ABSTRACT Objective : To evaluate the fermentative and organoleptic quality of silages with different proportions of forage and root of two varieties of Manihot esculenta Crantz in Matanzas province, Cuba. Materials and Methods : A study was conducted in the nutrition laboratory of the Pastures and Forages Research Station Indio Hatuey, where the fermentative quality of two M. esculenta varieties (INIVIT Y-93-4 and Señorita), as well as the organoleptic quality of the produced silage, was evaluated. A complete randomized design was applied with three treatments, where each variety was evaluated separately: T1) 0 % foliage: 100 % root; T2) 25 % foliage: 75 % root and T3) 100 % foliage: 0 % root, at four moments of evaluation. Variance analysis was carried out and to determine the difference among means Duncan’s test was used. The data were processed through the statistical package SPSS®. Results : In all the treatments of the variety INIVIT Y-93-4, the highest temperatures were obtained at 15 days after starting the ensiling process, with values of 27,0; 26,9 and 26,7 oC for T3, T1 and T2, respectively. However, the performance for the variety Señorita was different, with the highest temperature values (29,0 ºC) at the end of the process. Significant differences (p ≤ 0,001) were also found in the concentration of N-NH3 among the treatments in both varieties. The highest values (between 1,3 and 1,9) were obtained in T3, with regards to T1 and T2, which, in turn, differed between them. Conclusions : The silage fermentation dynamics, with different proportions of forage and root from M. esculenta of the variety INIVIT Y-93-4, reached adequate temperature, pH and N-NH3 parameters. The silages of both varieties did show good organoleptic characteristics.

RESUMEN Objetivo: Evaluar la calidad fermentativa y organoléptica de ensilajes con diferentes proporciones de forraje y raíz de dos variedades de Manihot esculenta Crantz en la provincia de Matanzas, Cuba. Materiales y Métodos: Se realizó un estudio en el laboratorio de nutrición de la Estación Experimental de Pastos y Forrajes Indio Hatuey, donde se evaluó la calidad fermentativa de dos variedades de M. esculenta (INIVIT Y-93-4 y Señorita), así como la calidad organoléptica del ensilado producido. Se aplicó un diseño completamente aleatorizado con tres tratamientos, donde cada variedad se evaluó por separado: T1) 0 % follaje: 100 % raíz; T2) 25 % follaje: 75 % raíz y T3) 100 % follaje: 0 % raíz, en cuatro momentos de evaluación. Se realizó análisis de varianza y para determinar la diferencia entre medias se utilizó la prueba de Duncan. Los datos se procesaron mediante el paquete estadístico SPSS®. Resultados: En todos los tratamientos de la variedad INIVIT Y-93-4, las temperaturas mayores se obtuvieron a los 15 días de iniciado el proceso de ensilado, con valores de 27,0; 26,9 y 26,7 oC para T3, T1 y T2, respectivamente. Sin embargo, el comportamiento para la variedad Señorita fue diferente, con los mayores valores de temperatura (29,0 oC) al final del proceso. También se encontraron diferencias significativas (p ≤ 0,001) en la concentración de N-NH3 entre los tratamientos en ambas variedades. Los mayores valores (entre 1,3 y 1,9) se obtuvieron en T3, con respecto a T1 y T2, los que, a su vez, difirieron entre ellos. Conclusiones: La dinámica de fermentación de los ensilajes, con diferentes proporciones de forraje y raíz de M. esculenta de la variedad INIVIT Y-93-4, alcanzó parámetros adecuados de temperatura, pH y N-NH3. Los ensilajes de ambas variedades sí presentaron buenas características organolépticas.

