CHEMICAL COMPOSITION AND RUMEN DIGESTION OF FORAGEFROM KLEINGRASS (Panicum coloratum)

Roque Gonzalo Ramírez Lozano, Humberto González Rodríguez and Guillermo García Dessommes

Roque Gonzalo Ramírez Lozano. Doctor of Science in Ruminant Nutrition, Universidad Autónoma de Nuevo León (UANL). Professor-Researcher, Departamento de Alimentos, Facultad de Ciencias Biológicas, UANL. Address: Apartado Postal, 142, Suc. F, Cd. Universitaria, San Nicolás de los Garza, N.L., 66451, México. e-mail: roqramir@fcb.uanl.mx.

Humberto González Rodríguez. Doctor of Science in Plant Physiology, UANL. Professor-Researcher, Facultad de Ciencias Forestales, UANL.

Guillermo García Dessommes. M. C. in Ruminant Nutrition and Researcher, Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias (INIFAP). Doctorate Candidate in Sciences Nutrition, UANL.

Summary

This study evaluated and compared, seasonally, the nutrient content and effective degradability of dry matter (EDDM), crude protein (EDCP) and neutral detergent fiber (EDNDF) of the total plant, leaves and stems of kleingrass growing in Northeastern Mexico. Potential intake by cattle of minerals contained in the whole plant of kleingrass was also estimated. Plants were hand harvested in each season, in a 20ha rain fed pasture. Values of crude protein, Ca, P, K, Mg, Na, Fe, Cu, Zn, Mn, EDDM, EDCP and EDNDF were significantly higher in spring than in other seasons. Conversely, cell wall and its components (cellulose, hemicellulose and lignin) were significantly lower in spring than in other seasons. Leaves resulted with significantly higher chemical composition and effective degradability of nutrients than stems. Whole plant concentrations of Ca, K and Fe (in all seasons); of Mg (except in winter); and of Zn and Mn (except in winter and summer) were sufficient to satisfy growing cattle requirements of these minerals. However, P, Na and Cu concentrations were low for cattle needs in all seasons. In this study, leaves had better nutritional quality than stems; in addition, rainfall and plant maturity influenced the nutritive quality and effective degradability of kleingrass.

KEYWORDS / Effective Degradability / Kleingrass / Mineral Potential Intake / Ruminants /

Resumen

El estudio evaluó y comparó, estacionalmente, el contenido nutrimental y degradabilidad efectiva de la materia seca (DEMS), proteína cruda (DEPC) y pared celular (DEFDN) de la planta completa, hojas y tallos del zacate klein, sembrado en el noreste de México. El consumo potencial de minerales por bovinos, contenidos en la planta completa del zacate klein, fue también estimado. La colecta manual de plantas fue llevada a cabo en cada estación, en una pradera no irrigada de aproximadamente 20ha. Los valores de proteína cruda, Ca, P, Mg, K, Na, Fe, Zn, Cu, Mn, DEMS, DEPC, DEFDN fueron significativamente más elevados en primavera que en otras estaciones. Contrariamente, la pared celular y sus componentes (celulosa, hemicelulosa y lignina) fueron significativamente más bajos en primavera que en otras estaciones. Las hojas del zacate klein resultaron con mayor calidad nutritiva y degradabilidad efectiva que los tallos. En el zacate klein, el contenido total de Ca, K y Fe (en todas las estaciones del año), de Mg (excepto en invierno), y de Zn y Mn (excepto en invierno y verano) fue suficiente para satisfacer los requerimientos de bovinos en crecimiento; sin embargo, P, Na y Cu fueron deficientes en todas las estaciones. En este estudio las hojas tuvieron mejor calidad nutritiva que los tallos; además, la precipitación y el estado de la madurez de la planta tuvieron influencia sobre la calidad nutritiva y degradabilidad ruminal del zacate klein.

