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Ruminal digestion and chemical composition of new genotypes of buffelgrass (Cenchrus ciliaris L.).

SUMMARY

This study evaluates and compares the dry matter production (TDM), chemical composition and effective degradability of dry matter (EDDM), crude protein (EDCP) and neutral detergent fiber (EDNDF) of the Nueces hybrid and five new genotypes of buffelgrass growing in Northeastern Mexico. Potential intake of minerals by cattle consuming the new genotypes was also estimated. All grasses were established in a completely randomized design with three replicates in a rain fed experiment. Plants were hand harvested on Nov. 14, 2000 at Nuevo Leon, Mexico. TDM was not significantly different among genotypes. Crude protein content and cell wall and its components (cellulose, hemicellulose, and lignin) were significantly different among grasses. Also, EDDM, EDCP, and EDNDF were significantly different among the buffelgrass genotypes. The Nueces hybrid had the highest degradability values; in contrast, PI 2 had the lowest values. It seems that high lignin content in new genotypes may negatively influence nutrient digestion in the rumen of sheep. Only the K, Fe and Co contained in all grasses would be sufficient to meet the requirements of grazing cattle. Data of dry matter production and nutritional dynamics, suggest that the new genotypes PI 1 and PI 4 could be considered as good substitutes of the Nueces hybrid for grazing ruminants in northeastern Mexico.

KEYWORDS / Buffelgrass / Grass Genotypes / Nutrient Digestibility / Northeastern Mexico / Ruminants /

Received: 10/29/2002. Modified: 03/20/2003. Accepted: 03/25/2003

Introduction

Common buffelgrass (T-4464) was introduced into Texas in the late 1940s and it is currently grown on 8 to 10 million acres in Southern Texas, USA, and the North of Mexico. Since introduction, buffelgrass has had a marked impact on the livestock industry of these regions since, as a range grass, it is highly productive and has allowed an increase in cattle stocking rates from one animal unit (AU) for every 12ha to 1 AU for 4ha (Hanselka, 1985). Buffelgrass reproduces by obligated apomixis, in which seeds are formed without sexual fertilization. Consequently, the progeny are genetically identical to the maternal parent. The monoculture of this grass with its unique type of reproduction encompasses millions of ha with genetically identical plants, and represents a high risk due to the susceptibility to diseases or pests. Recently, a blight of epidemic proportions on common buffelgrass has been reported in Mexico and South Texas. The causal agent has been identified as Pyricularia grisea (Cook) Sacc. (Rodriguez et al., 1999). Because of this and other potential problems, new strains, cultivars, and hybrids of buffelgrass have been tested in order to increase the genetic pool of this grass in the region.

Because of its wide adaptation to semiarid regions and relatively good nutritional quality, buffelgrass is considered as a South Texas and Northeastern Mexico wonder grass (Hanselka, 1988). However, seasonality of rainfall and temperature are major influences on nutritional quality of buffelgrass (White and Wolfe, 1984). Silva and de Faria (1995) reported significant differences in the nutritional value among new cultivars and hybrids of buffelgrass; moreover, the rate and extent of ruminal digestion of the nutrients contained in forage of new genotypes has not been reported in the scientific literature. Thus, effective degradability and the rate of digestion are important characteristics of forage that may be used to predict the nutritive value more accurately and compare the utility of this kind of forages in the diets for ruminants (Orskov, 1991). Grasses are important sources of organic and inorganic nutrients for ruminants; however, in some circumstances, they are deficient in one or more of these nutrients. Minerals are required to meet the animal needs for optimum development and health (Spears, 1994), as they are essential nutrients and influence animal performance (McDowell, 1997). The object of this study was to evaluate and compare the nutrient content and ruminal fermentation of forage of five strains and one hybrid of buffelgrass under rain feed conditions in Northeastern Mexico

Materials and Methods

Research was carried out at the Experimental Station "General Teran", Instituto Nacional de Investigaciones Forestales, Agricolas y Pecuarias (INIFAP) and at the Universidad Autonoma de Nuevo Leon (UANL). General Teran, N.L., Mexico, is located at 25[degrees]18'N and 99[degrees]35'W, with an altitude of 332masl. The climate is typically semitropical and semiarid with warm summers. The predominant type of vegetation is known as the Tamaulipan Thorn scrub or subtropical Thorn scrub woodlands. The dominant soils are deep, dark-gray, lime-clay Vertisoles resulting from alluvial processes. These soils are characterized by high Ca carbonate (pH 7.5-8.5) and relatively low organic matter content. Annual mean temperature is 22.4[degrees]C, average yearly rainfall 784 mm and evaporation 1622mm.