Abstract In order to characterize the fermentation dynamics of a silage of whole sorghum plant (Sorghum bicolor L. Moench) with inclusion levels of citrus fruit (Citrus sp.), pH, ammonia content and concentration of volatile fatty acids (acetic, propionic and butyric) were evaluated as quality indicators. A complete randomized design was applied with four treatments: a) 100 % sorghum, b) 75 % sorghum: 25 % pulp; c) 50 % sorghum: 50 % pulp, d) 25 % sorghum: 75 % pulp. Four moments were established (14, 28, 42 and 56 days) with six repetitions for each one. The silages showed pH between 3,29 and 4,32. A decrease of this indicator was observed, as the pulp percentage in the mixture increased. The silages with pulp reached the lowest pH values at 56 days of evaluation; while the sorghum silage (100 %) achieved them at 42 days. The ammoniacal nitrogen, just like pH, decreased with the inclusion of the pulp, and increased as the evaluation moments passed, with contents between 0,05 and 2,54 mg N-NH3 100 mL-1. With regards to the volatile fatty acids, acetic acid showed the highest concentrations in all the silages during the evaluation period, with values between 1,7 and 17, 2 mmole L-1. The quantities of propionic and butyric acid were negligible, and were in the range of 0,015 and 0,33 mmole L-1for propionic and 0,004 and 0,037 mmole L-1 for butyric. There were significant differences in the production of acetic and butyric acid among the treatments since day 28 of the evaluation. Propionic acid showed differences since day 42. It is concluded that the fermentation quality indicators are within the established range to classify silages as having good quality.

Resumen Para caracterizar la dinámica de fermentación de un ensilaje de planta entera de sorgo (Sorghum bicolor L. Moench) con niveles de inclusión de pulpa de cítrico (Citrus sp.), se evaluaron como indicadores de calidad el pH, el contenido de amoniaco y la concentración de ácidos grasos volátiles (acético, propiónico y butírico). Se aplicó un diseño completamente aleatorizado con cuatro tratamientos: a) 100 % sorgo, b) 75 % sorgo: 25 % pulpa; c) 50 % sorgo: 50 % pulpa, d) 25 % sorgo: 75 % pulpa). Se establecieron cuatro momentos (14, 28, 42 y 56 días) con seis repeticiones para cada uno. Los ensilajes mostraron pH entre 3,29 y 4,32. Se observó una disminución de este indicador, según aumentaba el porcentaje de pulpa en la mezcla. Los ensilajes con pulpa alcanzaron los valores más bajos de pH a los 56 días de evaluación, mientras que el de sorgo (100 %) lo logró a los 42 días. El nitrógeno amoniacal, al igual que el pH, disminuyó con la inclusión de la pulpa, y aumentó a medida que trascurrieron los momentos de evaluación, con contenidos entre 0,05 y 2,54 mg N-NH3 100 mL-1. Con respecto a los ácidos grasos volátiles, el acético mostró las mayores concentraciones en todos los ensilajes durante el período de evaluación, con valores entre 1,7 y 17, 2 mmole L-1. Las cantidades de ácido propiónico y butírico fueron despreciables, y estuvieron en el orden de 0,015 y 0,33 mmole L-1 para el propiónico y 0,037 y 0,004 mmole L-1 para el butírico. Hubo diferencias significativas en la producción de acético y butírico entre los tratamientos a partir del día 28 de evaluación. El propiónico mostró diferencias a partir del día 42. Se concluye que los indicadores de calidad fermentativa se encuentran en el rango establecido para clasificar los ensilajes de buena calidad.

Resumen El objetivo de este trabajo fue evaluar la calidad bromatológica, la degradación de la materia seca y el potencial mitigador de metano del forraje proveniente de diferentes arreglos silvopastoriles bajo tres niveles de sombra (0, 30 y 60%). Este estudio se llevó a cabo entre octubre de 2012 y setiembre de 2013 en la hacienda La Candelaria de la Universidad de Antioquia, Colombia. Para los arreglos se utilizaron gramíneas de género Brachiaria ( Brachiaria brizantha cv toledo, Brachiaria decumbens y Brachiaria hibrido cv mulato II) solas o asociadas con Tithonia diversifolia y Cratilya argentea en arreglo silvopastoril. La evaluación se realizó en el forraje de cuarenta días, se determinó la composición química, contenido de ácidos grasos poliinsaturados, degradación de la materia seca y producción de metano in vitro. El arreglo utilizado (gramínea sola o asociada a arbustiva) afectó significativamente la concentración de proteína y ácido linoleico (p<0,05). No se presentó efecto del arreglo, el nivel de sombra ni de la interacción arreglo x sombra sobre la degradación de la materia seca a las 48 h (p>0,05). Sin embargo, pruebas planeadas indicaron que al asociar Brachiaria brizantha cv toledo con las arbustivas, se mejoró la degradación de la materia seca (MS) a las 48 h y se observó que la interacción arreglo x sombra afectó la dinámica de esta. Los factores evaluados (arreglo y sombra) no influyeron en la emisión de metano in vitro.

