A comparison of the prediction of apparent metabolisable energy content of starchy grains and cereal by-products for poultry from its chemical components, in vitro analysis or near-infrared reflectance spectroscopy

Abstract

Regression models including chemical composition, in vitro digestibility and near infrared reflectance spectroscopy (NIRS) were compared in order to predict the energy value of several feed ingredients for poultry. The nitrogen-corrected apparent metabolisable energy content (AMEn) in cockerels and its proportion on total gross energy (AMEn/GE) were determined in 94 batches from six starchy grains and six cereal byproducts. Two preliminary trials were also designed to adapt in vitro methods for prediction of in vivo energy values for poultry. Mean concentrations of AMEn of the ingredient studied ranged from 2,464 to 3,595 kcal kg ResumenComparación de la predicción de la concentración en energía metabolizable aparente de granos ricos en almidón y subproductos de cereales para aves a partir de componentes químicos, análisis in vitro o espectroscopía de reflectancia en el infrarojo En este trabajo se compararon varios modelos de regresión basados en parámetros de composición química, digestibilidad in vitro y en la espectroscopía de reflectancia en el infrarrojo cercano (NIRS) al objeto de predecir el valor energético de varios ingredientes alimenticios para aves. La concentración en energía metabolizable aparente corregida por nitrógeno (EMAn) en gallos adultos y su proporción sobre energía bruta (EMAn/EB) se determinaron en 94 partidas de seis concentrados de almidón y en seis subproductos de cereales. Dos ensayos preliminares fueron realizados para adaptar los métodos in vitro a los valores energéticos in vivo obtenidos en aves. Las concentraciones medias de EMAn de los ingredientes estudiados oscilaron entre 2.464 y 3.595 kcal kg -1 MS y las de EMAn/EB entre 53,7 y 80,0%. El modelo más preciso de predicción de los valores de EMAn y EMAn/EB fue el basado en ecuaciones NIRS (R 2 cv = 0,823 y 0,861, respectivamente). El mejor predictor químico de estos valores energéticos fue la concentración en FND de los ingredientes (R 2 = 0,616 y 0,736, respectivamente). La inclusión adicional de los contenidos en extracto etéreo y cenizas en el modelo EMAn y los de almidón y extracto etéreo en el de EMAn/EB permitieron incrementar los coeficientes de determinación hasta 0,791 y 0,839, respectivamente. Un modelo incluyendo los efectos lineales y cuadráticos de la digestibilidad de la materia orgánica in vitro (dMOIV) dio lugar a una predicción similar de los valores de EMAn/EB (R 2 = 0,833). Sin embargo, la predicción de EMAn a partir de dMOIV fue peor (R 2 = 0,62), puesto que las variaciones entre partidas de la concentración en EB (desde 4.225 hasta 5.896 kcal kg -1 MS) estuvieron escasamente relacionadas con los valores de digestibilidad in vitro. Palabras clave adicionales: concentración energética, eficacia energética, gallos adultos, modelos de predicción, NIRS.

Proving a concept: An in vitro approach

“…These authors correlated the in vitro starch degradation rate (modified assay from [14]) in 12 feedstuffs with the in vivo jejunal and ileal starch digestion in broiler chickens, showing that a 2-h incubation correlated well with the jejunal starch degradation, whereas a 4-h incubation correlated with the ileal starch degradation (Figure 4). Their data seem conflicting with losada et al [11], who showed a lower in vitro organic matter digestibility in corn compared with wheat after short incubation times ( Figure 2). However, this observation might be related to corn characteristics (amylopectin-to-amylase ratio), as a slower in vitro starch degradation rate from waxy corn compared with normal corn was shown [3].…”

“…In the first digestion step, samples were incubated with pepsin at pH 2, 39°C, over 2 h. The second step was incubation with pancreatin (protease, amylase, and lipase) at pH 6.8 and 39°C over 4 to 19 h. Finally, a third step was introduced using microbial carbohydrases (Viscozyme 120l [12]) at pH 4.8 and 39°C to simulate hindgut fermentation. The in vitro assay was calibrated with individually housed adult roosters fed mash diets near maintenance level [11]. Results (given in Figure 2) showed that the 2-step assay, using a 7-h incubation period with pancreatin, gave a good estimate of the relative in vivo AME n value of wheat, being 95% of the value of corn [11].…”

“…The relationship between the in vitro digestible energy content in the in vivo AME n values as measured in mature roosters [10]. The additional effect of an incubation with microbial enzymes is indicated (third step) [11]. Figure 3.…”

“…Recently, a 2-and 3-step in vitro assay, which was developed for pigs [9], was compared with estimates for digestibility of oM in wheat and corn [11]. In the first digestion step, samples were incubated with pepsin at pH 2, 39°C, over 2 h. The second step was incubation with pancreatin (protease, amylase, and lipase) at pH 6.8 and 39°C over 4 to 19 h. Finally, a third step was introduced using microbial carbohydrases (Viscozyme 120l [12]) at pH 4.8 and 39°C to simulate hindgut fermentation.…”

“…The in vitro assay was calibrated with individually housed adult roosters fed mash diets near maintenance level [11]. Results (given in Figure 2) showed that the 2-step assay, using a 7-h incubation period with pancreatin, gave a good estimate of the relative in vivo AME n value of wheat, being 95% of the value of corn [11]. It should be noted that this relative value in broilers generally is only 90% , indicating an overestimation of the feeding value of wheat in adult roosters.…”