Seasonal variation of chemical composition and crude protein digestibilityin seven shrubs of NE Mexico

The in situ digestibility of crude protein (CP) and effective degradability of CP (EDCP) in leaves of seven browse species growing in northeastern Mex ico are reported. Leaves of Acacia berlandieri, Acacia greggii, Acacia rigi dula, Cercidium macrum, Desmanthus virgatus, Leucaena leucocephala and Zizy phus obtusifolia were collected during summer (September 12, 1992), fall (N ov 12, 1992), winter (Feb 20, 1993), and spring (May 22, 1993) tin Marin, C ounty, Nuevo Leon, Mexico. Medicago sativa hay was used for comparison. Twe lve rumen cannulated male (Pelibuey x Rambouillet) sheep (45 kg BW) were us ed (4 sheep per plant species) to incubate nylon bags (5x10 cm; 53 mm pore size), each containing 4 g of ground material (1 mm screen). Bags were incu bated for 0, 4, 8, 12, 24 and 48 h. EDCP values were high in winter and spr ing, but low in summer and fall. Plants such as C. macrum (63% annual mean) , L. leucocephala (64%), D. virgatus (60%), A. greggii (63%), and Zizyphus obtusifolia (64%) had EDCP values comparable to M. sativa hay (64%). Even t hough high levels of lignin and condensed tannins in leaves affected the ED CP, all species tested - A. rigidula and A. berlandieri excepted- may be co nsidered as good available protein supplements for grazing ruminants in nor theastern Mexico and southern Texas, USA.