Abstract The aim of this work was evaluate the bromatological quality, the degradability of dry matter and the mitigation potential of the forage from the different silvopastoral arrangements in three shade levels (0, 30 y 60%). This study was carried out between October 2012 and September 2013, in the La Candelaria farm from the Antioquia University, Colombia. The arrangements contained within Brachiaria grasses ( Brachiaria brizantha cv toledo, Brachiaria decumbens and Brachiaria hibrido cv mulato II) alone or associated with Tithonia diversifolia and Cratilya argentea in silvopastoral arrangements. Evaluation was made in forage of forty days, the chemical composition, content of polyunsaturated fatty acids, degradation of dry matter and in vitro methane production were determined. The arrangement used (grass alone or associated with shrubs affected significantly the concentration of protein and linoleic acid (p<0.05). Not effect was observed in the arrangement, level of shade and interaction arrangement x shade in the degradability of dry mater after 48 h (p>0.05). However, pre-planned comparisons indicated that the association of Brachiaria brizantha cv toledo with shrubs improved the degradability of dry matter (MS) at 48 h, and was observed that the interaction shade x arrangement affected the dynamic degradation of MS. The factors evaluated (arrangement and shade) did not affect the in vitro methane emission.

Se estudió la dinámica fermentativa in vitro de los forrajes pasto estrella (Cynodon plectostachyus; E), pasto guinea (Megathyrsus maximus; G) y leucaena (Leucaena leucocephala; L), disponibles en sistemas silvopastoriles intensivos (SSPi). Se recolectaron muestras en SSPi establecidos en bosque seco tropical en el Valle del Cauca, Colombia. Se realizaron 10 mezclas o tratamientos con diferentes porcentajes de inclusión: E100, G100, L100, E33G66, E66G33, L33E66, L66E33, L33G66, L66G33 y L33E33G33. El menor tiempo de fase Lag se observó con L100 (7,02 h) y E33G66 (7,11 h), menores (a = 0,05) a L33E66 (10,22 h) y G100 (9,85 h). Las producciones máximas de gas (a) variaron entre 97,34 y 253 ml/g sustrato para L100 y G100, respectivamente. El menor valor de HPI se obtuvo con L100 (23,3 horas) y el gas acumulado a ese punto fue 35,08 ml, que coincide con el valor más bajo. Los tratamientos de mayor acumulación de gas fueron los que incluyeron gramíneas solas o sus mezclas y los de menor acumulación de gas fueron los que incluyeron leucaena. En cuanto al FP, a las 24 horas de incubación los valores más altos se presentaron con L100 y en las mezclas que incluyeron leucaena. Se concluye que la inclusión de leucaena estuvo asociada a disminuciones en el tiempo de fase lag y tasas máximas de producción de gas, así como con altos valores de FP, características que pueden asociarse a mayor eficiencia en los procesos de fermentación.