Under rain fed conditions, five strains of buffelgrass (Cenchrus ciliaris L.) identified as PI-307622 (PI 1), PI-409252 (PI 2), PI-409375 (PI 3), PI-409443 (PI 4), PI-409460 (PI 5), and the hybrid Nueces were established in experimental plots, using a completely randomized design with three replicates. The plots consisted of 5m long rows, with 0.8m between rows. With the purpose to achieve a uniform grass growth, all grasses were cut prior to the experiment, in March 2000. The first significant rainfall of that year occurred on Sept. 14 (66mm) and provided the conditions to sustain grass growth. In Sept. and Oct., 452mm of rainfall were recorded, which allowed the grasses to reach full blossom by Nov. 14, when all grasses were hand harvested to a height of 0.15m above ground. Partial dry matter was determined after drying in an oven at 55[degrees]C for 72h. Blades and stems were split and weighed individually, and the proportion of blades (H%) for each sample was obtained. Then, samples were ground in a Wiley mill (1mm screen) and stored in plastic containers.

Samples were analyzed for dry matter (DM), organic matter (OM), crude protein (CP; AOAC, 1990), neutral detergent fiber (NDF), acid detergent fiber (ADF; Goering and Van Soest, 1970) and acid detergent lignin (ADL; AOAC, 1990). Hemicellulose (NDF-ADF) and cellulose (ADF-ADL) were estimated by difference. Estimation of insoluble [N.sub.2] in NDF (INNDF) and insoluble [N.sub.2] in acid detergent fiber (INADF), which corresponds to the non-degraded [N.sub.2], was performed according to Van Soest et al. (1991), and the slowly degraded [N.sub.2] associated to the cell wall components was calculated as INNDF minus INADF (Goering and Van Soest 1970; Krishnamoorthy et al., 1982).

Mineral content was estimated by incinerating the samples in a muffle oven at 550[degrees]C, during 4h. Ashes were digested in a solution containing HCI and HN[O.sub.3], using the wet digestion technique (Diaz-Romeau and Hunter, 1978). Concentrations of Ca, Na, K, Mg, Cu, Fe, Zn, Mn, Co, and Mo were obtained using an atomic absorption spectrophotometer, and the P content was determined in a colorimeter (AOAC, 1990).

The rate and extent of DM, CP and NDF digestibility in gasses were measured using the nylon bag technique. Four rumen fistulated Pelibuey x Rambouillet sheep (weighing 45.2 [+ or -] 2.3kg, BW) were used to incubate bags (5 x 10cm, 53 1/4[mu] pore size) containing ground samples (4g) of each grass replication and suspended in the ventral part of the rumen of each sheep. Throughout the experiment, sheep were fed alfalfa hay ad libitum. For each grass replication six bags were incubated for 4, 8, 12, 24, 36, and 48h. Upon removal from the rumen, bags were washed in cold running water. Zero time disappearance was obtained by washing non-incubated bags (Oh bag). All bags were dried at 60[degrees]C in an oven during 48h. Weight loss of DM, CP and NDF was recorded. Disappearance of DM, CP, or NDF for each incubation time was calculated as

Disappearance (%) = ([Initial weight - Final Weight]/Initial Weight) x 100

The disappearance of DM, CP, or NDF for each incubation time was used to estimate the digestion characteristics of DM, CP and NDF, using the equation of Orskov and McDonald (1979)

p = a+b (l-[e.sup.-ct]),

where p: disappearance rate at time t; a: an intercept representing the soluble portion of DM, CP or NDF at the beginning of incubation (time 0); b: portion that is slowly degraded in the rumen; c: rate constant of disappearance of fraction b; and t: time of incubation.

