Nutritional Value of two Native Shrub Species That Grown in the Tamaulipan Thornscrub from

Introduction Rangeland owners use native foliage of trees and shrubs species during dry periods, for feeding livestock as green forage, fruits and litter fall. Shrub species of the Fabaceae family, particularly A. amentacea and P. texana are part of the dominant species at northeastern Mexico (Estrada-Castillon and Jurado, 2005). These species are characterized by having foliage throughout the year, with enough contents of CP and DM for facing the demands of small ruminants grazing in different physiological conditions (Ramirez and Gonzalez, 2010); moreover, these tannins-rich species have an agronomic advantage over the non tannincontaining plants in their adaptation to biotic and environmental stresses (Getachew et al., 2000). Studies performed with the gas production technique are of special interest since they provide kinetic information of the fermentation and are more efficient than other procedures in evaluating the effects of tannins and other anti-nutritive factors (Makkar, 2003). The addition of binders such as polyethylene glycol (PEG) has been used in order to decrease the tannin activity in plants and as an alternative to improve the quality of fodder; then, an increase of in vitro gas production indicate the effect on the activity of tannins in feeds (Getachew et al., 2000). Despite the diversity of floristic, ecological, biological and physiological studies developed about native plants in arid and semiarid regions, only sparse information exists on the nutritive value of shrubby species grown in the Tamaulipan scrubland. The objectives of this paper were to estimate the chemical composition and fermentation kinetics of the two shrubby species and in what extent these species can meet the nutritional requirements of ruminants managed in extensive systems. Material and Methods Study site and sampling This study was carried out at county sites Los Ramones, China and Linares, located in the state of Nuevo Leon in northeastern Mexico. The sites have been previously described by Gonzalez-Rodriguez et al. (2010). Monthly collection (2009) of mature leaves was undertaken (800 g), at browsing height (1.0-1.5 m) from the 5 most representative individual plants randomly selected of the shrub species A. amentacea, and P. texana. Samples were collected from 3 experimental plots (50 m x 50 m) established in each site. Once the samples were dried, at room temperature, leaves were grounded using 1 mm x 1 mm mesh, and stored in labeled plastic containers. Chemical composition The crude protein (CP#954.01), ether extract (EE; #929.29) and organic matter (OM#942.05), contents were determined as described by AOAC (1997). The neutral detergent fiber (NDFom) was completed following Van Soest et al. (1991). The condensed tannins (CT) were determined using butanol/HCl (95:5 v/v) and ferric ammonium sulfate (20 g/L 2N HCl) as reagents and leucocyanidin (1 mg/mL aqueous acetone, 700 mL/L) as standard. Absorbance was measured at 550 nm (Makkar, 2003). In vitro fermentation Five incubation runs were conducted for each sample within each shrub species with three repetitions. The rate and extent of in vitro gas production (GP) from shrub foliage were obtained from a 96 h incubation