Abstract A study of the in vitro fermentation dynamics of the forages star grass (Cynodon plectostachyus; E), Guinea grass (Megathyrsus maximus; G) and Leucaena leucocephala (L), available in intensive silvopastoral systems (ISS) was carried out. Samples of these forages were harvested in ISS set in tropical dry forest in the Valle del Cauca, Colombia. With these forages, ten mixes or different treatments were generated: E100, G100, L100, E33G66, E66G33, L33E66, L66E33, L33G66, L66G33 and L33E33G33. The shorter lag phase was observed with L100 (7.02 h) and E33G66 (7.11 h), lower (a= 0.05) than that of L33E66 (10.22 h) and G100 (9.85 h). The maximum production of gas (a) ranged between 97.34 and 253 ml/ g substrate for L100 and G100, respectively. The lowest HIP value was obtained with L100 (23.3 hours) and the gas accumulated to that point was 35.08 ml, which coincides with the lower value. The treatments that most accumulated gas were the grasses alone or their mixtures and those with the least accumulated gas included leucaena. Regarding FP, after 24 hours of incubation, the greater values occurred with L100 and mixtures that included leucaena. It is concluded that the inclusion of Leucaena was associated with decreases in the lag phase time and maximum gas production rates and with high values of FP, characteristics that may be associated with more efficient fermentation processes.

Resumo Estudou-se a dinâmica fermentativa in vitro das forrageiras do capim estrela (Cynodon plectostachyus; E), capim coloni ão (Megathyrsus maximus; G) e leucaena (Leucaena leucocephala; L), disponíveis em sistemas silvopastoris intensivos (SSPi). Tomaram-se amostras em SSPi estabelecidos em bosque seco tropical no Vale do Cauca, Colômbia. Realizaram-se 10 misturas ou tratamentos com diferentes porcentagens de inclus ão: E100, G100, L100, E33G66, E66G33, L33E66, L66E33, L33G66, L66G33 e L33E33G33. O menor tempo da fase Lag se observou com L100 (7,02 h) e E33G66 (7,11 h), menores (a = 0,05) a L33E66 (10,22 h) e G100 (9,85 h). As produções máximas de gás (a) variaram entre 97,34 e 253 ml/g substrato para L100 e G100, respectivamente. O menor valor de HPI obteve-se com L100 (23,3 horas) e o gás acumulado nesse ponto foi 35,08 ml, que coincide com o menor valor. Os tratamentos de maior acumulação de gás foram os que incluíram gramíneas solas ou suas misturas e os de menor acumulação de gás foram os que incluíram leucaena. Em quanto ao FP, as 24 horas de incubação os valores maiores apresentaram-se com L100 e em misturas que incluíram leucaena. Pode se concluir que a inclus ão de leucaena esteve associada a diminuições no tempo de fase lag e taxas máximas de produção de gás, assim como com altos valores de FP, características que podem-se associar com a maior eficiência nos processos de fermentação.

Objetivou-se com o presente estudo avaliar diferentes níveis (0, 20, 40 e 60%) de inclusão de erva-sal na dinâmica fermentativa da silagem de cana-de-açúcar. Utilizou-se delineamento experimental inteiramente casualizado com quatro tratamentos e seis repetições. Após 90 dias, com a abertura dos silos, determinou-se os teores de carboidratos solúveis (CHO-Sol), etanol, ácidos orgânicos (lático, acético, propiônico, butírico), proteína bruta (PB), matéria mineral (MM), matéria seca (MS), fibra em detergente neutro livre de cinzas (FDNc), pH e poder tampão (PT); estimou-se a perda total de MS, perdas por efluente e gases, densidade e a recuperação da MS. Os níveis crescentes de erva-sal propiciaram diminuição das perdas totais de MS e por efluente, aumento de seu teor e recuperação desta. As silagens apresentaram pH adequado à conservação (≤3,70) e concentração de minerais acrescidos. As concentrações de etanol foram influenciadas (P<0,05) pelo incremento de erva-sal, em que se observou redução de 51,84%, com 40% de erva-sal na silagem de cana. A adição de erva-sal reduz as perdas de MS e a produção de etanol e, melhora a qualidade fermentativa da silagem de cana-de-açúcar.