The nonlinear parameters a, b, and c and effective degradability of DM (EDDM), CP (EDCP) or NDF (EDNDF) = (a+b)c/(c+k)([e.sup.(ct)LT]), were calculated using the Neway computer program (McDonald, 1981); k is the estimated rate of outflow from the rumen and LT is the lag time. The EDDM, EDCP and EDNDF values were estimated assuming a rumen outflow rate of 2.0%/h. Total digestible DM/ ha (DDM) was calculated as TDM x EDDM and total digestible CP/ha (DCP) as TDM x EDCP.

Data of chemical composition, a, b, c, EDDM, EDCP, EDNDF, DDM and DCP were statistically analyzed using a one-way analysis of variance. Means were separated using the Least Significant Difference technique. Simple linear correlation analyses were performed between %H, chemical composition and EDDM, EDCP and EDNDF (Snedecor and Cochran, 1980).

Results and Discussion

The total dry matter (TDM) production was not significantly different among the evaluated genotypes (Table I). However, PI 4 and PI 2 yielded more dry matter than other grasses including the Nueces buffelgrass, which is recognized as highly productive and with good nutritional quality. The %H was significantly different among grasses, being Nueces and PI 4 the leafier grasses.

The CP content was significantly different among genotypes. PI 5 had the highest value and PI 3 the lowest. The mean value of CP in all genotypes was 8.3% (Table I). This value is about one percent above the minimal (7%) required to sustain rumen functionality (NRC, 1996). It appears that low N content in the forage is related with the available [N.sub.2] in the soil (Ramos and McDowell, 1994). The soil where this experiment was located has been characterized for its low [N.sub.2] availability (INIFAP, 1991). However, higher CP values were reported, only at the end of summer and the beginning of autumn, for the total plant in common buffelgrass (Ramirez et al., 2001a) and the hybrids Nueces (Ramirez et al., 2001b) and Llano (Foroughbackhch et al., 2001) growing in the same region but in different soil types.

The cell wall (NDF) content and its components (ADF, ADL, cellulose, and hemicellulose) were significantly different among grasses (Table I). Nueces resulted with the highest cell wall contents and PI 5 with the lowest. Moreover, PI 5 had the largest fully digestible portion of the DM (100NDF= 34.1%), and Nueces the lowest (28.2%). Also, Nueces contained less lignin (Table I). Lignification of the cell wall has been related to low degradability of nutrients contained in plants (Van Soest, 1994). The INNDF was not significantly different among grasses. Conversely, INADF and INNDF-INADF were significantly different. The [N.sub.2] non-available for ruminants, estimated by the faction INADF, was high (29.8%; mean value of all grasses) as compared with previous reports (3 to 15%; Van Soest, 1994).

Fraction a (lost during washing of bags) of DM, CP, and NDF was significantly different among the grasses. Conversely, fraction b (slowly degraded in the rumen of sheep) was not different (P<.05). The degradation rate (c, %/h) in DM and PC was different (P<0.05), but was not different (P>0.05) in NDF. The EDDM, EDNDF, and EDCP were significantly different among grasses (Table II). The hybrid Nueces had the highest value of EDDM, EDNDF, and EDCP while the strain PI 2 had the lowest values. Higher lignin content in the new genotypes might have decreased rumen fermentation of nutrients in the rumen of sheep. The EDCP overall mean was estimated to be 64.2% and the potential available CP (100-INADF) was 70.2%. The difference of 6% between these two values might be the amount of INNDF-INADF which is slowly available in the rumen of the animal, but could be fully digested in the abomasum (Van Soest, 1994; Van Soest, et al., 1991). Moreover, it seems that INADF negatively affected EDCP (r = -0.47, P<0.05).

