Production of beef cattle grazing on Brachiaria brizantha (Marandu grass)—Arachis pintoi (forage peanut cv. Belomonte) mixtures exceeded that on grass monocultures fertilized with 120 kg N/ha

Mixed grass/legume pastures are an alternative to grass monocultures for increased beef cattle production in tropical climates. The objective of this study was to evaluate the productivity of beef cattle grazing either a mixed pasture of Brachiaria brizantha cv. Marandu grass and Arachis pintoi (forage peanut) cv. Belomonte or a Marandu monoculture, under rotational stocking. Five trials were conducted over a period of nine years in north-eastern Brazil where the sward structure (forage, grass and legume mass) and animal performance were compared for a mixed Marandu grass/forage peanut pasture, and a Marandu grass monoculture with 120 kg N ha⁻¹ y⁻¹. Stocking rate was adjusted to maintain forage allowance at 4% body weight/day. A block design was used with four replicates, and warm and cool seasons within each trial were considered, using repeated measurements over time. In the warm season, the forage mass in the mixed pastures was 17% greater than in the monoculture (p = .049), and the stocking rate, average daily gain and liveweight gain per ha were 16.4%, 20.0% and 28.7% greater (p = .004, p < .001 and p < .001 respectively). The average daily gain showed a positive linear relationship with the legume proportion in the sward (p < .001). The mixed forage peanut/Marandu pasture sustained significantly greater beef cattle production (789 kg ha⁻¹ y⁻¹) compared to the N-fertilized grass monoculture (655 kg ha⁻¹ y⁻¹). Appropriately managed, mixed pastures of forage peanut/Brachiaria pastures are sustainable and have high potential for use in the humid tropics.     

Liveweight gain of beef cattle in Brachiaria brizantha pastures and mixtures with Stylosanthes guianensis in the Brazilian savannah

The use of stylosanthes in mixed grass-legume pastures may minimize the decline in forage quality and quantity that occurs in monoculture grass pastures, even though the availability of commercial cultivars in Brazil is still limited. The objective of the study was to evaluate the liveweight (LW) gain of young Nellore bulls in a mixed pasture of Brachiaria brizantha (cv. Paiaguás) with the latest release Stylosanthes guianensis cv. Bela. The study was conducted in Planaltina, FD, Brazil, from September to August in two consecutive years, right after seeding. The experimental design was a randomized complete block design with two treatments (mixed or monoculture Paiaguás pastures) and three replicates. The average daily gain (ADG) was on average greater in mixed pastures (0.436 vs. 0.350 kg head⁻¹ day⁻¹ in mixed and grass pastures respectively), particularly in the dry period (0.344 vs. 0.183 kg head⁻¹ day⁻¹). The benefit of mixed over monoculture grass pastures throughout the year was 22 kg LW/head and 55 kg LW/ha. The presence of stylosanthes increased the crude protein (CP) concentration in mixed pastures (120 g/kg) when compared to monoculture grass pastures (109 g/kg), probably influencing the ADG of bulls. The increase of liveweight gain, predominantly in the dry season, makes the high-protein stylosanthes cv. Bela an alternative to buffer the seasonal deficit of forage quality in newly seeded grass pastures.     

Effect of Phenobarbitone Treatment Against Signal Grass (Brachiaria decumbens) Toxicity in Sheep

The effect of phenobarbitone against signal grass (Brachiaria decumbens) toxicity was studied in 26 male crossbred sheep. Grazing on signal grass significantly decreased the concentration of cytochrome P-450 and the activity of drug metabolizing enzymes, viz. aminopyrine-N-demethylase, aniline-4-hydroxylase, UDP- glucuronyltransferase and glutathione-S-transferase in liver and kidneys of affected sheep.Oral administration of phenobarbitone (30 mg/kg body weight) for five consecutive days before grazing on B. decumbens pasture, and thereafter, for three consecutive days every two weeks, resulted in significant increases in hepatic and renal activities of drug-metabolizing enzymes. The induction of drug metabolizing activity in sheep grazing on signal grass group was found to be lower than in animals given phenobarbitone alone. Induction by phenobarbitone provided a degree of protection against the toxic effects of B. decumbens as indicated by the delay in the appearance of signs of toxicity. Furthermore, these were much milder compared to those in the sheep not treated with phenobarbitone. The present study suggests that phenobarbitone-type cytochrome P-450 isoenzyme-induction may increase resistance against signal grass (B. decumbens) toxicity in sheep.     

Morphological and physiological responses and the recovery ability of Paspalum accessions to water deficit and waterlogging

Limited knowledge about the agronomic potential of Paspalum species from the Americas hinders their use in pastures. The response mechanisms to water deficit and waterlogging were studied in five accessions of Paspalum sp. (P. regnellii cv. BRS Guará and BGP 397, P. conspersum BGP 402 and P. malacophyllum BGP 289 and BGP 293) and Urochloa brizantha cv. Marandu. Morphological and physiological traits at the end of the stress and after the recovery period were measured. All Paspalum accessions, especially BGP 289, BGP 402 and BGP 397, and also cv. Marandu, showed survival mechanisms to water deficit. BRS Guará showed adaptive features to waterlogging, although had with a low survival rate to water deficit. Under waterlogging, BGP 289 and cv. Marandu showed reduced growth, and after the recovery period, they presented low plant survival and root recovery. Although growth of BGP 293 was reduced during waterlogging, it presented high tiller survival rate. BGP 293, BGP 402 and BGP 397 showed adaptive potential strategies for waterlogging and water deficit. There is genetic variability among the evaluated accessions for water deficit and waterlogging stresses, suggesting that they may be used per se or as progenitors in crosses with other genotypes in breeding programmes.     

