Two grazing trials and a feedlot trial were conducted with crossbred lambs to evaluate 'Quickstand' bermudagrass (Cynodon dactylon [L.] Pers.) in a cool temperate environment. Four stocking rates and two N fertilization rates (4 x 2 factorial) were replicated three times on .11-ha paddocks. Paddocks were continuously stocked with two, four, six, or eight lambs (light, moderate, heavy, and very heavy stocking rate, respectively) in grazing trial 1. Stocking rates were increased to 4, 8, 12, or 16 lambs per paddock, respectively, in grazing trial 2. In both grazing trials, paddocks were fertilized with 114 (low N) or 340 (high N) kg N ha-1yr-1 in split applications. / Master of Science

Three experiments were conducted to study the effects of dietary potassium intake on magnesium metabolism. In experiment 1, 24 wether lambs were used in two metabolism trials to determine the minimum level of potassium that depresses magnesium absorption. Two magnesium levels (.1 and .2%) were fed with four levels of potassium (.6, 1.2, 2.4 and 4.8%) in a 2 x 4 factorial arrangement of treatments. Each trial consisted of a 10-day preliminary period followed by a 10-day collection period. Greater amounts (P<.05) of magnesium were absorbed and retained when animals were fed the high level of magnesium (.2%). Increasing the level of potassium in the diet increased (P<.05) fecal magnesium excretion. Magnesium absorption decreased linearly with increasing levels of potassium. The greatest depression in magnesium absorption occurred when the potassium level was increased from 1.2 to 2.4%. A further large decrease in absorption occurred when the potassium level was increased from 2.4 to 4.8%. Serum magnesium was depressed when higher levels of potassium were fed. Potassium absorption was not affected by level of dietary magnesium, but increased (P<.05) with increasing levels of dietary potassium. In experiment 2, two metabolism trials were conducted with 18 wether lambs, equipped with abomasal and ileal cannulae, in a 2 x 3 factorial arrangement. Two levels of magnesium (.1 and .2%) and three levels of potassium (.6, 2.4, and 4.8%) were used. Chromic oxide was used as an indicator to determine digesta flow. Each trial consisted of a 10-day preliminary period, a 7-day collection of feed, feces and urine, and a 6-day sampling of feed, abomasal and ileal fluid and feces. Magnesium was absorbed mainly prior to reaching the small intestine, followed by a low net absorption in the large intestine. Increasinq potassium level resulted in a linear decrease in magnesium absorption. Preintestinal magnesium absorption decreased (P<.05) with each increase in dietary potassium. Large amounts of magnesium flowed into the small and large intestines and was excreted in the feces when higher levels of potassium were fed. Lambs fed the high level of magnesium (.2%) absorbed larger amounts of magnesium from the stomach. Magnesium absorbed, expressed as a percent of intake, was not affected by level of magnesium. Experiment 3 consisted of three metabolism trials with six Angus x Simmental steer calves, per trial, equipped with abomasal and ileal cannulae. Steers were fed .1% magnesium and three levels of potassium, .6, 2.4 and 4.8%. Procedures were similar to those used in Experiment 2. Magnesium absorption decreased linearly (P<.05) when high levels of potassium were fed. The primary site of magnesium absorption was the preintestinal region, followed by a net secretion into the small and large intestines. Preintestinal magnesium absorption was decreased approximately 50% when steers were fed 4.8% potassium. Small amounts of magnesium tended to be secreted into the small intestine when the high level of potassium was fed. As observed in experiment 1, serum magnesium levels were depressed when increasing amounts of potassium were fed. Potassium absorption increased with increasing levels of dietary potassium. The effect of high dietary potassium on magnesium absorption was similar to those reported in experiments 1 and 2 with sheep. / Ph. D.