The degradability values found in Nueces were higher than those reported by Ramirez et al. (2001b), who evaluated Nueces growing in these regions but harvested in different dates. High degradability values reported in the present study may be associated to the positive effects of high precipitation (Foroughbackhch et al., 2001; Ramirez et al., 2001a). In this experiment, more than 400mm fell during the growing season. The %H also influenced the effective degradability of nutrients in the grasses, since it correlated with EDDM (r= 0.63, P<0.05), and EDCP (r= 0.53, P<0.05). The EDCP was also positively correlated to CP content (r= 0.50, P<0.05), and negatively to INADF. This means that when CP increased, EDCP did as well.

There were no differences (P>0.05) in DDM among the grasses tested (Table II). The differences found in EDDM were overriden by the non-significant differences in forage production (TDM) among the genotypes. In contrast, there were significant (P>0.05) differences in DCP among the genotypes evaluated. The strain PI 4 had the highest value and PI 2 the lowest (Table II).

With exception of Ca, Fe, Mn, and Co, all minerals evaluated were significantly (P<0.05) different among genotypes (Table III). In general, most minerals had concentrations that are low for the needs of adult grazing cattle. It appears that soil characteristics did influence forage concentration of specific minerals. Forages growing in soils with high values of Ca carbonates and pH, and low organic matter content, such as the ones used in this experiment, tend to have lower content of most essential minerals (INIFAP 1991). White and Wolfe (1985) also reported low values for P (0.23%), Ca (0.30%), K (1.6%) and Mg (0.18%) in common buffelgrass harvested during the autumn season in Cotula, Texas, USA.

Table IV shows the potential mineral intake, calculated for each mineral appearing in Table III, by a cow of 400kgBW, with a daily intake of 10.2kgDM of the evaluated grasses. The potential intake of K, Fe, Co, Mn (only in PI 4), and Mo (only in Nueces), would be sufficient to meet the requirements of these minerals for a growing cow of 400kg grazing any of the genotypes tested in these soils. However, Ca, P, Na, Mg, Cu, and Zn, were lower than required. Deficiencies of P and Na have been reported and they occur in many grass species that grow in warm climates (McDowell, 1997). Thus, to obtain an optimal productivity of cattle grazing these grasses growing in this type of soil, the animals have to be supplemented with Ca, P, Na, Mg, Cu, Zn, Mn (except for PI 4), and Mo (except for Nueces).

Conclusions

Forage dry matter production and total digestible dry matter were not significantly different among evaluated grasses. However, there were significant differences for most of the chemical components and digestion parameters. The hybrid Nueces had higher values of EDDM, EDNDF, and EDCP than the other grasses. High lignin content in the forage of new genotypes may decrease the amount of nutrients degraded in the rumen of sheep. In general, the mineral content in all grasses was low for the needs of grazing ruminants, an effect probably caused by the low mineral content in the soil. Only K, Fe, and Co would be sufficient to fulfill the requirements of a mature cow grazing the evaluated grasses, while other minerals have to be supplemented for an optimal cattle growth. As new genotypes had very similar dry matter production and nutritional dynamics, it is suggested that they could be used as forage substitutes of Nueces buffelgrass growing in the region.
TABLE I
DRY MATTER PRODUCTION (ton/ha), CRUDE PROTEIN, CELL
WALL COMPONENTS AND NITROGEN ASSOCIATED TO CELL WALL
(%) IN THE FORAGE OF THE HYBRID NUECES AND FIVE NEW
GENOTYPES OF BUFFELGRASS

Concept                           Genotype

                  Nueces       PI 1         PI 2        PI 3

TDM               4.8 (a)     5.2 (a)      3.8 (a)     3.5 (a)
%H                0.71 (a)    0.66 (ab)    0.49 (c)    0.63 (b)
Organic matter   88.5 (a)    85.9 (c)     87.7 (b)    87.0 (b)
Crude Protein     8.4 (c)     7.8 (de)     8.1 (cd)    7.5 (e)
NDF              71.8 (a)    69.7 (b)     70.4 (b)    69.7 (b)
ADF              47.9 (c)    51.6 (a)     49.8 (b)    50.8 (ab)
Hemicellulose    23.9 (a)    18.1 (c)     20.6 (b)    18.9 (c)
Cellulose        38.3 (b)    33.2 (d)     40.2 (a)    37.7 (bc)
ADL               5.3 (d)     8.5 (a)      6.9 (c)     7.5 (b)
INNDF            48.7 (a)    46.6 (a)     48.5 (a)    45.9 (a)
INADF            27.3 (b)    32.8 (a)     30.7 (ab)   35.0 (a)
INNDF-INADF      21.5 (a)    13.8 (bc)    17.7 (ab)   10.9 (c)

