Comparison of two mathematical models in the description of in situ degradability

Villela Savian, Tacianal, Joel, Joel, JoelHenrique de Aquino, LuizFurtado Ferreira, Daniel

With the purpose of comparing the ruminal degradation models, proposed by Waldo et al. (1972) and Mertens and Loften(1980), the data of in situ degradability were employed. The experiment evaluated the potentially degradable residue of neutraldetergent fiber (NDF) of grass Tifton 85 (Cynodon spp) submitted to twelve cutting ages (30, 60, 90, 120, 150, 180, 210, 240,270, 300, 330 and 360 days), in a randomized block design with three replicates. At each cutting age, NDF degradation wasinvestigated by utilizing nine incubation times (0, 3, 6, 12, 24, 48, 72, 96 and 120 hours). The analysis was done by taking intoaccount a strip experiment and the factors studied were cutting ages and the incubation times of the grass. Each plot compriseda non-lactating cow, with a permanent ruminal fistula. The quality of the fit of each model was evaluated by the respective fitteddetermination coefficients, test for lack of fit and also the variances of the estimators of the parameters, by proposing expressionsfor estimate of the confidence interval for the parameters of the models. The results showed a better fit of the model by Waldo etal. (1972) to the data of neutral detergent fiber of grass Tifton 85.

1. degradability model, fit quality, non-linear regression, colonization time