Krehbiel C R, Cranston J J, McCurdy M P
Department of Animal Science, Oklahoma Agricultural Experiment Station, Oklahoma State University, Stillwater, 74078, USA.
J Anim Sci. 2006 Apr;84 Suppl:E34-49. doi: 10.2527/2006.8413_supple34x.
This review assessed the relationships between dietary energy density and animal performance in an effort to evaluate a possible upper limit for energy density in finishing diets for cattle. Data were combined from 49 experiments (69 trials; 243 treatment observations) in which the dietary ME concentration (Mcal/kg of DM) was varied by level of concentrate, grain source, grain processing, and level of supplemental fat. Dietary concentrations of ME were determined using 1) NRC values of ME from diet ingredients; or 2) values derived from the literature, in which ingredient ME had been calculated from animal performance. Procedures for pooling data from multiple studies were used. The dependent variable was fit to a model that included a random slope and intercept clustered by trial. Trial-adjusted dependent variables (animal performance and carcass characteristics) were regressed on the independent variable (dietary ME concentration). Models were fit to cubic equations, and then reduced from cubic to quadratic to linear equations when the cubic and quadratic terms were not significant at P > 0.10. When NRC values were used, the relationship of DMI (% of BW) to dietary ME was linear (DMI decreased as ME increased; R2 = 0.631). However, the slope of ME intake (Mcal/kg of BW(0.75)) vs. dietary ME content did not differ (P > 0.25) from zero, supporting the concept that ruminants on high-grain diets (2.7 to 3.3 Mcal of ME/kg of DM) eat to maintain constant energy intake. Quadratic relationships were observed (P < 0.05) when ADG and G:F vs. dietary ME concentration were analyzed. Gain:feed was maximized with 3.46 (NRC) to 3.65 (calculated) Mcal/kg of ME from the total diet, 2.99 (NRC) to 3.40 (calculated) Mcal/kg of ME from grain, and 0.43 (NRC) to 0.53 (calculated) Mcal/kg of ME from supplemental fat. Most relationships of carcass traits to dietary ME were not significant (P > 0.10). Increased 12th-rib fat at greater ME and increasing KPH suggests greater fat deposition with increasing caloric density. Assuming that NRC ME values for ingredients commonly used in finishing diets are correct, the upper caloric limit for maximizing ADG and G:F was 3.16 and 3.45 Mcal/kg of DM, respectively. Reaching the upper caloric limit for G:F would require most grains to be processed or fed in high-moisture form. Whether maximizing G:F results in the most desirable carcass composition and yield of retail cuts should be determined.
本综述评估了日粮能量密度与动物生产性能之间的关系，旨在评估肉牛育肥日粮能量密度的可能上限。数据来自49项试验（69个试验组；243个处理观测值），其中日粮代谢能（ME）浓度（Mcal/kg干物质）通过精料水平、谷物来源、谷物加工和补充脂肪水平进行变化。日粮ME浓度的测定采用以下两种方法：1）日粮成分的NRC代谢能值；或2）从文献中得出的值，其中成分ME已根据动物生产性能计算得出。采用了合并多项研究数据的方法。将因变量拟合到一个模型中，该模型包括按试验聚类的随机斜率和截距。将试验调整后的因变量（动物生产性能和胴体特性）对自变量（日粮ME浓度）进行回归分析。模型拟合三次方程，当三次项和二次项在P>0.10时不显著时，则从三次方程简化为二次方程再到线性方程。当使用NRC值时，干物质采食量（占体重的百分比）与日粮ME的关系呈线性（随着ME增加，干物质采食量降低；R2 = 0.631）。然而，ME摄入量（Mcal/kg体重0.75）与日粮ME含量的斜率与零无差异（P>0.25），这支持了高谷物日粮（2.7至3.3 Mcal ME/kg干物质）的反刍动物通过采食来维持恒定能量摄入的概念。在分析平均日增重和料重比与日粮ME浓度的关系时，观察到了二次关系（P<0.05）。当全日粮ME为3.46（NRC）至3.65（计算值）Mcal/kg、谷物ME为2.99（NRC）至3.40（计算值）Mcal/kg以及补充脂肪ME为0.43（NRC）至0.53（计算值）Mcal/kg时，料重比达到最大值。胴体性状与日粮ME的大多数关系不显著（P>0.10）。随着ME增加，第12肋脂肪增加，肾脏、盆腔和心脏脂肪（KPH）增加，这表明随着热量密度增加，脂肪沉积增加。假设育肥日粮中常用成分的NRC ME值正确，使平均日增重和料重比最大化的热量上限分别为3.16和3.45 Mcal/kg干物质。要达到料重比的热量上限，大多数谷物需要进行加工或以高水分形式饲喂。是否使料重比最大化会导致最理想的胴体组成和零售切块产量，这一点有待确定。