The objective of this study was to evaluate different inclusion levels (0, 20, 40 and 60%) of old man saltbush in the fermentation dynamics of sugarcane silages. The experiment was carried out as a completely randomized design with four treatments and six replicates. After 90 days, with the opening of the silos, the levels of water soluble carbohydrates, ethanol, organic acids (lactic, acetic, propionic, butyric acid), crude protein (CP), mineral matter (MM), dry matter (DM), neutral detergent fiber ash free (NDFa), pH and buffer capacity were determined; and, the losses by gas, effluent and total of dry mater, density and dry matter recovery were estimated. Increasing levels of saltbush propitiated reduction in losses: by effluent and total dry matter, it also increased the concentration and recovery. The silages showed pH suitable for conservation (≤3.70) and mineral concentration increased. The ethanol concentrations were influenced (P<0.05) by the increase of saltbush, where reduction of 51.84% was observed, with 40% saltbush in sugarcane silage. The addition of saltbush reduces dry matter losses and ethanol production and, improves the quality of sugarcane silage.

Objetivou-se com este estudo avaliar os efeitos de aditivos químicos na ensilagem de cana-de-açúcar sobre a dinâmica fermentativa e a composição química das silagens. O experimento foi desenvolvido em delineamento inteiramente casualizado, com cinco repetições. A cana-de-açúcar foi ensilada sem aditivo ou tratada com 1% (massa verde) de cal virgem ou calcário, constituindo três tratamentos. A dinâmica fermentativa foi analisada com base nas perdas gasosas, nos ácidos orgânicos, na produção de etanol e na composição química das silagens. As menores perdas gasosas foram observadas nas silagens com cal virgem ou calcário. As silagens tratadas com esses aditivos apresentaram maior teor de carboidratos solúveis residuais e de ácidos acético e butírico, além de reduzida fermentação alcoólica. As silagens com os aditivos químicos apresentaram, no momento da abertura, maior teor de cinzas e menor concentração de componentes fibrosos. O teor de proteína observado nas silagens está de acordo com a amplitude preconizada para a forragem in natura. A adição de cal virgem ou calcário no momento da ensilagem melhorou o padrão fermentativo das silagens, promovendo redução das perdas gasosas, inibição da fermentação alcoólica e maior quantidade de carboidratos solúveis remanescentes.

The objective of this study was to evaluate the effects of chemical additives on the fermentative dynamics and chemical composition of sugarcane silages. The experiment was conducted in a randomized complete design with five replications. Sugarcane was ensiled without additives or with calcium oxide and limestone (1% as-fed basis) constituing three treatments. The fermentative dynamic was analyzed based on gas losses, organic acids and ethanol production and, silages chemical composition. The calcium oxide and limestone treatments showed the lowest values of gas losses. Silages treated with these two additives also showed higher concentrations of water soluble carbohydrates, acetic and butyric acids, and low alcoholic fermentation. The treatments containing chemical additives presented the highest ash and the lowest fiber concentration. Crude protein for all treatments was in agreement with the values of fresh sugarcane. Calcium oxide or limestone addition at ensiling resulted in a better fermentative pattern, promoting reduction in gas losses, alcoholic fermentation inhibition, and high amounts of residual soluble carbohydrates.

Se desarrolló un experimento con Tithonia diversifolia, con diferentes edades de corte, para determinar el efecto de la edad en la capacidad fermentativa in vitro y en la dinámica de degradación ruminal in situ de su materia seca. Para el estudio in vitro se utilizaron tiempos de 0, 3, 6, 12, 24, 48, 72 y 96 h de fermentación, mientras que para la prueba in situ se realizaron muestreos a las 6, 12, 36, 48 y 72 h. Los resultados de la fermentación se ajustaron al modelo exponencial. El comportamiento cinético in vitro se caracterizó por un incremento de la producción de gases con el tiempo de exposición de las muestras al ataque de microorganismos, con valores de 36,03 32,12 34,12 37,11 y 34,7 a las 96 h para 30, 50, 70, 90 y 110 d de rebrote, respectivamente, con mayores valores en producción de gases a 90 h. La evolución en la dinámica de degradación ruminal in situ de la MS mostró un aumento progresivo de tipo asintótico, mientras que los valores de degradabilidad efectiva de MS para diferentes constantes de velocidad de recambio ruminal (k = 0,03 0,044 y 0,05 %/h) tuvieron un comportamiento similar en todos los nutrientes y oscilaron entre 46,39-60,46; 42,40-56,23; 41,75-53,86 y 41,18-53,31 para 30, 50, 70 y 90 d de rebrote, respectivamente. Los resultados obtenidos permiten sugerir, por los estudios in vitro e in situ, que edades entre 70 y 90 d son las que permiten un mayor aprovechamiento de los nutrientes por el animal. Estudios in vivo se hacen necesarios para avalar esta hipótesis, considerando diferentes niveles de inclusión de este arbusto en las dietas de los rumiantes.