The effects of three fertilization rates of N (0, 112 and 224 kg/ha) as ammonium nitrate and S (0, 34, and 67 kg/ha) as calcium sulphate on yield, chemical composition, digestibility and palatability of orchardgrass (Dactylis glomerata L.) , were studied in a field experiment. Treatments were applied in a randomized block design with a 3x3 factorial arrangement of treatments with four replications. Hay was harvested on 18 Aug. 1982 and fed to sheep in metabolism trials. One half of the initial amount of fertilizer was reapplied and forage was stockpiled. Stockpiled growth was ensiled on 6 Nov. 1982 and was fed to sheep in palatability trials. Fertilizer was reapplied at the initial rates on 27 Apr. 1983 and yield and mineral concentrations were determined on 6 June 1983. Dry matter yield increased in response to N (P<0.01). Nitrogen fertilization decreased NDF (P<0.05) ADF, cellulose (P<0.01) and total S (P<0.01) and increased nitrate-N (P<0.01) in hay and stockpiled growth. In stockpiled growth S increased ADF ( P<0.05) and cellulose quadratically ( P<0.001) at the 34 kg/ha rate. Sulphur increased ( P<0.05) No₃-N in hay but decreased (P<0.05) it in stockpiled growth. The N:S ratio was increased (P<0.01) by N fertilization and decreased (P<0.05) by S fertilization. Nitrogen and S had a quadratic effect (P<0.0001) on lactic acid and water-soluble carbohydrates in silage. Digestibility or palatability of silage was not influenced by N or S. / Master of Science

The effects of red clover (Trifolium pratense, L.), three levels of N (0, 224 and 448 kg•ha⁻1•yr⁻1, as a split application) and two levels of S (0 and 34 kg•ha⁻1•yr ) on the chemical composition and dry matter digestibility of an orchardgrass (Dactylis glomerata, L.) sward were studied. The treatments were replicated three times in a randomized block design with a split-plot arrangement of treatments. Crude protein content, in vitro dry matter digestibility and dry matter yield were increased (P<. 01) with increasing levels of N. Increasing levels of N decreased (P<.05) S content of orchardgrass. The inclusion of red clover did not have any significant effect on the components analyzed, probably due to a low proportion of red clover (approximately 8%) in the mixed sward. Application of S increased ( P<.05) the S content of orchardgrass and decreased N-to-S ratio at all levels of N application. Application of S increased (P<.05) the crude protein and in vitro dry matter digestibility, whereas neutral detergent fiber, lignin and hemicellulose were decreased (P<. 05). Nitrogen fertilization had a quadratic effect (P<.05) on in vivo digestibility of dry matter, acid detergent fiber and hemicellulose and a linear effect (P<.001) on apparent digestibility of crude protein. Inclusion of red clover increased (P<.01) in vivo digestibility of dry matter and hemicellulose, and decreased (P<.01) digestibility of acid detergent fiber and lignin. Application of S had no direct effect on in vivo digestibility of orchardgrass. A linear interaction (P<.01) between N and S was observed for dry matter and crude protein digestibility. Rumen fluid ammonia-N was increased (P<.05) and butyric acid concentration was decreased (P<.05) linearly by N fertilization. / Master of Science

No description available.

Bermudagrass (<i>Cynodon</i> spp.), when cultured at the northern limit of adaptation for semitropical grasses, is exposed seasonally to temperatures low enough to limit growth and turf quality. Research was conducted to investigate the influence of foliar iron and cytokinin applications on bermudagrass growth during fall and spring. The relationship of photosynthesis, respiration, and nonstructural carbohydrate composition to chilling temperatures was also studied. Foliar applications of Fe in late-summer and fall extended bermudagrass performance during low temperature periods of fall. Frequent Fe applications aided the retention of green bermudagrass turf during prolonged exposure to chilling temperatures. Iron applied the previous season stimulated post-dormancy recovery. Benzyladenine (BA) applied alone was not as effective as Fe for promoting green bermudagrass color retention during fall and BA had few effects on spring growth when applied the previous season. Applications of BA in conjunction with Fe were beneficial for retention of green bermudagrass color during late fall when clear plastic covers were used to prevent frost injury. A 6- to 8-week longer bermudagrass growing season occurred when clear plastic covers were used to prevent frost injury. Iron and BA did not significantly affect the total nonstructural carbohydrate (TNC) levels in Midiron bermudagrass rhizomes and stolons at the onset of dormancy