INFLUENCIA DEL POLIETILÉN GLICOL SOBRE LOS PARÁMETROS DE PRODUCCIÓN DE GAS in vitro EN CUATRO FORRAJERAS NATIVAS CONSUMIDAS POR EL VENADO COLA BLANCA POLYETHYLENE GLYCOL INFLUENCE ON in vitro GAS PRODUCTION PARAMETERS IN FOUR NATIVE FORAGES CONSUMED BY WHITE-TAILED DEER

The chemical composition and the in vitro fermentation in leaves, treated with or without polyethylene glycol (PEG), of native shrub from northeastern Mexico, such as: Acacia amentacea, Celtis pallida, Forestiera angustifolia and Parkinsonia texana were established. These shrubs were gathered from fields without any disturbance. Leaves were collected at two sampling times (January and April, 2009) in three municipalities (China, Linares and Los Ramones) of the state of Nuevo Leon, Mexico. A wide range in chemical composition and in vitro gas production kinetics was observed among sites, species and sampling times of each species. A. amentacea (CT = 18 %) and P. texana (8 %), which had a higher condensed tannins content (CT), significantly increased the in vitro gas production parameters and the metabolizable energy after a treatment with PEG. Celtis pallida had the highest in vitro fermentation parameters due to the lower levels of lignin (ADL) and CT. Some variation was observed among shrubs such as in F. angustifolia that had lower fermentation and lower ADL and CT. This discrepancy could be due to genotypic characteristics relative to the type of plant secondary compounds activity. All plants resulted with high nutritional value for white-tailed deer knowing that deer have digestive mechanisms to neutralize CT. PALABRAS CLAVE: Acacia amentacea, Celtis pallida, Fo- restiera angustifolia, Parkinso- nia texana, composicion quimi- ca, fermentacion ruminal.