Resumo

O estudo avaliou e comparou, estacionalmente, o conteúdo nutrimental e degradabilidade efetiva da matéria seca (DEMS), proteína crua (DEPC) e parede celular (DEFDN) da planta completa, folhas e caules do zacate klein, semeado no noroeste do México. O consumo potencial de minerais por bovinos, contidos na planta completa do zacate klein, foi também estimado. A colheita manual de plantas foi realizada em cada estação, numa pradera não irrigada de aproximadamente 20ha. os valores de proteína crua, Ca, P, Mg, K, Na, Fe, Zn, Cu, Mn, DEMS, DEPC, DEFDN foram significativamente mais elevados na primavera que em outras estações. Contrariamente, a parede celular e seus componentes (celulosa, hemicelulosa, lignina) foram significativamente mais baixos na primavera que em outras estações. As folhas do zacate klein resultaram com maior qualidade nutritiva e degradabilidade efetiva que os caules. No zacate klein, o conteúdo total de Ca, K e Fe (em todas as estações do ano), de Mg (excepto no inverno), e de Zn e Mn (excepto no inverno e verão) foi suficiente para satisfazer os requerimentos de bovinos em crescimento; no entanto, P, Na e Cu foram deficientes em todas as estações. Neste estudo as folhas tiveram melhor qualidade nutritiva que os caules; além disso, a precipitação e o estado da madurez da planta tiveram influência sobre a qualidade nutritiva e degradabilidade ruminal do zacate klein.

Received: 07/10/2002. Modified: 10/29/2002. Accepted: 12/11/2202

Introduction

Effective degradability and rate and extent of digestion in the rumen are important characteristics of forage digestion in ruminants. Such characteristics can be used to predict the nutritive value more accurately and compare the utility of forages in the diets for ruminants (Ørskov, 1991). Grasses are important sources of organic and inorganic nutrients for ruminants; however, under some circumstances, they can be deficient in one or more of these nutrients. Minerals are required to meet the animal needs for optimum growth and health (Spears, 1994) because minerals are essential nutrients for all kinds of animals and in this way influence animal performance (McDowell, 1997).

Kleingrass (Panicum coloratum) is a perennial grass of warm climates, native of Africa. Depending on soil fertility and rainfall, dry matter production varies from 4 to 7 tons/ha/year. It can efficiently produce with 500mm of annual rainfall and it is highly palatable. In Texas, USA, its crude protein content varies from a low value of 7% in winter to a high value of 13% in spring (Polk et al., 1976). In Argentina, the effective degradability of dry matter of kleingrass in the rumen varied depending on the part of the plant; leaves were more degraded than stems (Stritzler et al., 1996). Apparently, kleingrass is an excellent complement for the short-cycle grazing systems and has been successfully introduced in Northern Mexico (Velázquez-Caudillo, 1997). However, its seasonal nutritive value and ruminal degradability characteristics have not been studied.

Different parts of the plant differ in nutritional qualities. In grasses, leaves generally have better nutritional quality than stems (Ramírez et al., 2001a, b, 2002). Because ruminants rarely consume the total plant, analyses of only one fraction of the plant may underestimate the nutritive value of forages, when they are consumed by the animal (Stritzler et al., 1996).

The aim of this study was to determine and estimate, seasonally, the nutritive value and effective degradability in the rumen of the total plant, leaves and stems of kleingrass that grow in Northeastern Mexico.

Materials and Methods

The research was carried out at the Experimental Production Unit of the Universidad Autonoma de Nuevo León, Linares, N.L., Mexico, located at 24º47´N and 99º32W, at an altitude of 350masl. The climate is typically semitropical and semiarid, with a warm summer. The main and most common type of vegetation is known as the Tamaulipan Thornscrub or subtropical Thornscrub woodlands. The dominant soils are deep, dark-gray, lime-clay Vertisols, which are the result of alluvial processes. This type of soils is characterized by high Ca carbonate (pH= 7.5 to 8.5) and relatively low organic matter content (Foroughbachkch, 1992).

During fall (September 26, 1996), winter (January 30, 1997), spring (April 21, 1997) and summer (July 22, 1997), plants were hand-harvested from a 10ha kleingrass (Panicum coloratum L. Pers) pasture. In each season ten sites were randomly selected for plant collection. After harvest, plants were separated into leaves and stems and partial dry matter was determined at 55ºC in an oven for 72h. After drying, samples were ground in a Wiley mill (1mm screen) and stored. In each season, leaves and stems from plants from the ten sites of collection were bulked separately and divided into four samples that were subjected to chemical analysis and in situ disappearance studies.

