本试验旨在探讨在饲粮中应用玉米替代象草，增加能量水平对肉牛生长、消化及血清生化指标的影响，从而为肉牛育肥过程中合理使用能量饲料提供依据。选取30头21月龄左右的杂交公牛[（449.4±45.7）kg]，随机分为3组，分别为低能组、中能组和高能组，对应饲粮干物质中玉米和象草的含量分别为12.5%、22.5%、32.5%和60.0%、50.0%、40.0%，每组10头。试验期45 d，其中预试期5 d，正试期40 d。正试期内测定平均日增重、料重比，并计算经济效益；最后5 d用全收粪法测定干物质表观消化率；最后2 d分别于晨饲前及晨饲后2.5、6.0 h测定瘤胃液pH；最后1 d采集血液用于测定血清生化指标。结果表明：1）平均日增重以高能组最高（1.31 kg/d），中能组次之（1.21 kg/d），低能组最低（0.96 kg/d），但各组差异不显著（P>0.05）；各组干物质采食量、干物质表观消化率均为高能组 > 中能组 > 低能组，高能组与低能组差异显著（P<0.05），而料重比则反之；2）晨饲前瘤胃液pH以高能组最低，但各组间差异不显著（P>0.05）；高能组、中能组晨饲后2.5和6.0 h瘤胃液pH显著低于低能组（P<0.05）；3）经济效益以低能组最低，低能组毛盈利分别比高能组和中能组低46.10%和40.28%；4）各组血清生化指标差异均不显著（P>0.05）。综合得出，肉牛育肥期以象草为唯一粗饲料时，提高饲粮中玉米含量以增加能量水平提高了肉牛干物质采食量、干物质表观消化率、平均日增重和经济效益，降低了料重比；当饲粮中玉米含量达32.5%时对瘤胃发酵和肉牛健康也无不利影响，具有最大的养殖经济收益。

This study was conducted to research the influences of increasing dietary energy level by replacing elephant grass with corn on growth, digestion and serum biochemical parameters of beef cattle, aimed to provide a theoretical basis for optimum supplement of energy for beef cattle fattening. Thirty healthy crossbred beef cattle at 21 months of age with body weight of (449.4±45.7) kg were randomly allocated into 3 groups with 10 heads per group. The three groups were low energy (LE) group, medium energy (ME) group and high energy (HE) group, and the corresponding contents of corn and elephant grass in dietary dry matter were 12.5%, 22.5%, 32.5% and 60.0%, 50.0%, 40.0%, respectively. The experimental period lasted for 45 days including 5-day pre-trail period and 40-day trial period. Average daily gain (ADG), feed to gain ratio (F/G) and economic benefit were calculated during the trial period; dry matter apparent digestibility was measured by total fecal collection method at the last 5 days; rumen fluid pH of was measured before morning feeding and at 2.5 and 6.0 h after morning feeding at the last 2 days; blood sample was collected to measure serum biochemical parameters at the last day. The results showed as follows:1) ADG was the highest in HE group (1.31 kg/d) and the lowest in LE group (0.96 kg/d), and that in ME group was in the middle (1.21 kg/d), while there was no significant difference among groups (P>0.05); dry matter intake and dry matter apparent digestibility showed HE group > ME group > LE group, and the differences between HE group and LE group were significant, while F/G showed the opposite change; 2) rumen fluid pH before morning feeding in HE group was the lowest, but the difference among groups was not significant (P>0.05); rumen fluid pH at 2.5 and 6.0 after morning feeding in HE group and ME group was significantly lower than in LE group (P<0.05); 3) economy benefit in LE group was the lowest among three groups, and gross profit was lower than HE group and ME group by 46.10% and 40.28%, respectively; 4) there were no significant differences of serum biochemical parameters among three groups (P>0.05). In conclusion, when elephant grass is used as the only forage in beef cattle fattening, dry matter intake, dry matter apparent digestibility, average daily gain and economic benefit are improved while F/G is reduced when increasing energy level by replacing elephant grass with corn; there are no adverse effects on rumen fermentation and animal health even though corn occupies 32.5% of diet, and the best economic benefit is obtained.