Mechanistic Model Evaluation of Tree Species and Cactae Commonly Consumed by Grazing Goats^a,^b

The mechanistic dynamic model, Kóokay, was used to estimate the initial high degradable phase (Q_SC(0)), the medium degradation fractional rate (k_ND,NDSm), the fermentation fractional rate (k_Sm,SmF) and the relation between the produced gas as a function of the fermented mass (f_ΔG,ΔF). To obtain these parameters a bounded regression problem was solved using in situ and in vitro data. It was found that: the cactae had much higher value for Q_SC(0), k_ND,NDSm and k_Sm,SmF than tree leaves. The f_ΔG,ΔF > 40 mLG(mgF)⁻¹ for Q. grisea and Opuntia spp and f_ΔG,ΔF < 40 mLG(mgF)⁻¹ for the others. At the incubation time of 8 h, the fermentation of the tree leaves, the O. leptocaulis and the Opuntia spp was 20, ∼35 and 60 mgF (100 mgDM)⁻¹, respectively. It was concluded that k_Sm,SmF is an important parameter to determine the nutritive value of new feeds since it is useful to predict the F into the rumen. Also, the F for Q. grisea, Q. eduardii and A. schaffneri are similar, but lower than Opuntia spp and O. leptocaulis.