Concept                   Genotype

                   PI 4        PI 5       Mean [+ or -] SE

TDM               5.6 (a)     4.1 (a)     4.5  [+ or -] 0.4
%H                0.71 (a)    0.66 (a)    0.65 [+ or -] 0.02
Organic matter   86.4 (c)    86.6 (c)    87.0  [+ or -] 0.2
Crude Protein     8.8 (b)     9.2 (a)     8.3  [+ or -] 0.1
NDF              70.4 (b)    65.9 (c)    69.6  [+ or -] 0.5
ADF              48.8 (bc)   50.6 (ab)   49.9  [+ or -] 0.3
Hemicellulose    21.6 (b)    15.2 (d)    19.7  [+ or -] 0.7
Cellulose        36.3 (c)    40.3 (a)    37.6  [+ or -] 0.6
ADL               8.1 (a)     6.6 (c)     6.7  [+ or -] 0.7
INNDF            36.0 (a)    45.8 (a)    45.2  [+ or -] 1.2
INADF            21.7 (c)    31.2 (ab)   29.8  [+ or -] 1.2
INNDF-INADF      14.3 (bc)   14.6 (bc)   15.5  [+ or -] 1.1

(abcd) Indicate difference (P<.05) among values in a row.

TDM: total dry matter production; %H: ratio between leaf
blades and plant total weight; NDF: neutral detergent fiber;
ADF: acid detergent fiber; ADL: acid detergent lignin; INNDF:
insoluble [N.sub.2] in NDF as % of the total crude protein;
INADF: insoluble [N.sub.2] in ADF as % of the total crude
protein; INNDF-INADF: slowly degraded [N.sub.2] associated
to the cell wall components, as % of the total crude protein.

TABLE II
DIGESTION CHARACTERISTICS AND EFFECTIVE DEGRADABILITY OF DRY
MATTER, CRUDE PROTEIN AND NEUTRAL DETERGENT FIBER IN THE
FORAGE OF THE HYBRID NUECES AND FIVE NEW GENOTYPES OF BUFFELGRASS

Concept                          Genotype

               Nueces        PI 1         PI 2        PI 3

EDDM, %       66.3 (a)     62.6 (b)     55.0 (d)    61.5 (b)
a, %          43.3 (a)     37.7 (b)     30.3 (d)    38.8 (b)
b, %          40.7 (a)     42.9 (a)     43.2 (a)    37.4 (a)
c, %/h         3.4 (c)      3.7 (abc)    3.4 (bc)    4.1 (ab)
DDM, ton/ha    3.2 (a)      3.2 (a)      2.1 (a)     2.2 (a)

EDCP, %       70.8 (a)     68.6 (a)     55.3 (c)    59.4 (bc)
a, %          49.7 (a)     46.7 (ab)    30.2 (c)    34.6 (bc)
b, %          37.4 (a)     37.1 (a)     43.6 (a)    40.4 (a)
c, %/h         3.4 (c)      3.8 (abc)    3.5 (bc)    4.2 (ab)
DCP, kg/ha     0.28 (ab)    0.28 (ab)    0.17 (b)    0.16 (b)

EDNDF, %      69.6 (a)     64.5 (c)     58.2 (d)    63.8 (c)
a, %          48.8 (a)     39.5 (c)     37.0 (c)    44.0 (b)
b, %          34.2 (a)     41.0 (a)     37.6 (a)    32.8 (a)
c, %/h         4.1 (a)      4.2 (a)      3.3 (a)     4.0 (a)

