Wet distiller’s grains with solubles are the most common feedstuff generated by the ethanol industry, and this feedstuff has been utilized by the feedlot industry. Exploration of the effect of dietary distiller’s inclusion on the form and quantity of protein or nitrogen (N) has received little attention. Assessment of degradable N needs in diets containing wet distiller’s grains with solubles (WDGS) is needed to aid the cattle feeding industry in managing feed costs and potential environmental issues. In Exp. 1, 525 yearling steers (initial weight = 373 ±13 kg) received treatments in a 2 × 3 1 factorial. Factors included corn WDGS (15 or 30 percent of DM) and non-protein N (NPN; 0, 1.5, or 3.0 percent of DM) from urea. The control diet without corn WDGS contained 3.0 percent NPN (1.06 percent urea) and cottonseed meal. Overall gain efficiency among steers fed 15 percent corn WDGS was greatest for 1.5 percent NPN and least for 0 percent NPN (P = 0.07, quadratic), whereas gain efficiency decreased linearly (P < 0.09) as NPN increased in the 30 percent WDGS. Dressing percent was greater (P < 0.01) for the control diet than for 15 percent or 30 percent WDGS. In Exp. 2, 296 steer calves (initial BW = 344 ± 12 kg) were adapted to a common finishing diet, blocked by BW, and assigned to treatments. Experimental diets included a control diet without WDGS (contained 3 percent NPN from urea, and cottonseed meal) and 15 percent WDGS with either 1.50, 2.25, or 3.00 percent NPN (0.52, 0.78, and 1.04 percent urea, respectively, on a DM basis). Overall gain efficiency on either a live or adjusted basis was not different among treatments (P > 0.15). Dietary NPN concentration did not influence growth performance (P > 0.21). Results suggest that optimum performance for cattle fed 15 percent WDGS occurred when the diet contained between 1.5 percent and 2.25 percent NPN. However, removing all supplemental NPN was necessary to support optimum performance in diets containing 30 percent WCDG.

Bacteroids of B. japonicum from nodules of soybean roots were isolated using differential centrifugation (the standard bench method) and density gradient centrifugation methods (either sucrose- or Percoll-) under anaerobic conditions in which N2 fixation was preserved. The relationships between N2 fixation and respiration, O2 supply, O2 demand, substrate (mainly malate) transport and metabolism in bacteroids were investigated using the flow chamber system. In related experiments, the primary products of N2 fixation which leave the bacteroids were investigated using a 15N-labelling technique in a closed shaken system and other biochemical methods.¶ In the flow chamber experiments, the rates at which O2 was supplied to bacteroids in the chamber were varied by (a) changing the flow rate of reaction medium through the chamber; (b) by changing the [O2 free] in the inflowing reaction medium by using either 3-5% (v/v) or 100% air in the gas mixture above the stirred reaction medium in two reservoir flasks; (c) by successively withdrawing bacteroids from the chamber, thus increasing the supply of O2 per bacteroid to those remaining in the chamber. The results showed that the rate of O2 supply regulates respiratory demand for O2 by bacteroids rather than the O2 concentration present in the reaction system. Respiration is always coupled to N2 fixation. ¶ Uptake of malate by bacteroids withdrawn from the flow chamber was measured under microaerobic conditions. Malate uptake by these N2-fixing bacteroids was lower than that by bacteroids isolated under aerobic conditions, which eliminate N2 fixation of bacteroids, but is closely correlated with bacteroid respiration rates. When respiration was increased by an increase in O2 supply, malate uptake by bacteroids was also increased. This suggested that transport of malate through the bacteroid membrane is also regulated by O2 supply, but indirectly. Higher uptake by bacteroids under aerobic conditions was observed because respiration was enhanced by the high availability of O2, but the fast uptake of malate by bacteroids driven by the abnormal respiration rates may not reflect the reality of malate demand in vivo by bacteroids when N2 fixation by bacteroids is fully coupled. ¶ The results of 15N labelling experiments and other biochemical assays once again demonstrated that ammonia is the principal significant 15N labelled product of N2 fixation accumulated during 30 min in shaken assays with 0.008-0.01 atm O2. Alanine although sometimes found in low concentrations in the flow chamber reactions, was not labelled with 