Two experiments using the Cornell Net Carbohydrate and Protein System were conducted to characterize the carbohydrate and protein fractions and corresponding rates of digestion of 15 tropical pasture grasses and to evaluate their ability to support milk production by dual-purpose cows. In the first experiment, ranges in carbohydrate and protein fractions of 15 grasses at 35 to 42 d of regrowth were: neutral detergent fiber (NDF) 63.5 to 74.9% of DM; permanganate lignin 4.7 to 7.8% of NDF; CP 5.5 to 11.9% of DM; and soluble protein 15.1 to 44.1% of crude protein (CP). The ranges of rates of digestion expressed as percent per hour were neutral detergent solubles (7.5 to 27.4); NDF (3.8 to 8.4); and neutral detergent insoluble protein (2.9 to 9.5). Predictions of the amount of milk that could be produced based on the amount of metabolizable energy supplied by the diet decreased 35% when NDF increased from 60 to 80%, and increased 88% when the rate of digestion of NDF increased from 3 to 6%/h. The milk production that could be sustained based on metabolizable protein in the diet doubled as CP increased from 4 to 12%. In the second experiment, nitrogen fertilization reduced NDF 7.3% and increased CP 84% without changing protein solubility, resulting in increased rumen nitrogen and metabolizable protein balances. With all forages, the Cornell Net Carbohydrate and Protein System predicted that availability of metabolizable protein would limit milk production. Predicted microbial growth was limited by ruminally available protein rather than by available carbohydrate.
Constantemente los forrajes deben realizar procesos de adaptación a los diferentes cambios en los factores ambientales lo cual conlleva a que sus variables fisiológicas se vean afectadas. El objetivo fue evaluar el comportamiento fisiológico de siete especies forrajeras tropicales en diferentes condiciones ambientales durante 2019 en Palmira, Colombia. Se implementó un diseño de bloques completos al azar, en tres localidades con diferentes altitudes, con cuatro repeticiones por especie para un total de 28 unidades experimentales por localidad. Se utilizó un analizador de medición fotosintético portátil Lcpro+, para la toma de datos de la tasa de fotosíntesis, conductancia estomática, tasa de transpiración y CO2 interno. Los datos recolectados fueron analizados mediante una comparación de medias con la prueba de Duncan (p≤ 0.05). Los indicadores fisiológicos de la especie Estrella, Kikuyo y la leguminosa Centrosema molle en las tres altitudes y las dos épocas demostrarían los mecanismos de adaptación que estas desarrollan en lugares adversos a los que se establecen.
Nota de investigación In vitro ruminal degradation of neutral detergent fiber insoluble protein from tropical pastures fertilized with nitrogen Degradación ruminal in vitro de la proteína insoluble en fibra detergente neutro de pastos tropicales fertilizados con nitrógeno Francisco Indalecio Juárez Lagunes a*
Our goal was to determine the digestion rates of carbohydrate fractions A (sugars, oligosaccharides and organic acids), B1 (starch and soluble fiber), NSC (non-structural carbohydrates) and B2 (available NDF) in four tropical grasses using the gas production technique. Samples of whole forage (WF), residue insoluble in 90% ethanol (EIR) and isolated NDF (ND) were fermented in vitro and gas production measured. Gas volumes determined from the following fractions, A = WF minus EIR; B1 = EIR - ND; NSC = WF - ND; and B2 = ND. Grasses were Andropogon gayanus, Urochloa brizantha, Cynodon plectostachyus, and Megathyrsus maximum each grown in Veracruz, Mexico on four plots (5×5 m), fertilized (relationship equivalent to 0 and 100 kg N/ha) and clipped 35 d after the N fertilization. A complete randomized block design with factorial arrangement 4×2 and two replicates per treatment was used. Factors were grass species and N fertilization. Data were fit using a single-pool exponential model with lag. The volume (mL gas/100 mg OM), rate (%/h) and lag (h) were: WF (22.8; 5.3; 2.1); A (3.2; 15.7; 0.5); B1 (1.5; 15.7; 0.2); and B2 (18.3; 6.6; 5.2). Andropogon and Urochloa had higher NSC content compared to Megathyrsus and Cynodon but lower gas yield per unit of NSC. Rates of digestion for the B2 fraction ranged from 4 to 8 %/h; and NSC digestion rate averaged 15.7 %/h. Nitrogen fertilization reduced carbohydrate pool sizes but did not affect rates of digestion. It is concluded that ruminally available energy from SC and NSC in tropical forages should be revised more extensively.
El objetivo fue desarrollar modelos de calibración de espectroscopia de reflectancia en el infrarrojo cercano (NIRS) para estimar el contenido de las fracciones de fibra y de carbohidratos en pastos Urochloa sp. para la zona tropical de México. Ciento ochenta y nueve muestras de tres híbridos de Urochloa fueron cosechadas cada 35 días durante un año, las cuales fueron analizadas por química húmeda para las fracciones de fibra: Fibra Detergente Neutra (NDF), Proteína insoluble en Detergente Neutro (NDIP), Fibra Detergente Ácida (ADF), Proteína Insoluble en Detergente Ácido (ADIP) y Lignina (LIG), y se estimaron los carbohidratos totales (TC), carbohidratos fibrosos (FC), carbohidratos no fibrosos (NFC) y carbohidratos indigestibles (UC). Los modelos de calibración y de validación se evaluaron por los respectivos Coeficientes de Determinación (R2); Errores Estándar de Validación Cruzada (SECV); y la desviación residual de la predicción (RPD). Además, con un conjunto de muestras externas, se realizó una prueba de sensibilidad evaluada por el Cuadrado Medio del Error de Predicción (MSPE). Las calibraciones obtenidas presentaron un adecuado ajuste y eficiencia predictiva mediante espectrofotometría NIR para NDF (RPD 2.4) y TC (RPD 2.5) lo que demuestra confiabilidad y capacidad de predicción para estas fracciones. Sin embargo, LIG, FC, NFC y UC requieren más observaciones para acrecentar su confiabilidad.
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