Leaf blade nutritional quality of two regrowths of Festuca arundinacea differing in stubble height (40 mm and 100 mm) was evaluated during spring-summer (2011-2012). The experiment was conducted outdoor without limitations of water, N and P, in 500-pots arranged in a completely randomised design (n=3). The leaf elongation rate (LER), leaf appearance interval (LAI), leaf life span (LLS), number of living leaves (NLL) and length of the leaf blade and sheath were measured in 15 marked tillers per treatment. In parallel, three destructive harvests of 6 pots/treatment/replicate were performed when two, three and four leaves were accumulated per tiller (2L, 3L and 4L, respectively). The NDF, NDF digestibility (NDFD) and the DM apparent digestibility (DMD) were determined in leaf blades, by in vitro 24 h-incubation (DaisyII digestor). Parameters of morphogenesis were evaluated using repeated measures analysis and those of quality were analysed by regression functions with leaf age and length and dummy variables. The mean values of treatments in each leaf stage were compared by ANOVA (Tukey). The mean daily temperature of regrowth was 19.7±3 °C. Stubble height affected leaf morphogenesis, structure and quality. The lower stubble height regrowth showed a shorter sheath tube length (65 vs 130 mm), leaf blade length (444 vs 629 mm), LER (16 vs 25 mm.day-1) and LAI (275 vs 354°Cd), but similar LLS (629±34 GDD). It is also had higher NLL (2.5 vs 2.0) and leaf blades of higher quality. NDFD increased 16% and DMD 9%, but NDF did not differ between treatments (62.3±0.6%). It is concluded that changes occasioned by reduction of sheath tube length on leaf morphogenesis, sward structure and fiber digestibility favour the nutritional quality of regrowth.

Se evaluó la calidad nutritiva de las láminas de rebrotes de Festuca arundinacea provenientes de dos tratamientos de corte de distinta altura de remanentes (40 mm y 100 mm). El experimento se realizó en 500 macetas al aire libre sin limitantes hídricas ni de N y P, en un diseño completamente aleatorizado (n=3) en la primavera-verano 2011-2012. Se midió la tasa de Elongación Foliar (TEF), Intervalo de Aparición de Hoja (IAH), Vida Media Foliar (VMF), Número de Hojas Vivas (NHV) y largo de lámina y vaina en 15 macollos marcados por tratamiento. Paralelamente, se realizaron tres cosechas destructivas de 6 macetas/tratamiento/ repetición, cuando la pastura tenía 2, 3 y 4 hojas acumuladas por macollo (2H, 3H y 4H, respectivamente). En las láminas se determinó el contenido de Fibra Detergente Neutro (FDN), la digestibilidad de la FDN (DFDN) y la Digestibilidad Aparente de la Materia Seca (DAMS) a 24 h de incubación in vitro (digestor DaisyII, ANKOM). Las variables de morfogénesis se analizaron como medidas repetidas en el tiempo, y las de calidad ajustando funciones de regresión con la edad y largo foliar. Las comparaciones se realizaron mediante análisis de variables Dummy y ANVA (Tukey). La temperatura media diaria del rebrote fue de 19,7±3° C. La altura del remanente afectó la morfogénesis, estructura foliar y la calidad de las láminas del rebrote. El remanente más bajo produjo un rebrote con vainas más cortas (65 vs. 130 mm), láminas de menor longitud (444 vs. 629 mm), de menor TEF (16 vs. 25 mm.día-1) e IAH (275 vs. 354°Cd), sin diferenciarse en VMF (629±34 GDC). También tuvo más hojas vivas por macollo (2,5 vs. 2,0 hojas vivas.macollo-1) y láminas de mayor calidad. Estas tuvieron un aumento del 16% en la DFDN, de 9% en la DAMS y similar FDN (62,3±0,6%). Se concluye que los cambios ocasionados por la reducción del tubo de vainas en la morfogénesis, en la estructura foliar y en la digestibilidad de la fibra favorecen la calidad del rebrote.