Samples were analyzed for dry matter (DM), organic matter, crude protein (CP), ash, acid detergent lignin (ADL; AOAC, 1990), neutral detergent fiber (NDF) and acid detergent fiber (ADF; Goering and Van Soest, 1970). Hemicellulose (NDF-ADF) and cellulose (ADF-ADL) were estimated by difference. Mineral content was estimated by incinerating the samples in a muffle furnace at 550°C for 4h. Ashes were digested in a solution containing HCl and HNO3, using the wet digestion technique (Díaz-Romeau and Hunter, 1978). Concentrations of Ca, Mg, K, Na, Fe, Mn, Zn and Cu were estimated using an atomic absorption spectrophotometer. The P content was determined colorimetrically (AOAC, 1990).

The rate and extent of fermentation in the rumen of DM, CP and NDF from kleingrass were measured using twelve rumen cannulated Pelibuey x Rambouillet sheep weighing 45.2 ±2.3kg. In each season, four sheep were used to evaluate each plant part. Animals were fed with alfalfa hay ad libitum two weeks before beginning the in situ trial and throughout the experiment. Sheep used in this study were maintained and treated according with international regulations of animal care. Ground (4g) samples were placed in nylon bags (5 x 10cm, 53mm pore size) and suspended in the ventral sac of the rumen of each sheep. Bags were incubated in each sheep for 4, 8, 12, 24, 36 and 48 hours. Upon removal, from the rumen, bags were washed in cold water. Zero time disappearance was obtained by washing unincubated bags in a similar fashion. Bags were dried at 60ºC in an oven during 48h. Weight loss of DM, CP and NDF was recorded.

In order to estimate the non-linear characteristics of in situ disappearance of DM, CP or NDF from nylon bags in each incubation period, equation (1) from Ørskov and McDonald (1979) was used:

p = a + b (1- e-ct)    (1)

where p: disappearance rate at time t; a: an intercept representing the portion of DM or CP or NDF solubilized 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 effective degradability of DM (EDDM), CP (EDCP) or NDF (EDNDF) = (a+b)c/(c+k)(e-(ct)LT) was calculated using the Neway computer program (McDonald, 1981); where 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 3%/hour.

The chemical composition, nonlinear parameters of digestibility, and EDDM and EDCP and EDNDF were statistically analyzed, using a 4x3 factorial experiment, where seasons represented Factor A and plant parts Factor B. Seasonal means were compared using the Tukey test (P<0.05). Simple correlation analysis was performed to estimate the influence of chemical composition, rainfall, temperature, and EDDM, EDCP and EDNDF (Steel and Torrie, 1980). All the statistical procedures were performed using the Statistical Package for Social Sciences, version 9.0 (SPSS, 1999).

Results and Discussion

The CP content of kleingrass was significantly different among seasons. In spring, CP was highest and in winter lowest. Leaves resulted with higher CP content than stems (Table I). Velásquez-Caudillo (1997) also found that the CP of kleingrass that grows in Northern Mexico, was highest in spring (14.9%) and lowest in winter (7.0%). In addition, Polk et al. (1976) reported that the CP in leaves of kleingrass that grows in three sites of Texas, USA, was highest during spring (13%) and lowest in winter (9%). In South America, Stritzler et al. (1996) reported that the CP of kleingrass that grows in Las Pampas, Argentina, was higher in leaves than in stems.

Cell wall NDF and its components (cellulose, hemicellulose, ADL and insoluble ashes) were significantly different among seasons. In general, during spring the percentage of NDF in kleingrass was lowest and in winter it was highest. In winter, plant maturity and ADL were highest (Table I). With exception of hemicellulose and insoluble ashes, other cell wall components were lower in leaves than in stems (Table I). Values of cell wall similar to those found in this study have been reported by Velásquez-Caudillo (1997). Moreover, Stritzler et al. (1996) mentioned that leaves of kleingrass growing in Las Pampas, Argentina, had lower cell wall content than stems. Roquette et al. (1974) also reported that NDF content in three varieties of kleingrass growing in Texas, USA, increased as plant maturity increased. Besides, Pitman et al. (1983) and Pitman and Holt (1982) concluded that because of the increased humidity stress, cell wall content and degree of lignification of kleingrass increased.

