TY - JOUR

T1 - Application of non-linear models in the description of in situ degradation profiles of the elephant grass (Pennisetum purpureum Schum., Mineiro variety)

AU - Vieira, Ricardo A.M.

AU - Pereira, José C.

AU - Malafaia, Pedro A.M.

AU - De Queiroz, Augusto C.

N1 - Funding Information: The authors wish to thank the Conselho National Cientifico e Tecnologico (CNPq) and the Coordenadoria de Nivel Superior (CAPES) for financial support.

PY - 1997/5

Y1 - 1997/5

N2 - Degradation profiles of dry matter (DM), crude protein (CP) and neutral detergent fiber (NDF) from elephant grass, Mineiro variety, cut and collected at different ages after planting, were obtained by in situ trials using three rumen cannulated Holstein heifers. Models derived from the exponential decay law and the first-order reaction curve, as well as logistic models (compartmental models of digestion), were used to describe the incubation data, with the curve-fitting of the various models compared through the examination of the residuals (ê1 = Yi-Ŷi). The time profiles of the natural logarithm of the insoluble but potentially degradable residue were analyzed by decomposing the mean square of the independent variable (time) in its polynomial effects. Results showed that 56% of the fractions that compose the nutrients were homogeneous; some profiles presented a quadratic fit, indicating the presence of a lag phase in its initial portion. The cubic effect observed indicated non-homogeneity of the pool, suggesting modifications of the first-order model for a correct kinetic interpretation. The lower number of runs of sign of the residuals revealed the tendency of the first-order exponential models to over-or underestimate certain degradation profiles sections, principally the model whose parameters were estimated after logarithmic transformation and linear regression of the data. The fitting of the compartmental model of digestion and the compartmental model of digestion corrected for the discrete lag time resulted in greater stability and greater number of runs of sign of the residuals, and both models did not show a significant lack of fit test for any curve. It was necessary a reparameterization of the digestion compartmental model in order to fit 42.22% of the degradation profiles studied. These models seems to describe adequately the data for in situ incubation of elephant-grass; however, no long lag times were observed, and the correction for the discrete lag seems not to be necessary. If a sigmoidal pattern is followed, the compartmental model of digestion should be used in the description of degradation profiles of nutrients found in other tropical forages. As a consequence, it could also be used to calculate the ruminal availability and the escape of dietary nutrients to the lower tract.

AB - Degradation profiles of dry matter (DM), crude protein (CP) and neutral detergent fiber (NDF) from elephant grass, Mineiro variety, cut and collected at different ages after planting, were obtained by in situ trials using three rumen cannulated Holstein heifers. Models derived from the exponential decay law and the first-order reaction curve, as well as logistic models (compartmental models of digestion), were used to describe the incubation data, with the curve-fitting of the various models compared through the examination of the residuals (ê1 = Yi-Ŷi). The time profiles of the natural logarithm of the insoluble but potentially degradable residue were analyzed by decomposing the mean square of the independent variable (time) in its polynomial effects. Results showed that 56% of the fractions that compose the nutrients were homogeneous; some profiles presented a quadratic fit, indicating the presence of a lag phase in its initial portion. The cubic effect observed indicated non-homogeneity of the pool, suggesting modifications of the first-order model for a correct kinetic interpretation. The lower number of runs of sign of the residuals revealed the tendency of the first-order exponential models to over-or underestimate certain degradation profiles sections, principally the model whose parameters were estimated after logarithmic transformation and linear regression of the data. The fitting of the compartmental model of digestion and the compartmental model of digestion corrected for the discrete lag time resulted in greater stability and greater number of runs of sign of the residuals, and both models did not show a significant lack of fit test for any curve. It was necessary a reparameterization of the digestion compartmental model in order to fit 42.22% of the degradation profiles studied. These models seems to describe adequately the data for in situ incubation of elephant-grass; however, no long lag times were observed, and the correction for the discrete lag seems not to be necessary. If a sigmoidal pattern is followed, the compartmental model of digestion should be used in the description of degradation profiles of nutrients found in other tropical forages. As a consequence, it could also be used to calculate the ruminal availability and the escape of dietary nutrients to the lower tract.

KW - Digestion kinetics

KW - Elephant-grass

KW - Mathematical models

KW - Rumen

KW - Tropical forages

UR - http://www.scopus.com/inward/record.url?scp=0042131796&partnerID=8YFLogxK

U2 - 10.1016/S0377-8401(96)01100-5

DO - 10.1016/S0377-8401(96)01100-5

M3 - Journal article

AN - SCOPUS:0042131796

VL - 66

SP - 197

EP - 210

JO - Animal Feed Science and Technology

JF - Animal Feed Science and Technology

SN - 0377-8401

IS - 1-4

ER -