The effect leaf morphoenesis and structure onleaf bades quality was evaluated in summer and autumn regrowths of Festuca arundinacea Schreb. The experiment was conducted in 250 pots arranged in a completely randomised design (n=3) under natural climate conditions, without limitation of water, N and P. In each season swards were sampled 3 times (~300 tillers/replicate) to obtain leaves in 3 ontogenics stages of similar age (just expanded, adult and pre-senescence) corresponding to the 3 first sequentially appearing leaf generations. The leaf elongation rate (LER), leaf app earance interval (LAI), leaf life span (LLS), numb er of living leaves (NLL) and length of the leaf blade and sheath were measured in 5 marked tillers/replicate. In leaf blades, the NDF and the in vitro digestibility (NDFD and DMD) were determined (incubation at 24 h DaisyII digestor). The mo rphog enic variables were evaluated using repeated measures data analysis. Quality traits were analyzed by lineal function with age and leaf length. Comp arisons were made by dummy variable regressions and ANOVA (Tukey). The mean daily temp erature was low er in autumn than in summ er (13±4 vs. 21±3ºC). LER, LLS and LAI were low er (p<0.001) in autumn than in summ er but NLL was similar (p>0.23) in bo th season. Leaf length did not vary during autumn regrow th, but it was shorter than summ er (106±9 vs 239±98 mm ). Leaf blade length increased during summ er amo ng successive leaves of regrow th (~110 mm /generation) in relation (R²=93%) to the prog ressive in crease of the sheath tube length. Autumn leaf blades show ed low er NDF (39,8±0,8 vs 55,3±0,6%), higher NDFD (52,7±1,6 vs 46,8±1,1%) and DMD (69,3±0,9 vs 58,7±0,6%%) than that of summ er regrow th. It is concluded that summ er and autumn regrow ths differ in mo rphog enic, structure and quality variables, and that differences in DM digestibility were associated with the effect of leaf length on NDF and NDFD dynamics.

Se evaluó el efecto de la morfogénesis y estructura foliar en la calidad de las láminas de rebrotes de verano y otoño de Festuca arundinacea Schreb. Se utilizó un diseño completamente aleatorizado (n=3) en 250 macetas al aire libre sin limitantes hídricas de N y P. En los rebrotes de cada estación se realizaron tres cosechas de 300 macollos/repetición para obtener láminas en tres estados de desarrollo (recientemente expandida, adulta y pre-senescencia), correspondientes a tres generaciones consecutivas de hojas. En cinco macollos marcados por repetición se midió: la tasa de elongación foliar (TEF), el intervalo de aparición de hoja (IAH), la vida media foliar (VMF), el número de hojas vivas (NHV) y el largo de lámina y vaina. En las láminas se determinó el contenido de fibra detergente neutro (FDN), la digestibilidad de la FDN (DFDN) y la digestibilidad in vitro aparente de la materia seca (DAMS) (24 h de incubación, digestor DaisyII, ANKOM). Las variables de morfogénesis se evaluaron como medidas repetidas en el tiempo, y las de calidad ajustando funciones lineales con la edad y largo foliar. Las comparaciones se realizaron mediante análisis de variables Dummy y ANVA (Tukey). La temperatura media diaria del rebrote de otoño fue menor que en verano (13±4 vs. 21±3ºC). Los parámetros de morfogénesis TEF, VMF, IAH fueron menores (p<0,001) en otoño que en verano, pero el NHV no fue afectado (p>0,23). La longitud foliar en otoño no varió durante el rebrote y fue menor que en verano (106±10 vs 239±100 mm); que aumentó entre generaciones sucesivas (~110 mm/generación) en estrecha asociación (R²=93%) con el aumento progresivo de la longitud de vaina. Las láminas de otoño presentaron menor contenido de FDN (39,8±0,8 vs. 55,3±0,6%), mayor DFDN (52,7±1,6 vs. 46,8±1,1%) y DAMS (69,3±0,9 vs. 58,7±0,6%%) que las de verano. Se concluye que los rebrotes de verano y otoño difirieron en variables de morfogénesis, estructura y calidad. Asimismo, las diferencias en digestibilidad de la MS estuvieron asociadas al efecto del largo foliar en la dinámica de la FDN y DFDN.

