially as a result of a decrease in GLB that reduced to 707 kg [ha.sup.-1]. Decrease in GLB was the result of animal preference, as also observed by Brancio et al. (2003) with steers grazing three different Panicum cultivars, where animals showed high selectivity for green leaves (92.4%) and low selectivity for stems (6.7%).

The GLB/SGS ratio indicates forage quality and as it is higher the pasture offers the animals forage with better nutritive value. The mean GLB/SGS ratio (0.34) shown in Table 3 was lower for Mombaca grass than normally occurs in this period in Brazil (CANDIDO et al., 2005), and probably as a consequence of the high production of reproductive tillers and pasture height (96 cm). Candido et al. (2005), evaluating Mombaca grass pasture and using 44 to 63 days of grazing interval, found a GLB/SGS ratio of 0.43 for a pasture height of 68.6 cm after grazing. Euclides et al. (2008) evaluated Mombaca grass under grazing, for four years and also verified a higher GLB/SGS ratio, which ranged from 0.39 to 0.43. The lower GLB/SGS ratio seen in our experiment probably did not limit intake because the pasture showed a high GLB (2,195 kg [ha.sup.-1]) that could be give to the animals possibility of high selection.

Data for qualitative characteristics of Mombaca grass during different periods are shown in Table 4.

Crude protein in FM was highest in period 1 and lowest in period 3 (p = 0.053). Also, there was a tendency (p = 0.06) of CP in GLB to differ in the different periods. The IVDMD showed a tendency (p = 0.059) to increase from period 1 to period 3 in GLB, while NDF showed a tendency to decrease (p = 0.078). The NDF in GLB and IVDMD in DMT were both affected (p < 0.05) by period whereby the NDF in GLB showed the highest value (56.8%) in period 1 and the lowest (54.5%) in period 3.

Regardless of forage component and significance, Table 4 shows for all forage components, lower value of NDF in period 3 which is associated with the start of re-growth.

The results for IVDMD (49.8%) are lower than observed by Canto et al. (2002), who reported IVDMD of 53%, but this author managed pasture to maintain a lower height. Euclides et al. (2008) evaluated Mombaca grass under grazing for four years and verified a higher organic matter in vitro digestibility which ranged from 58.10% before grazing to 50.30 after grazing. Protein supplements had an associative effect in relation to the use of available forage in the pasture, causing changes in the digestibility and forage intake (MOORE et al., 1999).

Considering initial and final weight, the average live weight was 325.75 kg (Table 5), and supplement fed (0.4% LW), the intake of protein supplement was on average 1.30 kg [day.sup.-1], and crude protein intake ranged from 0.163 kg [day.sup.-1] for 12.5% CP supplement to 0.650 kg [day.sup.-1] for 50% CP supplement. In relation to LW protein intake ranged from 0.05 to 0.20%.

Moore et al. (1999) reviewed the effects of supplementation on cattle performance and reported that in terms of protein supplementation the best results can be obtained if protein is supplied over 0.05% of LW. This level was attained using supplement with 12.5% CP, and higher supplementation did not influence (p > 0.05) ADG (Table 5) which averaged 0.61 kg [day.sup.-1].

Using an average LW (average of initial and final weight) of 325.75 kg and based on NRC (2000), dietary CP should be near 8.5% for 0.6 kg of ADG. Daily gain obtained in this study was very close to 0.6 kg day-1, showing that in this situation, intake of NE limited the ADG such that a 12.5% CP supplement was enough. At least 7% crude protein is necessary in the diet to sustain microbial growth and support efficient fibrous carbohydrate digestion of low-quality forages (LAZZARINI et al., 2009). Supplementation with nitrogen compounds in quantities that raise the crude protein content in the diet to levels close to 9% optimizes the use of low-quality forage by cattle under grazing (FIGUEIRAS et al., 2010).

