Mechanistic Model Evaluation of Tree Species and Cactae Commonly Consumed by Grazing Goats

Abstract

Vargas-Villamil, L., Juárez-Reyes, A.S., Ku-Vera, J., Ávila-Vales, E., Vargas-Villamil, F., Medina-Peralta, S. and Cerrillo-Soto, M.A. 2008. Mechanistic model evaluation of tree species and cactae commonly consumed by grazing goats. J. Appl. Anim. Res., 33: 193–198. The mechanistic dynamic model, Kóokay, was used to estimate the initial high degradable phase (QS sc (0)), the medium degradation fractional rate (k ND,NDSm), the fermentation fractional rate (kSm,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 Qsc(0), k ND,NDSm and k Sm,SmF than tree leaves. The fΔG,ΔF > 40 mLG(mgF)−1 for Q. grisea and Opuntia spp and fΔG,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 kSm,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. schaffheri are similar, but lower than Opuntia spp and O. leptocaulis.