in field studies. Midiron bermudagrass had higher photosynthetic and respiration rates than Tifgreen bermudagrass after 4 days exposure to chilling (10/7°C day/night) temperatures in controlled environment studies. Midiron recovered higher photosynthetic rates than Tifgreen when returned to a warm (30°C) environment after exposure to chilling temperatures. The TNC in leaves of Midiron and Tifgreen increased 88 and 160%, respectively, during 5 days at chilling temperatures. The inability to transport carbohydrate from and the subsequent accumulation of high photoassimilate levels in leaves was associated with the inability of bermudagrass to fully recover high photosynthetic rates following chilling. Reduced respiratory activity was apparently responsible for the accumulation of high TNC levels in leaves. In contrast to photosynthesis, respiration was reversibly inhibited by short term exposure of bermudagrass to chilling temperatures. Rapid recovery of high respiratory activity may be important for maintenance of aesthetically pleasing bermudagrass turf following chilling. Foliar applied Fe or BA generally caused darker green Midiron and Tifgreen turf after exposure to chilling temperatures in a controlled environment, although the enhancement of physiological activity differed with chemical applied and cultivar. Iron stimulated recovery of photosynthetic and respiratory activity in both cultivars after exposure to chilling temperatures. However, during chilling Midiron CO₂ exchange was more responsive to Fe applications. Benzyladenine increased photosynthesis in Tifgreen but not in Midiron and did not significantly affect respiration in either cultivar. Neither Fe nor BA had a consistent effect on TNC levels in bermudagrass leaves, rhizomes, or stolons. These investigations indicate that cultivar selection may play a major role in determining turf quality at chilling temperatures. Iron may modify bermudagrass physiology and enhance performance of bermudagrass exposed to chilling temperatures. / Ph. D. / incomplete_metadata

Five crossbred heifers were slaughtered at different times and rumen and omasum tissues were removed: The epithelium was separated from the muscle layer and mounted in parabiotic chambers. The tissues were incubated for 2 h in buffer at 39 C and aerated continuously in 95% O₂ 5% CO₂ . The buffers were similar to those which have been used previously in mineral transport studies, but were modified by varying the levels of Mg and K while keeping the osmolarity constant. Potassium was included in the buffers on the mucosal side in appropriate ratios to Mg to correspond to the K: Mg in diets fed to ruminants which would contain .1% Mg and .6, 2.4 and 4.8% K, (low, medium and high, respectively). A fourth buffer which contained physiological concentrations of Kand Mg, was placed on the serosal side of the parabiotic chamber. Flow of Mg was calculated by: F = C₁V₁ - C₀V₀ / AΔt where C₁ = final concentration, C₀ = original concentration, V₁ = final volume, V₀ = original volume, Δt = incubation time, A = area of the tissue exposed to the buffer, and F = flow of Mg (mg/cm²/h). Blanks were included which contained physiological levels of Mg on both side of the chamber to adjust for tissue effects. Magnesium transport tended to be 10 times greater through the rumen than the omasum. This indicates that the rumen is the primary site of Mg absorption in cattle. Potassium tended to depress Mg transport across both tissues. This technique has only limited application in mineral research. / M.S.

Anopheles gambiae sensu lato mosquitoes are among the dominant malaria vectors in sub-Saharan Africa. However, not much is known about the oviposition behaviour of these species necessary for the development of malaria vector control strategies. With the aim of investigating cues associated with selected oviposition sites, artificial oviposition sites- ponds (soil mixed with water) were set-up in an open field at Mbita, Western Kenya in 2012 and 2013. Ponds were allowed to be colonized by wild An. gambiae s.l.. The numbers of Anopheles early instar larvae were counted and used as a proxy for oviposition preference. Water samples were then analysed for physicochemical, bacterial and chemical profiles. The bacterial profiles were analysed using denaturing gradient gel electrophoresis (DGGE) and the chemical profiles with gas chromatography-mass spectrometry (GC-MS). The detection of possible oviposition cues from oviposition substrates requires sensitive analytical methods. Volatiles detection was improved seven times. The detection of bacteria deoxyribonucleic acid (DNA) bands with DGGE was also improved to a minimum DNA concentration of 50 ng/µl. Results