The effect of leaf age and length on leaf blade quality was studied in wheatgrass leaf blades leaves (Thinopyrum ponticum cv. Hulk) from swards of two heights. Swards were grown in plots in a greenhouse (17± 4 ºC) in a randomized block design (n=3) of 160 plots/block. Leaves in 6 ontogenic stages from 3 consecutive leaf generations (from early growth to advanced senescence) were obtained from vegetative tillers (~200/harvest) harvested along 52 days of regrowth, with a frequency 80 GDD (growing degree days: Σ t1/2- 4,5 ºC). The leaf lifespan (LLS), leaf appearance interval (LAI), leaf and sheath lengths, NDF content and NDF digestibility (NDFD) were measured. The relationships among quality and morphogenic parameters were studied by linear regression and data analyzed as a complete randomized block design with factorial arrangement (2 heights x 3 leaf generations) and means compared by Tukey test (5%). The shorter leaf sward (241.8 vs 458.4 mm) had longer LLS (453.6 vs 337.8 GGD), similar NDF content and higher NDFD (~10%). In both swards the NDFD decreased linearly with leaf age and length, but NDF remained unchanged during the LLS. It is concluded that the NDFD declines with leaf age and length during regrowth, however shorter sward height delays senescence (>LLS), increases tiller leaving leaf number and improves leaf blade quality.

Se estudió el efecto de la edad y largo foliar en la calidad de láminas de agropiro alargado (Thinopyrum ponticum cv. Hulk) en un rebrote otoñal de dos alturas. El ensayo se realizó en invernáculo (17± 4 ºC) en un diseño BCA (n=3) de 160 macetas por bloque. Se estudiaron láminas de 3 generaciones sucesivas de hojas en 6 estados ontogénicos (de crecimiento hasta senescencia avanzada). Las láminas se obtuvieron de ~200 macollos vegetativos/cosecha, muestreados a lo largo de 52 días de rebrote, con una frecuencia de 80 GDC (grados día de crecimiento: Σ t1/2- 4,5 ºC). Se midió la vida media foliar (VMF), el intervalo de aparición (IAH), largo de lámina y vaina, contenido de FDN y digestibilidad in vitro de la FDN (DFDN). Se realizaron ajustes lineales entre variables de calidad con edad y largo de hoja y se compararon pendientes y ordenadas al origen (PROC REG de SAS). El resto de las variables se analizaron según BCA con arreglo factorial (2 alturas x 3 generaciones de hoja) utilizando el procedimiento GLM de SAS. Las medias se compararon por el test de Tukey al 5%. La pastura de menor altura (241,8 vs 458,4 mm) tuvo mayor VMF (453,6 vs 337,8 GDC), similar contenido de FDN (52,3%) y mayor DFDN (~10%). En ambas pasturas la DFDN disminuyó linealmente con la edad y el largo foliar, pero la FDN no fue afectada durante la VMF. Se concluye que durante el rebrote la DFDN disminuye con la edad y el aumento del largo foliar entre hojas sucesivas y que la reducción de la altura de la pastura retrasa la senescencia (>VMF), aumenta el número de hojas vivas por macollo y la calidad de las láminas.