15N in shaken closed system experiments. No evidence could be obtained from the other biochemical assays, either. Therefore, it is concluded that these and earlier results were not due to contamination with host cytosolic enzymes as suggested by Waters et al. (Proc. Natl. Aca. Sci. 95, 1998, pp 12038-12042). ¶ Malate transported into bacteroids is oxidized in a modified TCA cycle present in bacteroids. The results of flow chamber experiments with a sucA mutant (lacking a-ketoglutarate dehydrogenase) showed that respiratory demand for O2 by the mutant bacteroids is regulated by O2 supply in the same way as the wild-type. Despite differences in other symbiotic properties, rates of nitrogen fixation by the mutant bacteroids, based on the bacteroid dry weight, appeared to be the same as in the wild-type. Also N2 fixation was closely coupled with respiration in the same manner in both mutant bacteroids and wild type bacteroids. These results and other supporting data, strongly support the conclusion that there is an alternative pathway of the TCA cycle in bacteroids, which enables the missing step in the mutant to be by-passed with sufficient activity to support metabolism of transported malate.

Recentemente o conceito de alvo de manejo tem sido utilizado para definição de estratégias de manejo do pastejo, com a altura do pasto, dentre outras características estruturais do dossel, assumindo um papel importante para implementação desse conceito em condições de campo. Práticas de manejo podem influenciar de forma diferente os processos de crescimento e senescência, afetando assim a estrutura e o acúmulo de forragem e, por essa razão, precisam ter seu efeito conhecido de forma a permitir o planejamento práticas de manejo do pastejo eficientes e sustentáveis. Dentro desse contexto, o objetivo deste experimento foi avaliar a estrutura do dossel forrageiro, seus padrões de variação ao longo do ano e a dinâmica do acúmulo de forragem em pastos de capim-marandu mantidos a 30 cm de altura por meio de lotação contínua e submetidos a ritmos de crescimento contrastantes de janeiro de 2007 a abril de 2008. Os tratamentos corresponderam à aplicação de três doses de nitrogênio (150, 300 e 450 kg/ha de N) mais o controle (sem adubação), e foram alocados às unidades experimentais (piquetes de 1200 m2) segundo um delineamento de blocos completos casualizados, com quatro repetições. Foram avaliadas as seguintes variáveis-resposta: massa de forragem, composição morfológica, índice de área foliar, ângulo da folhagem, interceptação luminosa do dossel, densidade populacional de perfilhos e as taxas de crescimento total, de folhas, de colmos, da senescência e do acúmulo líquido de forragem. De forma geral, a aceleração dos ritmos de crescimento dos pastos resultou em aumento da massa de forragem, porcentagem de folhas e de colmos e redução da porcentagem de material morto, modificações essas coerentes com o maior IAF, maior densidade populacional de perfilho e menor ângulo da folhagem, porém sem alteração em interceptação de luz. Essas variações estruturais, apesar de pequenas, resultaram em aumento das taxas de crescimento de folhas, total, e de acúmulo líquido de forragem nos pastos adubados com as maiores doses de N. Apesar da grande amplitude entre as doses de N utilizadas, foi possível detectar um padrão comum de variação na estrutura do dossel forrageiro, cuja diferença entre tratamentos foi apenas relacionada à ordem de grandeza da variação registrada, conseqüência do maior ou menor ritmo de crescimento dos pastos. As mudanças em estrutura do dossel e acúmulo de forragem foram maiores em função da época do ano relativamente às doses de N utilizadas. Ritmos mais acelerados de crescimento associados com as doses mais altas de N resultaram em aumento de crescimento e de senescência, os quais ocorreram de forma relativamente proporcional, sugerindo um forte mecanismo compensatório que impede que grandes mudanças em eficiência de utilização da forragem produzida sejam obtidas. Os resultados demonstraram consistência e robustez da altura como critério de campo, e aponta para a possibilidade de seu uso como forma eficiente de monitorar e controlar o processo de pastejo e a estrutura do dossel forrageiro. Por outro lado, revelaram a necessidade de planejamento cuidadoso e uso estratégico do nitrogênio como forma de assegurar elevada produção de forragem, eficiência de utilização, desempenho e produtividade animal. / Recently, the concept of sward target has been used to define grazing management strategies, with sward surface height, among other