showed that ponds were colonized differently. Fresh ponds were preferred over slightly older ponds. Bacterial analysis revealed a low number of bacteria colony forming units (CFU) in preferred ponds. Some volatiles, including: 6,10-dimethyl-5,9-undecadien-2-one (geranylacetone) and 4-ethylbenzaldehyde, were associated with the oviposition preferred pond. In addition, low pH and high turbidity were associated with the ponds selected for oviposition. Finally, fungi isolated from the rhizomes of nut grass yielded a promising array of volatiles of which one is known to attract oviposition site seeking malaria mosquitoes. This finding opens the door for a cost effective and environmental friendly method of using fungi in an “attract and kill” strategy targeting malaria vectors. / Myggor i Anopheles gambiae sensu lato komplexet tillhör de myggor som är bäst på att sprida malaria parasiter i afrika söder om Sahara. Kunskapen om de här myggornas äggläggningsbeteende är begränsad. Den här kunskapen behövs för att kunna utveckla nya och förbättra tillgängliga malaria vektor kontroll metoder. Nya metoder som kan komplettera de som används idag (insecticides treated nets (ITNs) och indoor residual spraying (IRS)) behövs eftersom de metoderna har problem med resistensutveckling. Två studier utfördes på icipe fältstation i Mbita västra Kenya under 2012 och 2013 med målet att identifiera faktorer som påverkar myggornas äggläggningsbeteende. Baljor fyllda med en blandning av jord och vatten (äggläggningssubstrat) användes för att tillverka artificiella äggläggningsplatser som liknar de vattenpölar som de här myggarterna gärna lägger ägg i. Baljorna koloniserades av vilda myggor och antalet mygglarver som detekterades i baljorna jämfördes och användes som en proxy för äggläggningspreferens. Fysikaliska och kemiska parametrar mättes på jordvattenblandningarna i baljorna och prover togs för att analysera bakteriepopulationer med hjälp av denaturing gradient gel electrophoresis (DGGE) och flyktiga ämnen med hjälp av gas-kromatografi kopplat till mass-spektrometri (GC-MS). För att kunna detektera de låga halter av flyktiga ämnen och bakterier som fanns i de här proverna krävdes det känsliga metoder. Antalet flyktiga ämnen som kunde detekteras ökades sju gånger genom att tillsätta NaCl till vattenproverna innan doften insamlades och termisk desorption användes istället för lösningsmedels desorption. För att förbättra detektionsgränsen för bakterier amplifierades bakterie-DNA i två PCR reaktioner som sedan mixades och koncentrerades. Resultaten från fältstudierna med baljorna visade att de koloniserades olika av Anopheles myggorna. Baljor med nyblandat substrat innehöll dubbelt så många mygglarver som baljor med jord-vattensubstrat som åldrats under en längre tid. Lägre mängd bakterier, lägre pH och högre grumlighet var gemensamt för de baljor som myggorna föredrog. De flyktiga ämnen som detekterades i de olika baljor varierade mellan olika försök och inget ämne fanns med i alla upprepningar av ett försök. Trots det detekterades några ämnen oftare i de baljor som myggorna föredrog att lägga ägg jämfört med de med en mindre mängd mygglarver. De inkluderar geranylacetone och 4-ethylbenzaldehyde. Svampar isolerades från rotstockar av gräs som fanns i den jord som användes för att göra äggläggningssubstraten i fältstudierna. De flyktiga ämnen som avgavs från svampkulturerna analyserades. Bland annat så identifierades ett ämne som fungerar som en äggläggningsattrahent för An. gambiae s.l. myggor.Resultaten från den här avhandlingen kommer att kunna användas för att utveckla miljövänliga ”attract and kill” metoder för att kontrollera malaria myggor. / <p>QC 20160211</p>

Foi desenvolvido um estudo com o objetivo de avaliar o efeito de diferentes sistemas de pastejo e manejo da pastagem sobre o Intervalo Hídrico Ótimo (IHO). A amostragem foi realizada na área experimental do Centro Nacional de Pesquisa de Gado de Corte, unidade da Empresa Brasileira de Pesquisa Agropecuária (Embrapa Gado de Corte). O solo estudado foi um Latossolo Vermelho Distrófico argiloso. Foram avaliados quatro piquetes, sendo dois no sistema de pastejo contínuo e dois no sistema de pastejo rotacionado, e uma área de cerrado (CN). No sistema de pastejo contínuo, implementado com a espécie Brachiaria decumbens cv. Basilisk, foram retiradas 30 amostras por piquete, obedecendo a uma malha regular de 10 x 10 m, sendo que um dos piquetes não havia recebido adubação de manutenção (Cs) enquanto o outro havia recebido adubação bianual de manutenção (Cc). No sistema de pastejo rotacionado, implementado com a espécie Panicum maximum cv. Tanzânia, foram retiradas 60 amostras por piquete, sendo 30 na posição espacial touceira (t) e 30 na posição espacial entre touceiras (e), obedecendo a uma malha regular de 5 x 10 m. O diferencial entre os piquetes no sistema de pastejo rotacionado foi o resíduo pós pastejo. Em um dos piquetes o resíduo era de 2,0-2,5 Mg matéria seca total (MST) ha -1 (R1), enquanto no outro era de 3,0-3,5 Mg MST ha -1 (R2). No CN foram retiradas 30 amostras obedecendo a uma malha regular de 10 x 10 m. As amostras foram submetidas a um gradiente de tensão de água sendo posteriormente utilizadas nas determinações da densidade do solo (Ds), resistência à penetração de raízes (RP) e umidade volumétrica (qV). Em seguida, os resultados foram utilizados para o ajuste por regressão das curvas de resistência à penetração (CRP) e retenção de água do solo (CRA). Através da CRP e da CRA foi possível quantificar o IHO e a densidade crítica (Dsc), definida como o valor de Ds onde o IHO é igual a zero. O CN apresentou a melhor condição física do solo para o crescimento de plantas, sendo o IHO igual à água disponível. No sistema de pastejo contínuo estudado, a realização de adubação de manutenção não influenciou o IHO, o que foi atribuído às taxas de lotação animal equivalentes nos dois piquetes. O sistema de pastejo rotacionado apresentou as piores condições físicas do solo para o crescimento vegetal, avaliadas pelo critério do IHO. Os maiores valores de Ds e menor IHO foram observados no R1e, o que foi atribuído às taxas de lotação elevadas aplicadas neste piquete. A posição espacial de amostragem (touceira e entre touceiras) não exerceu influência sobre o IHO no R2 enquanto no R1 o IHO foi muito menor entre as touceiras, o que pode ser atribuído ao hábito de crescimento cespitoso da espécie Panicum maximum cv. Tanzânia, deixando parte do solo descoberto e, portanto, sujeito à ação direta do pisoteio dos animais. / A study was developed for evaluating the effect of different grazing systems and pasture management strategies on the Least Limiting Water Range (LLWR). The experimental site was located at the National Beef Cattle Research Center of Brazilian Agricultural Research Corporation (Embrapa Beef Cattle). The soil studied was a clay Oxisol (Typic Acrudox). Five sampling sites were selected: two under continuous grazing system, two under intensive short-duration grazing system, and one under native vegetation "cerrado" (CN). Thirty soil cores were collected in each site under continuous grazing system, established with Brachiaria decumbens cv. Basilisk species. Sampling at continuous grazing sites was performed in a 10 x 10 m regular grid. One of the continuos grazing sites had received biannual fertilization (Cc) while the other was not fertilized (Cs). Sixty soil cores were collected in each site under intensive short-duration grazing system, established with Panicum maximum cv. Tanzânia species, with thirty cores in the spatial position under the plants (up) and thirty cores in the spatial position between the plants (bp). Sampling at intensive short-duration grazing sites was performed in a 5 x 10 m regular grid. The difference between sites in intensive short-duration grazing system was the post-graze stubble. The post-graze stubble was 2,0-2,5 Mg total dry matter (TDM) ha -1 in one site (R1), and 3,0-3,5 Mg TDM ha -1 in the other (R2). Thirty soil cores were collected in CN, in a 10 x 10 m regular grid. The cores were subjected to a soil water suction gradient, and then used for soil bulk density (Db), soil penetration resistance (PR) and volumetric water content (qV) determinations. The data was used for developing soil resistance to penetration curve (SRP) and soil water retention curve (SWR) models doing regression fitting procedures. From SRP and SWR was possible to quantify the LLWR and the critical bulk density value (Dbc) identified as the Db value where LLWR is null. The CN site had the best soil physical condition for plant growth with the LLWR equal to available water. The fertilization did not influenced the LLWR in the continuos grazing system under evaluation, as a consequence of the similar stocking rates at both sites. The intensive short-duration grazing system had the worst soil physical condition for plant growth, as evaluated by the LLWR. The highest Db values and the lowest LLWR were found in R1bp, which may be a consequence of the high stocking rates observed at this site. The spatial sampling position (under the plants and between the plants) did not influenced the LLWR in the R2 site while in R1 the LLWR was much lower between plants. This result is a consequence of the cespitose growth habit of the Panicum maximum cv. Tanzânia species, which leaves part of the soil surface uncovered and subjected to a direct action of animal trampling.