Leaf nutritive qualitywas evaluated in two tall fescue (Festuca arundinaceaSchreb) cultivars, during a summer regrowth (average daily temperature: 21±2.8°C), in relation to morphogenesis parameters. Cultivars were El Palenque PlusINTA (traditional) and Grasslands AdvanceGentos (soft leaf type). The experiment was conducted in pots (250/cultivar) arranged in a completely randomised design (n=3) under natural climate conditions, with out limitation of water, N and P. Swards were sampled 8 times (~300 tillers/harvest) over a period of 14 weeks, to obtain leaves in 6 ontogenics stages of similar age (from growing to complete senescence) corresponding to the 3 first sequentially appearing leaf generations (G1, G2, G3). Morphogenesis traits were measured in 15 marked tillers/cultivar. Leaf age, leaf lifespan (LLS) and leaf appearance interval (LAI) were expressed in growing degree days (GDD:Σaverage temperature - 4.0 ºC). Leaf blades and sheaths were measured and leaf blade NDF and the in vitro digestibility (NDFD and DMD, incubation at 24 h DaisyII digestor) were determined. The morphogenesis traits were evaluated using repeated measures data analysis. Quality traits were analyzed by lineal function and dummy variables.The mean values of cultivars in each ontogenetic state were compared by ANOVA (Tukey, p <0.05). Cultivar did not differ in morphogenesis traits, with the exception of LLS and number of leaving leaves (NLL), which were lower in Advance. The NDFD declined with leaf age and length in both cultivars, with higher rate in Advance due to its shorter LLS. However, cultivars did not differ in NDF content, which remained stable throughout the leaf lifespan (54.5±3%) and increased during senescence (64.9±0.8%). Cultivars did not differ in NDFD at similar ontogenic stages, which indicates that Advance require more frequent defoliations than El Palenque to control changes of quality over time.

Se evaluó la calidad nutritiva de dos cultivares de festuca alta (Festuca arundinacea Schreb) durante un rebrote estival (temperatura media: 21±2.8 °C), en relación a la morfogénesis de dos cultivares (Tradicional: El Palenque PlusINTA y Hojas flexibles: Grasslands AdvanceGentos). El diseño fue completamente aleatorizado (n=3) en 250 macetas/cultivar al aire libre, sin limitantes hídricas ni de N y P. Se realizaron 8 cosechas destructivas de 300 macollos vegetativos/cosecha en un período 14 semanas. La frecuencia se ajustó al estado ontogénico de las hojas para obtener láminas en 6 estados de similar edad térmica (desde el inicio de crecimiento a la senescencia completa) de 3 generaciones consecutivas de hojas (G1, G2 y G3). Las variables de morfogénesis se midieron en 15 macollos marcados por cultivar. La edad, Vida Media Foliar (VMF) e Intervalo de Aparición de Hoja (IAH) se expresaron en Grados Días de Crecimiento (GDC: ΣTem½ - 4 ºC). En las hojas se midió la longitud de las láminas y vainas; y en las láminas el contenido de Fibra Detergente Neutro (FDN) y la digestibilidad in vitro de la FDN (DFDN) y de la MS (DAMS) por incubación a 24 horas en digestor DaisyII. Las variables de morfogénesis se evaluaron como medidas repetidas en el tiempo; y para las de calidad se ajustaron funciones lineales con la edad y el largo foliar, y se compararon mediante análisis de variables dummy. Los cultivares no se diferenciaron en morfogénesis, con excepción de la VMF y el Número de Hojas Vivas por macollo (NHV) que fueron menores para Advance. La DFDN de ambos cultivares disminuyó linealmente con la edad y con el aumento del largo foliar entre hojas sucesivas de rebrote, con mayor tasa en Advance. Pero el contenido de FDN no se diferenció entre cultivares, sino que se mantuvo constante durante la vida foliar (54,5±3,2%) y aumentó durante la senescencia (64,9±0,8%). Los cultivares no se diferenciaron en calidad al mismo estado ontogénico, lo cual indica que Advance, por tener menor VMF, requiere defoliaciones más frecuentes que El Palenque Plus para controlar los cambios de calidad en el tiempo.