Canopy characteristics and tillering dynamics of Marandu palisade grass pastures in the rainy–dry transition season

The objective of this study was to evaluate the effect of pasture management during the rainy–dry transition season in Jaboticabal, Brazil, on the structural and tillering characteristics of Marandu palisade grass. The treatments were as follows: 15 cm sward height in the rainy season and ungrazed in the rainy–dry transition season (15/0); 25 cm sward height during the rainy season and fixed stocking rate of 2·5 AU ha^?1 during the rainy–dry transition season (25/2·5); and 35 cm sward height in the rainy season and fixed stocking rate of 2·5 AU ha^?1 in the rainy–dry transition season (35/2·5). There were more herbage mass, stem and dead herbage mass in treatments 25/2·5 and 35/2·5 than 15/0. Tiller appearance rate was greater in treatment 15/0 and tiller mortality rate was higher in treatment 35/2·5 compared to treatment 15/0. Tiller population stability index was 1 in treatment 15/0 and lower in treatment 35/2·5. Although treatment 15/0 showed favourable structural and tillering characteristics, it also has the lowest herbage mass. Treatment 25/2·5 can be regarded as an adequate management strategy for Marandu palisade grass, since it has similar herbage mass and better tillering characteristics than treatment 35/2·5.     

臂形草内生菌特异DNA片段的克隆及其分子鉴定

进行了臂形草内生菌特异DNA片段的克隆及分子鉴定方法的研究。从5个臂形草品种分离的5个内生菌纯培养特中，提取基因组DNA，通过140条随机引物的RAPD分析，引物OPAK10扩增出1条约500bp的共有PCR谱带。此DNA片段命名为BE1。对BE1进行分离、纯化，经点杂交证实BE1为臂形草内生菌特异DNA片段。进一步将BE1片段进行回收、克隆和DNA序列分析。BE1在基因库中进行序列分析，未发现相关同源片段。臂形草内生菌特异DNA片段的获得，为建立一种准确、快速检测臂形草内生菌及特异内生菌方法奠定了分子生物学基础。     

A simple method for measuring tiller volume of grasses

A simple method for measuring tiller volume of grasses is described. The equipment, based on the communicant pipe principle, was built using a PVC pipe linked to a laboratory volumetric pipette. The results showed a high degree of consistency and were similar to empirical results published in the literature, indicating that tiller volume of grasses can be easily measured with this technique.     

Chromosome number and microsporogenesis in a pentaploid accession of Brachiaria brizantha (Gramineae)

Chromosome number, microsporogenesis and mode of reproduction are described for an accession of Brachiaria brizantha, a grass of African origin. Cytological analysis revealed that the accession BRA005886 is pentaploid (2n = 5x = 45), with a base number of x = 9. Multivalent chromosome associations, from tri‐ to pentavalents, were recorded in diakinesis, and the further meiotic behaviour was highly irregular as well. Most abnormalities were related to irregular chromosome segregation commonly found in polyploids. Micronuclei were observed following telophases I and II. Some micronuclei near the cell wall were released as microcytes, whereas others remained in the tetrad. Other meiotic abnormalities, such as cell fusion and the absence of cytokinesis causing the formation of dyads and triads were also recorded. Binucleate microspores and 2n microspores resulting from nucleus restitution were observed among the normal ones. Limitations of this accession for use in hybridization programmes are discussed.     

Chromosome numbers and microsporogenesis in Brachiaria brizantha (Gramineae)

The genus Brachiaria, native to the African tropical savannas, has achieved significance as a pasture grass in many tropical and subtropical countries, including Brazil. Many species and accessions are polyploid and apomictic, which complicates the improvement of breeding stocks through hybridization. In support of breeding programs, cytogenetic characterization, including chromosome counts and evaluation of the meiotic behavior in the accessions of the Brachiaria has been undertaken at the Embrapa Beef Cattle Center. In this study, 22 accessions of B. brizantha were analyzed of which one was found to be diploid (2n = 2x = 18), 18 were tetraploid (2n = 4x = 36) and three were hexaploid (2n = 6x = 54). The meiotic chromosome behavior was slightly irregular in the diploid and in some tetraploid accessions, and highly irregular in most tetra- and hexaploid accessions. Meiotic abnormalities were those common to polyploidy, i.e., multivalent chromosome association at diakinesis and irregular chromosome segregation leading to micronuclei formation in the tetrad stage. Low frequencies of multivalent chromosome associations among polyploids suggest that they may be segmental allopolyploids. This revised version was published online in August 2006 with corrections to the Cover Date.