Num ecossistema de pastagem a interceptação da luz incidente é o passo inicial de uma seqüência de eventos que resulta na produção de forragem. Vários são os fatores que interferem no processo de interceptação da luz e, dentre eles, os mais expressivos são aqueles relacionados com o índice de área foliar, com as características estruturais e com o arranjo espacial de componentes do dossel forrageiro. O presente experimento teve como objetivo estudar a estrutura do dossel, a interceptação luminosa e o acúmulo de forragem em pastos de Brachiaria brizantha cv. Marandu submetidos a lotação contínua por bovinos de corte. O experimento foi conduzido no Departamento de Zootecnia da USP/ESALQ. Os tratamentos corresponderam a quatro alturas de dossel (10, 20, 30 e 40 cm) mantidas constantes por meio de lotação contínua e taxa de lotação variável. O delineamento experimental foi o de blocos completos casualizados com quatro repetições. As variáveis estudadas foram: índice de área foliar (IAF), ângulo foliar, interceptação de luz, composição botânica/morfológica da forragem, distribuição vertical dos componentes do dossel forrageiro e acúmulo de forragem. A composição da massa de forragem dos pastos não apresentou grande variação entre tratamentos, principalmente no que diz respeito à porcentagem de hastes (27%) e de folhas (21%). A quantidade absoluta e a porcentagem de material morto em relação aos outros componentes morfológicos do dossel aumentaram do verão (30%) até o início da primavera (61%). Quanto maior a altura do dossel, maior foi o deslocamento dos componentes morfológicos ao longo de seu perfil vertical durante o ano. Reduções acentuadas nos valores de IAF dos pastos mantidos a 20 (5,2 para 1,6), 30 (7,0 para 1,5) e 40 cm (7,5 para 2,1) do verão ao início da primavera, respectivamente, não foram acompanhadas por reduções em interceptação luminosa, que se manteve consistentemente acima de 98%. O componente material morto interferiu de foma significativa na interceptação de luz, além de ter apresentado um padrão "dinâmico" de posicionamento no perfil vertical do dossel ao longo do ano. Essa variação na estrutura vertical do dossel foi tão maior quanto mais altos foram mantidos os pastos, e seu efeito sobre os padrões de interceptação luminosa provocou grandes variações na produção de forragem ao longo do ano. De toda a forragem produzida, 65 e praticamente 100% foi acumulada durante o final da primavera e verão nos pastos mantidos a 10 e 40 cm, respectivamente. A produção total de forragem não diferiu entre os pastos mantidos a 10, 20 e 30 cm (aproximadamente 24 ton.ha-1.ano-1), sugerindo haver grande flexibilidade de manejo para essa espécie forrageira. As modificações no sentido vertical e horizontal na estrutura do dossel forrageiro tiveram impacto maior sobre a distribuição estacional do que propriamente sobre a produção total de forragem. / In a pastoral ecossystem the interception of incident radiation is the first step of a sequence of events that results in herbage production. Several are the factors interfering on the light interception process including sward leaf area index, structure and architecture. The objective of this experiment was to study sward struture, light interception and herbage acummulation of Brachiaria brizantha cv. Marandu pastures submitted to continuous stocking by beef cattle. The experiment was carried out at Departamento de Zootecnia, USP/ESALQ. Treatments correspondended to four sward heights (10, 20, 30 and 40 cm) kept constant through continuous stocking and variable stocking rate, allocated to experimental units according to a complete randomized block design with four replications. The response variables evaluated were sward leaf area index (LAI), foliage angle, light interception, botanical and morphological composition and hebarge production. There was no significant change in hebarge mass composition with stems representing 27% and leaves 21% of the sward. Quantity and proportion of dead material relative to the other sward morphological components increased from Summer (30%) to early Spring (61%). The taller the swards, the larger was the shift in the position of the morphological components across the vertical sward profile throughout the year. Significant reductions in LAI values for the 20 cm (5,2 to 1,6), 30 cm (7,0 to 1,5) and 40 cm swards (7,5 to 2,1) from Summer to early Spring were not followed by reduction in light interception, which remained above 98% consistent by through out the year around. The dead material component played an important role on sward light interception, and its placement across the vertical sward profile exhibited a "dynamic" pattern of variation. This variation was more evident in taller swards and affected sward light interception, resulting in varying seasonalities of herbage production. From the total herbage yield, 65 and 100% was produced during late Spring and Summer on the 10 and 40 cm swards, respectively. There was no difference in total herbage production among swards maintained at 10, 20 and 30 cm (24 ton.ha-1.year-1), sugesting that there is a large flexibilitty in grazing management for Brachiaria brizantha cv. Marandu. Modifications in both vertical and horizontal structure of the sward were more effective in changing the seasonal pattern of herbage production than determining herbage yield.