A degradabilidade in situ da matéria seca (MS) de silagens de milho em dois estados de maturidade (grão leitoso e meia linha de leite), de conhecida digestibilidade in vivo e in vitro, foi determinada com o propósito principal de comparar valores de digestibilidade com a degradabilidade no rúmen após 24 e 48h de incubação. Também foi analisada a cinética da digestão no rúmen, pelo modelo exponencial de McDonald, e foi calculada a degradabilidade efetiva, assumindo uma taxa de passagem de 4%/h. Dados de digestibilidade in vivo, in vitro e de degradabilidade in situ a 24 e 48h foram analisados com um modelo linear que incluiu o efeito do estado de maturação e metodologia de avaliação. Houve efeito significativo (P<0,05) da metodologia na estimação da digestibilidade, mas não foi encontrado efeito da maturação ou da interação maturação × metodologia. A digestibilidade in vivo (52,9%) não foi diferente da degradabilidade in situ a 24h (55,6%), e apresentou valores numéricos na amplitude dos valores da degradabilidade efetiva. A digestibilidade in vitro (61,6%) não foi diferente da degradabilidade in situ a 48h (61,9%), e ambas as alternativas foram maiores do que a digestilidade in vivo. A degradabilidade in situ a 24h de incubação é um bom preditor da digestibilidade in vivo da silagem de milho. Este parâmetro foi superestimado em 15-20% pela digestibilidade in vitro e pela degradabilidade in situ a 48h de incubação.

The in situ dry matter (DM) disappearance of corn silages in two maturity stages (milk grain and half milk line) of known in vivo and in vitro digestibility was determined, with the main purpose of comparing digestibility values with the ruminal disappearance at 24 and 48h of incubation. A secondary goal was the description of their ruminal digestion kinetics, from which the effective degradability was calculated at an assumed passage rate of 4%/h. Data of in vivo, in vitro and in situ degradability at 24 and 48-h were analyzed with a linear model that included as fixed effects the maturity and the methodology of evaluation, and the kinetic data were described by the exponential model of McDonald. There was a significant effect (P<0.05) of methodology in the estimation of digestibility, but not of maturity or interaction maturity × methodology. The in vivo digestibility (52.9%) was not different from the 24-h in situ degradability (55.6%) with numerical values in the range of the effective degradability. The in vitro digestibility (61.6%) was not different from the 48-h in situ degradability (61.9%), being both estimates higher than the in vivo digestibility. The 24-h in situ degradability was a closer estimator of the in vivo digestibility and the 48-h in situ degradability and the in vitro digestibility overestimated the in vivo parameter by 15-20%.

Estimou-se para animais em pastejo o incremento relativo no custo diário de manutenção devido a atividade. As atividades consideradas foram a apreensão de forragem e o caminhar. Utilizaram-se índices de gasto de energia para cada atividade, obtidos em experimentos realizados com novilhos Aberdeen Angus entre os anos 1993 e 1995 em Balcarce (Argentina), empregando a técnica da taxa de entrada ou incorporação do 14C para estimar o gasto energético. Além disso, utilizaram-se dados da bibliografia da duração do pastejo e da distância percorrida, e da velocidade ao caminhar, em situação normal de produção. As estimativas mostraram que no gado em pastejo o custo de manutenção pode ser 8 a 30% maior em relação ao custo de manutenção dos animais em curral. Essa variação depende fundamentalmente das características da pastagem. Conclui-se que a ingestão de forragem em alta taxa de apreensão é a variável de maior influência no custo diário de manutenção dos animais em pastejo, enquanto que a ingestão de forragem em taxa moderada de apreensão e o caminhar têm efeito menor no custo.

The relative increment in daily maintenance requirement by physical activity was estimated in free-grazing cattle. The effects of forage harvesting and walking were measured and expressed as an index in relation to the value of energy expenditure of animals in corrals. All indices were obtained from experiments conducted in Balcarce (Argentina) from 1993 to 1995. Energy expenditure of Aberdeen Angus steers was estimated by the 14C-entry rate technique, on animals standing still in a corral, grazing at two different biting rates or walking at four different speeds. Information on time spent on grazing and distance traveled was obtained from the literature. These estimations indicate that the maintenance cost of cattle in corrals could be increased on pastures by a factor of 1.08 to 1.30, depending upon the grazing conditions. It was observed that grazing at high biting rate was the variable of highest effect on maintenance energy cost, and that walking or grazing at moderate biting rate was of lower incidence.