swards structural characteristics, assuming an important role for implementing it in field conditions. Management practices can influence growth and senescence processes differently, interfering with herbage accumulation and, therefore, need to have their effect known in order to allow adequate planning of efficient and sustainable grazing management practices. Against that background, the objective of this study was to evaluate sward structure and its patterns of change throughout the year and the dynamics of herbage accumulation on continuously stocked marandu palisadegrass swards maintained at 30 cm and subjected to contrasting rhythms of growth from January 2007 to April 2008. Treatments corresponded to three nitrogen application rates (150, 300 and 450 kg ha-1 N) plus the control (no N fertilisation), and were allocated to experimental units (1200 m2 paddocks) according to a complete randomised block design, with four replications. The following response variables were evaluated: sward herbage mass, morphological composition, leaf area index (LAI), foliage angle, canopy light interception, tiller population density and the rates of total, leaf and stem growth, senescence, net herbage accumulation. Overall, the increase in nitrogen application rates resulted in increase of sward herbage mass, leaf and stem percentage and decrease of dead material percentage, modifications in line with the increase in LAI, light interception and tiller population density and decrease in foliage angle. These changes in sward structural characteristics were relatively small, but resulted in increased rates of total and leaf growth as well as net herbage accumulation on swards fertilised with high rates of nitrogen application. In spite of the wide range of nitrogen application rates used, it was possible to detect a common pattern of variation in sward structure, there was a common pattern of variation in sward structure, and treatments differences were related only to the size of the variation recorded, consequence of the faster or slower growth rhythm of swards. Changes in sward structure and herbage accumulation were larger with season of the year relative to nitrogen application rates. Faster growth rhythms associated with high nitrogen application rates resulted in proportionately similar increases in growth and senescence, suggesting a strong compensatory mechanism that would avoid that significant variations in utilisation efficiency were obtained. This indicates consistency and robustness of sward height as a field indicator, and highlights the possibility of using it as an efficient management tool to monitor and control the grazing process and sward structure. Further, it also highlights the need for careful planning and strategic use of nitrogen as a means of ensuring high levels of herbage production, utilisation efficiency, animal performance and productivity.

Recentemente o conceito de alvo de manejo tem sido utilizado para definição de estratégias de manejo do pastejo, com a altura do pasto, dentre outras características estruturais do dossel, assumindo um papel importante para implementação desse conceito em condições de campo. Práticas de manejo podem influenciar de forma diferente os processos de crescimento e senescência, afetando assim a estrutura e o acúmulo de forragem e, por essa razão, precisam ter seu efeito conhecido de forma a permitir o planejamento práticas de manejo do pastejo eficientes e sustentáveis. Dentro desse contexto, o objetivo deste experimento foi avaliar a estrutura do dossel forrageiro, seus padrões de variação ao longo do ano e a dinâmica do acúmulo de forragem em pastos de capim-marandu mantidos a 30 cm de altura por meio de lotação contínua e submetidos a ritmos de crescimento contrastantes de janeiro de 2007 a abril de 2008. Os tratamentos corresponderam à aplicação de três doses de nitrogênio (150, 300 e 450 kg/ha de N) mais o controle (sem adubação), e foram alocados às unidades experimentais (piquetes de 1200 m2) segundo um delineamento de blocos completos casualizados, com quatro repetições. Foram avaliadas as seguintes variáveis-resposta: massa de forragem, composição morfológica, índice de área foliar, ângulo da folhagem, interceptação luminosa do dossel, densidade populacional de perfilhos e as taxas de crescimento total, de folhas, de colmos, da senescência e do acúmulo líquido de forragem. De forma geral, a aceleração dos ritmos de crescimento dos pastos resultou em aumento da massa de forragem, porcentagem de folhas e de colmos e redução da porcentagem de material morto, modificações