Concept              Genotype

                PI 4        PI 5        Mean [+ or -] SE

EDDM, %       62.2 (b)    57.9 (c)     60.9  [+ or -] 0.9
a, %          38.8 (b)    35.3 (c)     37.4  [+ or -] 0.1
b, %          38.1 (a)    38.6 (a)     40.2  [+ or -] 0.8
c, %/h         4.3 (a)     3.8 (abc)    3.8  [+ or -] 0.1
DDM, ton/ha    3.5 (a)     2.4 (a)      2.7  [+ or -] 0.2

EDCP, %       67.2 (ab)   63.9 (ab)    64.2  [+ or -] 1.6
a, %          46.1 (ab)   43.0 (abc)   41.7  [+ or -] 2.2
b, %          34.1 (a)    34.2 (a)     37.8  [+ or -] 1.2
c, %/h         4.4 (a)     4.1 (ab)     3.2  [+ or -] 0.12
DCP, kg/ha     0.33 (a)    0.24 (ab)    0.24 [+ or -] 0.01

EDNDF, %      66.4 (b)    55.4 (e)     63.0  [+ or -] 1.18
a, %          43.8 (b)    31.0 (d)     40.7  [+ or -] 1.42
b, %          42.8 (a)    39.6 (a)     38.0  [+ or -] 1.20
c, %/h         3.4 (a)     4.3 (a)      3.9  [+ or -] 0.18

(abcd) Indicate difference (P<.05) among values in a row.

EDDM: effective degradability of the dry matter; EDCP: effective
degradability of crude protein; EDNDF: effective degradability of
neutral detergent fiber, calculated using a rumen outflow rate of
2.0%/h; a: fraction of DM or CP or NDF (%) lost during washing;
b: fraction of DM or CP or NDF (%) slowly degraded in the rumen
of sheep; c: degradation rate of DM or CP or NDF (%/h); DDM:
digestible dry matter (TDM x EDDM); DCP: digestible crude protein
(TDM x CP x EDCP); SE: standard error.

TABLE III
MACRO AND TRACE MINERAL CONTENT IN THE FORAGE OF THE HYBRID NUECES
AND FIVE NEW GENOTYPES OF BUFFELGRASS

Concept (1)                        Genotype

              Nueces           PI 1          PI 2          PI 3

Ca, g/kg        0.38 (a)      0.38 (a)     0.37 (a)       0.38 (a)
P, g/kg         0.11 (ab)     0.12 (a)     0.10 (ab)      0.10 (ab)
Na, g/kg        0.12 (c)      0.17 (b)     0.12 (c)       0.12 (c)
K, g/kg        24.3 (a)      28.7 (a)     23.7 (a)       21.4 (a)
Mg, g/kg        0.46 (ab)     0.40 (c)     0.44 (abc)     0.42 (bc)
Cu, mg/kg       2.50 (bc)     3.27 (ab)    2.60 (b)       1.49 (c)
Fe, mg/kg     137.6 (a)     172.4 (a)     76.4 (a)      135.0 (a)
Zn, mg/kg      12.3 (d)      18.7 (c)     26.4 (ab)      27.9 (a)
Mn, mg/kg      28.9 (a)      29.9 (a)     29.8 (a)       28.7 (a)
Co, mg/kg       6.8 (a)       6.7 (a)      6.8 (a)        6.8 (a)
Mo, mg/kg       1.9 (a)       1.5 (ab)     1.0 (b)        1.1 (b)

Concept (1)           Genotype

                  PI 4          PI 5         Mean [+ or -] SE

Ca, g/kg        0.37 (a)       0.37 (a)     0.38 [+ or -] 0.002
P, g/kg         0.10 (ab)      0.09 (b)     0.10 [+ or -] 0.003
Na, g/kg        0.24 (a)       0.11 (c)     0.15 [+ or -] 0.01
K, g/kg        25.1 (a)       23.9 (a)      24.5 [+ or -] 1.1
Mg, g/kg        0.43 (abc)     0.48 (a)     0.44 [+ or -] 0.01
Cu, mg/kg       4.26 (a)       2.65 (b)      2.8 [+ or -] 0.2
Fe, mg/kg     131.7 (a)      115.3 (a)     128.1 [+ or -] 9.9
Zn, mg/kg      20.7 (bc)      17.9 (cd)     20.6 [+ or -] 1.5
Mn, mg/kg      42.2 (a)       26.3 (a)      31.0 [+ or -] 1.8
Co, mg/kg       7.0 (a)        6.6 (a)       6.8 [+ or -] 0.1
Mo, mg/kg       1.3 (b)        1.07 (b)      1.3 [+ or -] 0.1