An experiment was conducted with Tithonia diversifolia, at different harvesting ages to determine the effect of age on the in vitro fermentation capacity and on the in situ dry matter dynamic of ruminal degradation. For the in vitro study there were utilized incubation times of 0, 3, 6, 12, 24, 48, 72 and 96 h of fermentation, meanwhile for the in situ study, samplings were taken at 6, 12, 36, 48, and 72 h. Fermentation data were adjusted to the exponential model. In vitro kinetics performance showed an increment in the gas production as samples were exposed to attack of the microorganisms with values of 36.03, 32.12, 34.12, 37.11 and 34.7 at 98h for 30, 50, 70, 90, and 110 d of growing respectively, with higher values of gas production at 90 h. Dynamics of in situ dry matter ruminal degradation showed an asymptotic type of progressive increment, meanwhile data for dry matter effective degradability for different constants of ruminal turnover rate (k = 0.03, 0.044, and 0.05 %/h) had a similar performance in all nutrients, varying between 46.39-60.46, 42.40-56.23, 41.75-53.86, and 41.18-53.31 for 30, 50, 70, and 90d of growing, respectively. Results obtained suggested, according to the in vitro and in situ studies, that ages between 70 and 90d allow a great use of the nutrients by the animal. It is necessary to perform in vivo studies to confirm this hypothesis, considering inclusion of different levels of the plant in the diet of ruminants.

O experimento foi conduzido com o objetivo de avaliar a dinâmica fermentativa e microbiológica de silagens de capins tropicais acrescidas de polpa cítrica. Os capins tanzânia (Panicum maximum cv. Tanzânia) e marandu (Brachiaria brizantha (Hochst ex. A. Rich) Stapf cv. Marandu) foram colhidos aos 64 e 49 dias de rebrota, respectivamente, e ensilados com 0, 5 ou 10% de polpa cítrica peletizada (PCP), em relação à matéria verde, durante 1, 4, 7, 14, 21, 28 e 56 dias. Foram utilizados silos experimentais de PVC adaptados com válvula do tipo Bunsen para eliminação dos gases. A forragem foi compactada visando obter densidade de 550 kg/m³. O delineamento utilizado foi o inteiramente ao acaso com três repetições, em esquema de parcelas subdivididas. A inclusão de PCP aumentou os teores de MS e diminuiu o pH das silagens. A adição de PCP influenciou os teores de N-NH3 (N total), uma vez que, nas silagens sem PCP, os teores N-NH3 foram significativamente elevados, o que as caracteriza como de qualidade duvidosa. A adição de PCP aumentou a concentração molar dos ácidos acético e propiônico. A população de enterobactérias foi detectada somente no primeiro dia de fermentação nas silagens do capim-tanzânia e até o 18º dia nas do capim-marandu. Nas silagens avaliadas, a população de bactérias homofermentativas foi semelhante à das bactérias heterofermentativas.