The average daily gain observed in this experiment was higher than the gain reported by Zanetti et al. (2000) that also supplemented steers (207 kg LW) grazing Brachiaria decumbens with chopped sugar cane and protein supplement. These authors supplemented 10.5 kg [day.sup.-1] of chopped sugar cane, and 0.65 kg of a supplement with 52.5% CP, and reported gain of 0.36 kg LW [day.sup.-1]. Zanetti et al. (2000) supplied a total of 0.34 kg [day.sup.-1] of crude protein, which should be enough for higher gains, but the low forage availability (< 3,000 kg [ha.sup.-1]) may have compromised performance.

Using a protein supplement with 18% CP for steers grazing on Brachiaria brizantha cv. Marandu, fed at level of 1% LW, Canesin et al. (2007) verified a daily average gain of 0.51 to 0.57 kg [day.sup.-1]. Goncalves et al. (2007) supplemented steers grazing on native pasture with full fat rice bran at level of 0.5% LW and verified average daily gain of 0.55 kg [day.sup.-1]. Both results are inferior to our supplementation, but these authors used more supplement in relation to LW.

Canto et al. (2002) working with Tanzania grass without grazing for 70 days, in the same region and in the same season of the year, supplemented steers only with salt plus urea as nitrogen source and obtained lower gains, between 135 and 195 kg [ha.sup.-1], as result of lower stocking rate (1.8 to 3.2 AU [ha.sup.-1]). In our experiment, stocking rate ranged from 4.75 AU [ha.sup.-1] (start) to 5.55 AU ha-1 (end) much higher than Canto et al. (2002), which give a gain of 364 kg [ha.sup.-1].

Conclusion

The use of protein supplement (with 12.5% CP, DM basis) at the rate of 0.4% of LW mixed with chopped sugar cane tops fed at the rate of 0.8% of LW for beef production in Mombaca pasture with high forage mass availability can produce steer gains of 0.6 kg of LW [day.sup.-1] and 350 kg of LW [ha.sup.-1] during the dry season (May to September).

DOI: 10.4025/actascianimsci.v32i4.8142

Received on September 11, 2009.

Accepted on August 27, 2010.

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Antonio Ferriani Branco (1) *, Geraldo Moreli (2), Cloves Cabreira Jobim (1), Ulysses Cecato (1), Katia Cylene Guimaraes (3) and Silvana Teixeira (1)

(1) Departamento de Zootecnia, Centro de Ciencias Agrarias, Universidade Estadual de Maringa, Av. Colombo, 5790, 87020-900, Maringa, Parana, Brazil. (2) Instituto Paranaense de Assistencia Tecnica e Extensao Rural, Apucarana, Parana, Brazil. (3) Instituto Federal de Educacao, Ciencia e Tecnologia Goiano, Rio Verde, Goias, Brazil. *Author for correspondence. E-mail: afbranco@uem.br
Table 1. Chemical composition of feeds (% DM).

                                    Nutrients

                                 % of dry matter

Ingredients      DM     CP    MM    EE    NDF    ADF      TDN

Soybean meal    88.4   48.5   6.0   1.6   12.0    9.0   84.0 (1)
Soybean hulls   90.7   11.0   4.5   2.7   55.7   42.6   80.0 (1)

(1) Estimated using NRC (2000).

Table 2. Ingredient and chemical composition of supplements
(DM basis, %).

                                   Protein content (%)

Ingredients               12.5       25.0       37.5       50.0

Soybean hulls (%)         95.32      87.40      70.18      47.81
Soybean meal (%)           --         3.36      17.76      37.67
Urea (%)                   0.78       4.62       7.08       9.18
Ammonium sulfate (%)       0.06       0.78       1.14       1.50
Mineral salt (%) (1)       3.84       3.84       3.84       3.84
Total (%)                100.00     100.00     100.00     100.00

                          Chemical composition of supplements
                                       (DM basis)

MS (%)                   91.10      91.50      91.40      91.20
CP (%)                   12.80      25.60      37.90      50.70
EE (%)                    2.60       2.40       2.20       1.90
MM (%)                    4.30       4.10       4.20       4.40
NDF (%)                  52.20      50.00      39.20      32.50
ADF (%)                  40.60      37.50      31.50      23.80
TDN (%) (2)              76.10      72.50      70.80      69.80

(1) Mineral salt composition [kg.sup.-1]: Ca 130 g; P 65 g; S 12 g;
Mg 12 g; Na 135 g; Cu 155 mg; Zn 3080 mg; Mn 1050 mg; Co 63 mg;
I 63 mg; Se 18.2 mg and Fe 2680 mg. 2NRC (2000).

