Effects of ensiling on in situ ruminal degradability and intestinal digestibility of corn forage.

The effective degradability of dry matter (DM), crude protein (CP) and amino acids (AA), and the intestinal effective digestibility (IED) of DM and CP of a green forage corn (GC) and its silage (EC) were determined on freeze-dried samples using three rumen and duodenum cannulated wethers. Two rumen incubations with duplicate bags were performed for each feed. Rumen degradation was determined on one series of bags from each incubation. The other series was freeze-dried and used to determine IED using mobile nylon bags. Microbial contamination of rumen incubated residues (determined with 15N techniques) fitted exponential functions, which showed a greater microbial contribution in EC than in GC in the undegradable DM (18.6% vs. 13.5%) and CP (81.7% vs. 69.4%). Degradability was calculated considering the particle rumen outflow rate (k(p): 0.056/h) of the EC (EDp) or additionally the rate of comminution and mixing (kr: 0.130/h) of these particles (EDep). Ensiling increased EDp (9.33%, p < 0.01) or EDcp (5.30%, p = 0.062) of DM and was associated with losses of nitrogen and with large changes in the AA profile. It is necessary to correct the microbial contamination, because it represents 32.0% (GC) and 42.5% (EC) of the undegraded CP when using k(p) and k(c). Ensiling caused higher degradabilities for some AA as well as large differences in the changes due to the rumen fermentation on the AA profile. However, it had only limited effects on the undegraded protein profile. Ensiling also reduced the IED of DM (23.3% vs. 14.6%; p = 0.057). In conclusion, results do not show losses of nutritive value by ensiling corn cut at vitreous grain stage.

Efecto del aplazamiento de utilización sobre el contenido de nutrientes y digestibilidad de la matería orgánica de la asociación buffel-leucaena / Effect of deferment of utilization on the nutrient content and organic matter digestibility of buffel-leucaena association

En una región semiárida del Estado Zulia, Venezuela (10°32'N, 71°42'0), con 600mm de precipitación promedio anual y suelos de textura franco-arenosa, pH 5,5 con valores de Ca, Mg, Na, K y P de 0,6; 0,3; 0,1 y 0,17 mg/100 g de suelo y 6 ppm, respectivamente, se estudió el efecto de cuatro edades de utilización (42,84,126, y 168 días) sobre el contenido de proteína cruda (PC), digestibilidad in vitro de la matería orgánica (DIVMO) y minerales de una asociación buffel (Cenchrus ciliaris)-leucaena (Leucaena leucocephala). Muestras compuestas de hojas y tallos para buffel y fracción fina (pinna, pecíolos y tallos <5mm de diámetro) en leucaena se analizaron para DIVMO y contenido de PC, Ca, P, Mg, K y Na. El diseño experimental usado fue de bloques al azar con tres repeticiones. En buffel, PC (8,66 por ciento) y K (3,65 por ciento) resultaron adecuados para rumiantes a pastoreo, mientras que Ca, P, Mg, y Na fueron deficientes. En leucaena, PC, Ca, Mg, y K resultaron adecuados, mientras el P y Na estuvieron por debajo del nivel crítico de deficiencia. Solo el Na incrementó (P<0,05) con el aumento de la madurez.

In situ intestinal digestibility of dry matter and crude protein of cereal grains and rapeseed in sheep.