The EDDM, EDCP and EDNDF were significantly different among seasons. In general, in spring DM, CP and NDF of kleingrass were fermented to a greater extent in the rumen of sheep than in other seasons. During spring, kleingrass had the highest CP and the lowest NDF contents; however, in winter, when kleingrass had the lowest CP and the highest NDF contents, ruminal degradability of nutrient was lowest (Table I). Moreover, CP positively influenced EDNDF (r=0.48, P<0.001) and, NDF negatively affected EDDM, EDCP and EDNDF (r=-0.46, P<0.001; r=-0.28, P<0.01; r=-0.80, P<0.001, respectively) The EDDM, EDCP and EDNDF values were higher in leaves than in stems (Table I). Stritzler et al. (1996) when evaluated the whole plant, leaves and stems of kleingrass, also found that leaves were superior in rumen DM degradability than stems (45.4; 54.7 and 43.6%, respectively).

It seems that rainfall and lignification had an effect on the chemical composition and rumen degradability of kleingrass. During the spring season, when rainfall was highest, EDDM and EDCP increased (Table II). Conversely, in spring, when degree of lignification was lowest, EDDM, EDCP and EDNDF also increased. These effects have already been reported in the nutrients in forage of common buffelgrass (Ramírez et al., 2001a) and in the hybrid Nueces buffelgrass (Ramírez et al., 2001b) that grows in Northeastern Mexico. These authors reported that when rainfall was high, effective degradability of nutrients in grasses was also high.

Concentrations of all minerals in kleingrass were significantly different among seasons. In general, minerals were highest in spring and lowest in winter (Table III). Apparently, rainfall would have influenced the mineral content of kleingrass, because during spring, when rainfall was highest (417mm), mineral content was also highest. Seasonality of mineral content in grasses has been previously reported by Ramírez et al. (2002) who found that mineral content of common buffelgrass (Cenchrus ciliaris), growing in Northeastern Mexico was highest during summer, when rainfall was highest.

In this study, all minerals were higher in leaves than in stems (Table III). This confirms previous reports that stated that plant parts differ in quality; leaves have more nutritive quality than stems (McBee and Miller, 1990; Stritzler et al., 1996; Ramírez et al., 2002). Moreover, Velásquez-Caudillo (1997) reported that Ca and P contents of kleingrass that grows in Sonora, Mexico, varied seasonally, with Ca contents of 2.5, 5.0, 3.4 and 3.0g/kg in spring, summer, autumn and winter, respectively. P concentration also varied among seasons (2.2, 1.4, 2.0 and 1.0g/kg, respectively). These Ca and P concentrations are comparable to those reported in the whole plant of this study.

Table IV shows data of potential mineral intake by a 400kg cow, assuming a daily intake of 10.2kg DM of the total kleingrass plant, multiplying it by the respective amount of each mineral that appears in Table I. The potential intake of Ca, Mg (except in winter), K, Mn (except in winter and summer), Fe and Zn (except in winter and summer) would be sufficient to meet the requirements of these minerals in all seasons, for a growing cow of 400kg grazing kleingrass in Northeastern Mexico. However, in all seasons, P, Na and Cu were deficient. Deficiencies of P and Na have been previously reported and they occur in many grass species that grow in warm climates (McDowell, 1997). Moreover, Minson (1990) reported that Na concentrations are in a range of 5.4 to 15.3g/kg DM of P. coloratum and of 1.2 to 5.7g/kg DM in P. maximum Walt. Thus, to obtain an optimal productivity of beef cattle grazing kleingrass in Northeastern Mexico, it has to be supplemented, through out year, with P, Na and Cu, with Mg during winter and during winter and summer with Mn and Zn.

Conclusions

Rainfall and plant maturity influenced the chemical composition, rumen degradability and mineral content of kleingrass. During spring, rainfall and CP content of kleingrass were highest and cell wall material was lowest. These facts may have positively influenced rumen degradability of DM, CP and NDF in spring. Moreover, the potential mineral intake of growing cattle was higher in spring than in other seasons. Minerals such as Ca, K, Mg and Fe in the total plant of kleingrass resulted sufficient, in all seasons, to satisfy the requirements of growing cattle. However, P, Na, Cu, Mn and Zn were deficient in one or more seasons. Leaves had higher nutritional quality than stems. Thus, quality of common kleingrass might be improved when plants are managed or bred to have a greater leaf:stem ratio. Meanwhile, cattle grazing only kleingrass pastures in Northeastern Mexico may be supplemented, in all seasons, with P, Na and Cu and, in spring and autumn with Mn and Zn, for optimal productivity of growing cattle.

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