(abcd) Indicate difference (P<.05) among values in a row.

(1) dry matter basis.

TABLE IV
POTENTIAL MINERAL INTAKE OF GROWING CATTLE CONSUMING FORAGE OF THE
HYBRID NUECES AND FIVE NEW GENOTYPES OF BUFFELGRASS

Concept               Potential mineral intake (1)
                               Genotypes

            Nueces    PI 1    PI 2     PI 3     PI 4     PI 5

Ca, g/kg       3.9      3.9     3.8      3.8      3.8      3.8
P, g/kg        1.1      1.3    0.98      1.0      1.0      0.9
Na, g/kg       1.3      1.8     1.2      1.3      2.4      1.1
K, g/kg      247.5    292.9   242.2    218.2    255.5    243.9
Mg, g/kg       4.7      4.1     4.5      4.3      4.4      4.9
Cu, mg/kg     25.6     33.3    26.5     15.2     43.5     27.0
Fe, mg/kg   1403.1   1758.1   779.1   1377.1   1343.4   1176.5
Zn, mg/kg    125.2    190.6   269.5    284.3    211.0    182.0
Mn, mg/kg    295.2    305.3   303.7    292.8    430.2    267.8
Co, mg/kg     69.5     68.0    68.9     69.2     71.8     67.3
Mo, mg/kg     19.3     15.0    10.6     11.6     13.9     10.9

Concept             Requirements

            Required in    Mineral daily
            the diet (2)   Requirements (3)

Ca, g/kg             1.8         18.3
P, g/kg              1.8         18.3
Na, g/kg             1.0         10.2
K, g/kg              6.0         61.2
Mg, g/kg             0.7          7.1
Cu, mg/kg            7.0         71.4
Fe, mg/kg           30.0        306.0
Zn, mg/kg           50.0        510.0
Mn, mg/kg           30.0        306.0
Co, mg/kg            1.8         18.3
Mo, mg/kg            1.8         18.3

(1) Assuming a cow of 400kg with a dry matter intake of 10.2kg
(NRC, 1984), times the concentration of each mineral in the plant
of buffel grass, reported in Table III.

(2,3) Daily requirement (McDowell, 1997) in the dry matter of
the diet of a cow weighing 400kg with a daily mineral intake
of 10.2 kg (NRC, 1996).


ACKNOWLEDGMENTS

The authors acknowledge financial support from CONACYT-SIREYES (Project 2000-60-1006) and Fundacion Produce N.L.

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RESUMEN

Este trabajo evalua y compara la produccion de materia seca (MST), el contenido nutrimental y degradabilidad efectiva de la materia seca (DEMS), proteina cruda (DEPC) y pared celular (DEFDN) de cinco nuevas lineas y un hibrido de pasto buffel en el noreste de Mexico. El consumo potencial de minerales contenidos en los nuevos genotipos por bovinos tambien fue estimado. Todos los pastos se establecieron bajo condiciones de temporal usando un diseno completamente al azar con tres repeticiones. La colecta manual de plantas fue llevada a cabo el 14 nov., 2000, en Nuevo Leon, Mexico. La produccion de MST no fue significativamente diferente entre zacates. Sin embargo, la proteina cruda, pared celular y sus componentes (celulosa, hemicelulosa y lignina) fueron significativamente diferentes entre los pastos evaluados. Asimismo, DEMS, DEPC y DEFDN fueron significativamente diferentes entre pastos. El hibrido Nueces tuvo los valores mas altos para degrabilidad, mientras la linea PI 2 tuvo los valores mas bajos. Al parecer el alto contenido de lignina en los nuevos genotipos pudo haber influido en la baja degradacion de los nutrientes en el rumen de los borregos. Solo K, Fe y Co, en todos los zacates, tuvieron concentraciones suficientes para satisfacer los requerimientos de ganado de carne. Los resultados de produccion de materia seca y dinamica nutricional sugieren que las nuevas lineas PI 1 y PI 4 pueden ser consideradas como buenos substitutos del hibrido Nueces para rumiantes en pastoreo en el noreste de Mexico.