The ruminal degradation and intestinal digestibility (ID) of dry matter (DM) and crude protein (CP) of different feed samples were measured in two trials by using nylon bag and rumen outflow rate techniques in three wethers cannulated in the rumen and in the duodenum. In trial 1, three samples of grains of wheat, barley, and corn treated by cooking (TW, TB, and TC, respectively) were studied together with a sample of untreated corn grains (CG) of different origin. In trial 2, these studies were carried out on a sample of rapeseed (RS) and on a mix of this same sample and rapeseed meal (in proportions 70:30) treated by cooking (TR). In both trials, the animals were fed at the same intake level (40 g DM x kg(-1) LW0.75) with 2:1 (DM basis) forage to concentrate diets. Rumen degradation rates of DM were high in the treated cereals (between 11.0 and 14.2% x h(-1)) and low in the CG (6.35% x h(-1)), whereas for CP these rates were low in all cereals. For DM, in all cereals, ID decreased linearly as the ruminal incubation time increased. The values of intestinal effective digestibility (IED), calculated from these functions and from the rumen outflow, were respectively: 86.4, 62.1, 51.5, and 67.9%. For CP, ID was unaffected by the ruminal incubation time in corn samples, whereas in TW and TB a reduction of these values was only observed for the time of 48 h. The values of IED of CP for CG, TW, TB and TC were: 82.6, 88.9,82.5, and 91.6%, respectively. Rumen degradation rates of the RS and TR samples were 8.35 and 8.23% x h(-1) for DM and 12.0 and 9.59% x h(-1) for CP. In RS, the ID of DM and CP showed a downward trend with an increase of the ruminal incubation time, as modelled according to an exponential function. This same trend was observed for TR after a lag period estimated at 7.53 and 6.51 h for DM and CP, respectively. The values of IED of RS and TR were respectively 56.5 and 50.8% for DM and 71.9 and 80.1% for CP. These same results were also determined by a simplified method using a sample pooled to be representative of the rumen outflow of undegraded feed. The respective values for RS and TR were 54.8 and 51.6 for DM and 65.8 and 78.9% for CP. This method seems to be a promising technique to estimate IED, although more studies are needed to improve its accuracy.

Evaluación de cinco accesiones de centrosema pubescens para la alimentación de bovinos en un bosque húmedo tropical / Evaluation of five accessions of centrosema pubescens in cattle feeding programs in wet tropical forests

En la zona de El Guayabo, al Sur del Lago de Maracaibo, Estado Zulia, Venezuela. Se realizó un experimento con el fin de comparar la digestibilidad in vitro de la materia orgánica (DIVMO) y los contenidos de proteína cruda (PC) y minerales (macro y microelementos) de cinco accesiones de centrosema pubescens (N° CIAT 5167, 5169, 15150, 15154 y 15160). Las accesiones fueron sembradas por surcos en parcelas de 7,5/m² con 10 plantas por accesión y 2 m entre surcos en un suelo franco limoso con pH 6,6 y 1,6 por ciento de MO, bajo condiciones de Bosque Húmedo Tropical. La altura de corte fue a 10 cm sobre el suelo y el área de muestreo de 0,5/m². Se utilizó el forraje proveniente de dos cortes, uno durante el período de máxima precipitación (1150mm) y otro en el de mínima precipitación (673mm). La edad del material era de nueve semanas en cada período. El diseño experimental fue de parcelas divididas en el tiempo en bosques al azar con 2 repeticiones, considerando las accesiones como parcelas principales y los períodos como subparcelas. No se detectó efecto (P>0,05) de las accesiones, ni de los períodos ni de su interacción sobre ninguna de las variables estudiadas. Los valores medios obtenidos fueron: DIVMO, 53,6 por ciento; PC, 24,1 por ciento; macroelementos: 1,11 por ciento Ca; 0,34 por ciento P; 0,27 por ciento Mg; 1,50 por ciento K y 0,018 por ciento Na; microelementos: 238 ppm Fe; 57,9 ppm Mn; 35,0 ppm Zn; 17,9 ppm Cu; 0,09 ppm Co, 0,71 ppm Mo y 1,02 ppm Se. Desde el punto de vista de la nutrición animal, el Na resultó deficiente en todas las muestras, mientras que la mayoría de las accesiones presentaron niveles adecuados de microelementos excepto al N° 15150 para Mn, y las N° 15150 para Mn, y las N° 15150 y 15154 y 15160 para Co. No se detectaron niveles tóxicos para ninguno de los elementos estudiados. Las accesiones evaluadas mostraron valores similares en términos de digestibilidad in vitro, proteína cruda, macro y microelementos