| Using chemical analysis, in vitro two-stage digestion and in vitro gas production and sheep feeding trials, five experiments were conducted to study the effect of botanic factors including crop variety, maturity stage, N fertilizer administration, plant position, on main chemical components and digestibility of crop residues, and to evaluate the response of lamb growth performance to the treatment with chemical combinations.In Expt 1, Com stalks from two varieties of high oil corn (HOC; 647 and 298), two varieties of typical corn (CAU 80 and CAU 3138) and one specific fodder corn (FC) were used as substrates in an in vitro fermentation experiment to examine the effect of corn types on the nutritional value. The result showed that HOC stalks harvested even at 4/4ML stage had 18.8,2.5 and 1.0 folds of water soluble carbohydrates (WSC), starch and crude fat higher (P<0.001) than typical corn stalks. The in vitro digestibility of DM , NDF and ADF, and gas production(48h) were 38.3%, 21.4%, 25.6% and 51.8% higher (P<0.001) for HOC stalks than typical com stalks. In comparison with typical com stalks, HOC stalks decreased the contents of NDF, ADF and lignin by 27.3%, 32.0% and 39.7% (P<0.001). The digestibilities of DM, NDF and ADF were not only much higher for HOC stalks than those of typical com stalks, but also much higher than those of specific fodder cornstalks, indicating that HOC stalks would be regarded as an ideal fodder or ensilage material for feeding ruminant animals.In Expt 2, using corn stalks from variety Nongda 108 as an experimental material, the six sections (leaf blade, leaf sheath, stem bark, stem pith, stem node, ear husk) were compared for their nutritional value. The result showed that there was significantly difference (P<0.05) in the chemical composition, in vitro digestibility and gas production of different sections. The stem nodes and barks had highest content of total carbohydrates (20.7% and 19.3% respectively) and of ether extract (5.8% and 5.2% respectively), while the stem pith had the lowest content of ether extract The content of crude protein was highest in leaf blades (14.9%), and lowest inear husks (6.9%). The contents of ash, Ca and P were all highest in leaf blade (10.5% 1.03% and 0.1% respectively). Although a highest content of NDF was found in ear husks (77.1%), the highest content of ADF and lignin was present in stem barks (52.0% and 14.4% respectively) and the lowest was in ear husks. The ear husks had highest the in vitro digestibilities of dry matter, NDF and ADF, and maximum gas production, followed by leaf blades, stem piths, stem nodes, leaf sheaths and stem bark. It was concluded that the various sections of com stalks are significantly different in the nutritive values, with the rank from highest to lowest being as follows: ear husks > stem piths > leaf blades > leaf sheaths > stem nodes > stem barks.In Exp. 3, using two varieties of high oil com (HOC; HOC 647 and HOC 298), two varieties of typical com (CAU 80 and CAU 3138) and a specific fodder com (FC) as experimental materials, the effects of maturity stage of kernels (1/2,3/4 and 4/4 milk line) on nutrient content and in vitro digestibility of com stalks were investigated. The results showed that as the com kernels matured, HOC stalks had linear increases (L; P<0.01) in the content of WSC, starch, and crude fat, and DMD and NDFD, but had a linear decrease in the content of both NDF, ADF and lignin (L; PO.001). Compared with the kernel maturity stage at 1/2 milk line, the 4/4 milk line maturity increased the content of WSC and starch, and dry matter digestibility by 26.5 folds, 2.4 folds and 22.7% but reduced the content of NDF, ADF and lignin by 24.1,30.6 and 38.4% respectively. With increasing the maturity stage of corn kernels, typical com stalks, however, showed an opposite change in chemical contents and nutrient digestibilitiesin contrast to HOC stalks. The results of this experiment indicated that the high oil com stalks are a good corn stalk source for animal feeing.In Exp. 4, com stalks from Zea mays L, were se...
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