Table 3. Forage mass (FM), green leaf blade (GLB), stem +
green sheath (SGS), dead material (DMT) and GLB/SGS ratio of
Mombaca grass pasture.

                                   Period (1)

Variables                   1           2           3

FM (kg [ha.sup.-1])       10679       9801        9727
GLB (kg [ha.sup.-1])      2610        2073        1903
SGS (kg [ha.sup.-1])      6559        6336        6225
DMT (kg [ha.sup.-1])      1510        1392        1599
GLB/SGS                   0.40        0.33        0.31

Variables                Average     SEM (2)     P value

FM (kg [ha.sup.-1])       10069      190.640      0.467
GLB (kg [ha.sup.-1])      2195       80.000       0.087
SGS (kg [ha.sup.-1])      6373       153.908      0.894
DMT (kg [ha.sup.-1])      1500       50.200       0.664
GLB/SGS                   0.34        0.013       0.175

(1) Periods corresponded to 1= 7/25; 2 = 8/22; and 3 = 9/19;
2SEM = Standard Error of Mean.

Table 4. Average contents of crude protein (CP) and neutral
detergent fiber  (NDF)  and in vitro dry matter digestibility
(DMIVD) of Mombaca grass.

                                        Period (1)

Variables                    1              2              3

Forage mass (FM)

CP (%)                    7.24           6.80           6.58
NDF (%)                  63.54          62.41          61.94
IVDMD (%)                49.76          48.99          50.65

Green leaf blade (GLB)

CP (%)                   14.41          12.31          12.59
NDF (%)                  56.77 (a)      55.97 (ab)     54.49 (b)
IVDMD (%)                58.19          56.78          59.88

Stem + green sheath (SGS)

CP (%)                    5.44           5.44           5.24
NDF (%)                  64.72          63.40          63.08
IVDMD (%)                50.45          49.94          51.58

Dead material (DIMT)

CP (%)                    4.52           4.50           4.52
NDF (%)                  68.97          67.14          66.36
IVDMD (%)                32.67 (b)      33.51 (b)      36.21 (a)

Variables                 Average        SEM (2)        P value

Forage mass (FM)

CP (%)                      6.87          0.069          0.053
NDF (%)                    62.63          0.222          0.238
IVDMD (%)                  49.80          0.260          0.358

Green leaf blade (GLB)

CP (%)                     12.77          0.119          0.060
NDF (%)                    55.74          0.227          0.035
IVDMD (%)                  58.28          0.322          0.059

Stem + green sheath (SGS)

CP (%)                      5.38          0.032          0.244
NDF (%)                    63.73          0.222          0.193
IVDMD (%)                  50.66          0.311          0.490

Dead material (DIMT)

CP (%)                      4.51          0.024          0.984
NDF (%)                    67.49          0.290          0.078
IVDMD (%)                  34.13          0.323          0.008

(ab) Values in the row with different superscripts means
significant difference (p < 0.05) by Tukey test. (1) Periods
corresponded to 1 = 7/25, 2= 8/22 and 3 = 9/19; (2) SEM =
Standard Error of Mean.

Table 5. Initial and final live weight and average daily gain
(ADG) of steers.

                                  Treatments
                                                                   SEM
Variables               12.5%   25.0%   37.5%   50.0%   Average    (1)

Initial LW (kg)          303     301     297     300    300.25    4.565
Final LW (kg)            354     354     349     348    351.25    5.340
ADG (kg [day.sup.-1])   0.610   0.634   0.616   0.568    0.607    0.028

(1) SEM = Standard Error of Mean.
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Title Annotation:texto en ingles
Author:Ferriani Branco, Antonio; Moreli, Geraldo; Cabreira Jobim, Cloves; Cecato, Ulysses; Cylene Guimaraes
Publication:Acta Scientiarum Animal Sciences (UEM)
Date:Oct 1, 2010
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