Division of Animal Science, University of Missouri, Columbia, MO 65211, USA.
J Anim Sci. 2021 Dec 1;99(12). doi: 10.1093/jas/skab349.
This study used 18 calves (295 ± 29 kg) and 18 yearlings (521 ± 29 kg) fed whole, cracked, or steam-flaked corn (SFC) to evaluate nutrient digestion and energy balance across different types of processed corn and sizes of cattle. Cattle were fed a diet comprised of 75% corn (dry matter [DM]-basis) from whole, cracked, or SFC to 2.5-times maintenance energy requirements. Subsequently, cattle were placed in individual stanchions, and urine and feces were collected together with measures of gas production via indirect calorimetry. Data were analyzed using the MIXED procedure of SAS. There was no interaction between corn processing and cattle size (P ≥ 0.40). Time spent ruminating (min/d) and rumination rate (min/kg DM intake [DMI]) were not affected by corn processing or cattle size. The eating rate (min/kg DMI) was faster (P < 0.01) for yearlings compared with calves. Total tract starch digestion was greatest (P = 0.01) for cattle fed SFC (97.5%), intermediate in cattle fed cracked (92.4%), and least in cattle fed whole corn (89.5%). Dietary digestible energy and metabolizable energy (Mcal/kg DMI) were greater (P ≤ 0.05) for cattle fed SFC compared with cracked or whole. A greater proportion of digestible energy was lost to heat production (P = 0.01) in cattle fed whole corn compared with cracked and tended to be greater (P = 0.08) in cattle fed SFC than cracked. Conversion of digestible energy to metabolizable energy in this study was more closely related to a dynamic model used to estimate metabolizable energy of feeds to dairy cows than to a linear model used to predict metabolizable energy of feeds to beef cattle. If library estimates of net energy for maintenance are correct, then retained energy (Mcal/d) should have been similar between each type of processed corn; however, retained energy was greater (P < 0.01) for cattle fed cracked compared with whole corn and tended to be greater (P = 0.06) compared with SFC. Yet, observed amounts of net energy based on measures of retained energy were not different (P ≥ 0.60) between cracked and SFC. Nitrogen balance was not affected (P ≥ 0.30) by corn processing or cattle size, although cattle fed cracked had numerically greater (P ≤ 035) N retention. These data indicate that physical processing of corn provides greater net energy to cattle in comparison to whole corn.
本研究使用了 18 头小牛（295±29 公斤）和 18 头青年牛（521±29 公斤），分别饲喂整粒玉米、破碎玉米或蒸汽压片玉米（SFC），以评估不同加工类型的玉米和不同体型的牛的养分消化和能量平衡。牛饲喂的日粮由 75%的整粒、破碎或 SFC 玉米（干物质[DM]-基础）组成，满足 2.5 倍维持能量需要。随后，将牛单独关在牛栏中，通过间接测热法收集尿液和粪便，并测量气体生成量。数据采用 SAS 的 MIXED 程序进行分析。玉米加工与牛体型之间没有相互作用（P≥0.40）。反刍时间（min/d）和反刍速率（min/kg DM 采食量[DMI]）不受玉米加工或牛体型的影响。青年牛的采食速度（min/kg DMI）比小牛快（P＜0.01）。全肠道淀粉消化率以 SFC 组最高（P=0.01），破碎组次之（P=0.01），整粒组最低（P=0.01）。SFC 组牛的饲粮可消化能和代谢能（Mcal/kg DMI）高于破碎组或整粒组（P≤0.05）。与破碎组和 SFC 组相比，整粒组玉米中更多的可消化能以热能形式损失（P=0.01），且 SFC 组有增加的趋势（P=0.08）。在本研究中，可消化能向代谢能的转化率与用于估计奶牛饲料代谢能的动态模型更相关，而不是用于预测肉牛饲料代谢能的线性模型。如果维持净能的库估计值是正确的，那么每种加工类型的玉米的保留能量（Mcal/d）应该相似；然而，与整粒玉米相比，破碎玉米组牛的保留能量更高（P＜0.01），与 SFC 组相比，这种趋势也更高（P=0.06）。然而，基于保留能量测量的净能实际量在破碎组和 SFC 组之间没有差异（P≥0.60）。氮平衡不受玉米加工或牛体型的影响（P≥0.30），尽管破碎组牛的氮保留量有数值上的增加（P≤0.35）。这些数据表明，与整粒玉米相比，玉米的物理加工为牛提供了更多的净能。