essas coerentes com o maior IAF, maior densidade populacional de perfilho e menor ângulo da folhagem, porém sem alteração em interceptação de luz. Essas variações estruturais, apesar de pequenas, resultaram em aumento das taxas de crescimento de folhas, total, e de acúmulo líquido de forragem nos pastos adubados com as maiores doses de N. Apesar da grande amplitude entre as doses de N utilizadas, foi possível detectar um padrão comum de variação na estrutura do dossel forrageiro, cuja diferença entre tratamentos foi apenas relacionada à ordem de grandeza da variação registrada, conseqüência do maior ou menor ritmo de crescimento dos pastos. As mudanças em estrutura do dossel e acúmulo de forragem foram maiores em função da época do ano relativamente às doses de N utilizadas. Ritmos mais acelerados de crescimento associados com as doses mais altas de N resultaram em aumento de crescimento e de senescência, os quais ocorreram de forma relativamente proporcional, sugerindo um forte mecanismo compensatório que impede que grandes mudanças em eficiência de utilização da forragem produzida sejam obtidas. Os resultados demonstraram consistência e robustez da altura como critério de campo, e aponta para a possibilidade de seu uso como forma eficiente de monitorar e controlar o processo de pastejo e a estrutura do dossel forrageiro. Por outro lado, revelaram a necessidade de planejamento cuidadoso e uso estratégico do nitrogênio como forma de assegurar elevada produção de forragem, eficiência de utilização, desempenho e produtividade animal. / Recently, the concept of sward target has been used to define grazing management strategies, with sward surface height, among other swards structural characteristics, assuming an important role for implementing it in field conditions. Management practices can influence growth and senescence processes differently, interfering with herbage accumulation and, therefore, need to have their effect known in order to allow adequate planning of efficient and sustainable grazing management practices. Against that background, the objective of this study was to evaluate sward structure and its patterns of change throughout the year and the dynamics of herbage accumulation on continuously stocked marandu palisadegrass swards maintained at 30 cm and subjected to contrasting rhythms of growth from January 2007 to April 2008. Treatments corresponded to three nitrogen application rates (150, 300 and 450 kg ha-1 N) plus the control (no N fertilisation), and were allocated to experimental units (1200 m2 paddocks) according to a complete randomised block design, with four replications. The following response variables were evaluated: sward herbage mass, morphological composition, leaf area index (LAI), foliage angle, canopy light interception, tiller population density and the rates of total, leaf and stem growth, senescence, net herbage accumulation. Overall, the increase in nitrogen application rates resulted in increase of sward herbage mass, leaf and stem percentage and decrease of dead material percentage, modifications in line with the increase in LAI, light interception and tiller population density and decrease in foliage angle. These changes in sward structural characteristics were relatively small, but resulted in increased rates of total and leaf growth as well as net herbage accumulation on swards fertilised with high rates of nitrogen application. In spite of the wide range of nitrogen application rates used, it was possible to detect a common pattern of variation in sward structure, there was a common pattern of variation in sward structure, and treatments differences were related only to the size of the variation recorded, consequence of the faster or slower growth rhythm of swards. Changes in sward structure and herbage accumulation were larger with season of the year relative to nitrogen application rates. Faster growth rhythms associated with high nitrogen application rates resulted in proportionately similar increases in growth and senescence, suggesting a strong compensatory mechanism that would avoid that significant variations in utilisation efficiency were obtained. This indicates consistency and robustness of sward height as a field indicator, and highlights the possibility of using it as an efficient management tool to monitor and control the grazing process and sward structure. Further, it also highlights the need for careful planning and strategic use of nitrogen as a means of ensuring high levels of herbage production, utilisation efficiency, animal performance and productivity.