RESUMO

Este trabalho avalia e compara a producao de materia seca (MST), conteudo nutricional e capacidade de degradacao efetiva da materia seca (DEMS), proteina crua (DEPC) e parede celular (DEFDN) de cinco novas lineas e um hibrido de pasto buffel no nordeste do Mexico. O consumo potencial de minerais contidos nos novos genotipos por bovinos tambem foi estimado. Todos os pastos se estabeleceram sob condicoes de temporal usando um desenho completamente ao azar com tres repeticoes. A colheita manual de plantas foi levada adiante em 14 nov., 2000, em Nuevo Leon, Mexico. A producao de MST nao foi significativamente diferente entre pastos. No entanto, a proteina crua, parede celular e seus componentes (celulosa, hemi-celulosa e lignina) foram significativamente diferentes entre os pastos avaliados. Assim mesmo, DEMS, DEPC e DEFDN foram significativamente diferentes entre pastos. A hibrida "Nozes" teve os valores mais altos para degrabilidade, enquanto que a linea PI 2 teve os valores mais baixos. Ao parecer o alto conteudo de lignina nos novos genotipos pode ter influido na baixa degradacao dos nutrientes no rumen dos borregos. So K, Fe e Co, em todos os pastos, tiveram concentracoes suficientes para satisfazer os requerimentos de gado de carne. Os resultados de producao de materia seca e dinamica nutricional sugerem que as novas lineas PI 1 e PI 4 podem ser consideradas como bons substitutos do hibrido Nozes para ruminantes era pastoreio no nordeste do Mexico.

Guillermo Juan Garcia Dessommes. M.Sc. in Ruminal Nutrition. Researcher, Instituto Nacional de Investigaciones Forestales, Agricolas y Pecuarias (INIFAP), Mexico. Doctoral Candidate, Universidad Autonoma de Nuevo Leon (UANL), Mexico. Address: Apartado Postal No 3, General Teran, N. L: CP 67400. Mexico. e-mail: dessommes57@hotmail.com

Roque Gonzalo Ramirez Lozano. D. Sc. in Ruminal Nutrition, UANL. Professor-Researcher, School of Biological Sciences, UANL, Mexico. Address: Apartado Postal, 142, Suc. F, Cd. Univesitaria, San Nicolas de los Garza, N.L., 66451, Mexico. e-mail: roqramir@fcb.uanl.mx.

Rahim Foroughbackhch P. Doctor in Biological Sciences, UANL. Professor-Researcher, Department of Botany, School of Biological Sciences, UANL, Mexico. Address: Pedro de Alba y Manuel Barragan S/N, Cd. Universitaria, San Nicolas de los Garza, N.L., 66451, Mexico.

Rocio Morales Rodriguez. Candidate to M. Sc. in Food Sciences, UANL. Address: Pedro de Alba y Manuel Barragan S/ N, Cd. Universitaria, San Nicolas de los Garza, N.L., 66451, Mexico.

Graciela Garcia Diaz. D. Sc. in Biotechnology, UANL. Professor-Researcher, School of Biological Sciences, UANL, Mexico. Address: Pedro de Alba y Manuel Barragan S/N, Cd. Universitaria, San Nicolas de los Garza, N.L., 66451, Mexico.
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Author:Garcia Dessommes, Guillermo Juan; Ramirez Lozano, Roque Gonzalo; Foroughbackhch P., Rahim; Morales R
Publication:Interciencia
Date:Apr 1, 2003
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