The experiment was carried out to evaluate the fermentative and microbiological dynamics of the tropical grass silages using pelleted citrus pulp (PCP) as an additive. The Tanzania (Panicum maximum cv. Tanzania) and Marandu (Brachiaria brizantha (Hochst. ex. A. RICH) Stapf cv. Marandu) grasses were harvested at 64 and 49 days of regrowth, respectively. The following treatments were evaluated: control (0%), addition of 5% and 10% of pelleted citrus pulp (PCP) in a fresh matter basis, and seven fermentation periods (1, 4, 7, 14, 21, 28, and 56 days) after the ensilage. Experimental PVC silos with Bunsen valve to eliminate gas were used. The forage was compacted to obtain 550 kg/m³ of bulk density. It was used a split-plot arrangement in a complete randomized experimental design, with three replications per treatment. The addition of PCP increased the DM concentration and reduced the pH values of the silages. The concentration of NH3-N (total N) was affected by the PCP addition, and the absence of PCP resulted in silages with high N-ammonia concentration, which characterizes silages with questionable quality. The addition of PCP increased the molar concentration of the acetic and propionic acids. The enterobacteria population was detected only in the first day in the tanzaniagrass silage, and until the tenth eighth day of fermentation on the marandugrass silage. The homofermentative bacteria population was similar to the heterofermentative on the evaluated silages.

An experiment to study the characteristics of in vitro fermentation of forage was carried out in herbage mass samples (FD) and simulated grazing samples (FA), at two sward heights of a permanent pasture. The digestion kinetics of the forage was studied using in vitro gas production method. Data collected were fitted according to the equation of Orskov and McDonald. Gas production was greater (P<0.05) from herbage mass samples than simulated grazing samples at 12, 21, and 27 hours of incubation (161.7 v/s 150.6, s.e.d.= 4.23; 217.6 v/s 209.2, s.e.d.= 3.65; and 242.1 v/s 234.7, s.e.d.= 3.34, respectively). However, after 27 hours of incubation, no significant effect (P0.05) of type of sample, either on the amount of gas produced or on the kinetic of fermentation, were found. The dry matter disappearance after 96 hours of incubation was significantly lower (P<0.05) for herbage mass samples compared with simulated grazing samples (0.908 v/s 0.873, s.e.d.= 0.005), but with no effect of sward height (P0.05). These findings show the benefits of complementing in vitro gas production measurements with post digestion residue determinations to improve the knowledge on the nutritive value of feed fermented in the rumen

Se evaluó la dinámica fermentativa de forrajes, en muestras de una ID, manejada a dos alturas. Las muestras consistieron en forraje disponible a ras de suelo y en forraje aparentemente consumido (FA) por vacas lecheras en pastoreo continuo. La cinética de fermentación de los forrajes se estudió usando la técnica in vitro de producción periódica de gas, utilizando un mismo frasco de fermentación, de <A HREF="#THEODOROU 1994">Theodorou y col (1994)</A>. Los datos de producción acumulada de gas fueron corregidos a 1 g de materia seca, y fueron descritos ajustándolos a la ecuación exponencial de <A HREF="#ORSKOV 1979">Orskov y McDonald (1979)</A>. La producción de gas acumulada (ml/g) fue mayor (P<0.05) para el FD a ras de suelo que para el FA consumido para las 12, 21, y 27 horas de incubación (161.7 v/s 150.6 , s.e.d.= 4.23 ; 217.6 v/s 209.2, s.e.d.= 3.65; y 242.1 v/s 234.7, s.e.d.= 3.34, respectivamente). Después de 27 horas de incubación, no se detectó ningún efecto significativo entre FD y el FA (P0.05) en la cantidad de gas producido ni en la dinámica fermentativa de estos forrajes. Sin embargo, la digestibilidad de la materia seca (g/r) para el FD a ras de suelo, fue significativamente menor (P<0.05) que en el FA consumido medido a las 96 horas de incubación (0.908 v/s 0.873, s.e.d.= 0.005), pero sin efecto de la altura de pradera (P0.05). Estos resultados evidencian el beneficio de complementar el registro de la producción acumulada de gas in vitro con el análisis de los constituyentes del gas fermentado y con determinaciones de residuos de la digestión, a fin de mejorar el entendimiento del proceso fermentativo a nivel ruminal