Bartlett K S, McKeith F K, VandeHaar M J, Dahl G E, Drackley J K
Department of Animal Sciences, University of Illinois, Urbana, 61801, USA.
J Anim Sci. 2006 Jun;84(6):1454-67. doi: 10.2527/2006.8461454x.
Previous research has demonstrated that increasing the CP concentration from 16 to 26% in milk replacers fed to male preruminant dairy calves at 1.5% of BW (DM basis) daily resulted in increased ADG, G:F, and deposition of lean tissue. However, the effects of dietary CP would be expected to vary depending on ME intake. Here, male Holstein calves < 1 wk old were used to determine the effects of feeding rate and CP concentration of isocaloric, whey protein-based milk replacers on growth and body composition. After a 2-wk standardization period, calves were assigned randomly to an initial baseline group or to treatments in a 2 x 4 factorial arrangement of feeding rate (1.25 or 1.75% of BW daily, DM basis) and milk replacer CP concentration (14, 18, 22, or 26% of DM). No starter was offered, but calves had free access to water. After a 5-wk feeding period, calves were slaughtered and body composition was determined. Increasing the feeding rate increased (P < 0.05) ADG, G:F, empty-body gains of chemical components and energy, the percentage of fat in empty BW gain and in the final empty body, and concentrations of IGF-I and insulin in plasma. Increasing the feeding rate decreased (P < 0.01) percentages of water and protein in the empty body and decreased urea N in plasma. Increasing dietary CP concentration linearly increased (P < 0.05) ADG, body length, heart girth, and gains of water and protein but linearly decreased (P < 0.05) fat gain. As dietary CP increased, fat content in empty body gain decreased, and water and protein increased. Increasing CP concentration increased (quadratic, P < 0.02) G:F, with greatest efficiencies for calves fed 22% CP. Gross energetic efficiency (retained energy:intake energy) was greater (P < 0.05) for calves fed at 1.75% of BW daily. Efficiency of dietary protein use for protein gain was greater for calves fed at 1.75% of BW daily but was not affected by dietary CP. The ratio of protein gain to apparently digestible protein intake above maintenance decreased as dietary CP increased. Interactions (P < 0.05) of feeding rate and CP concentration for gains of water and protein indicated that when dietary CP was 26% the ME supply limited protein use by calves fed at 1.25% of BW daily. Body composition of preruminant calves can be markedly altered by manipulating the protein to energy ratio in milk replacers. These dietary effects on body composition and growth are not predicted by current NRC standards.
先前的研究表明，给雄性反刍前奶牛犊牛每日按体重（干物质基础）的1.5%饲喂代乳料时，将其中粗蛋白（CP）浓度从16%提高到26%，可使平均日增重（ADG）、生长肥育比（G:F）和瘦肉组织沉积增加。然而，日粮粗蛋白的影响预计会因代谢能（ME）摄入量的不同而有所变化。在此，选用1周龄以下的雄性荷斯坦犊牛来确定等热量、基于乳清蛋白的代乳料的饲喂量和粗蛋白浓度对生长及身体组成的影响。经过2周的标准化期后，犊牛被随机分配到初始基线组或采用2×4析因设计的处理组，处理因素为饲喂量（每日按体重的1.25%或1.75%，干物质基础）和代乳料粗蛋白浓度（干物质的14%、18%、22%或26%）。不提供开食料，但犊牛可自由饮水。经过5周的饲喂期后，宰杀犊牛并测定身体组成。提高饲喂量可使ADG、G:F、化学成分和能量的空腹体重增加、空腹体重增加和最终空腹体重中脂肪的百分比以及血浆中胰岛素样生长因子-I（IGF-I）和胰岛素浓度增加（P<0.05）。提高饲喂量可使空腹体重中水和蛋白质的百分比降低（P<0.01），并使血浆中尿素氮降低。日粮粗蛋白浓度的增加使ADG、体长、胸围以及水和蛋白质的增加呈线性增加（P<0.05），但脂肪增加呈线性降低（P<0.05）。随着日粮粗蛋白的增加，空腹体重增加中的脂肪含量降低，水和蛋白质增加。粗蛋白浓度的增加使G:F增加（二次效应，P<0.02），对于饲喂22%粗蛋白的犊牛效率最高。每日按体重1.75%饲喂的犊牛总能效率（留存能量:摄入能量）更高（P<0.05）。每日按体重1.75%饲喂的犊牛用于蛋白质增加的日粮蛋白质利用效率更高，但不受日粮粗蛋白的影响。随着日粮粗蛋白的增加，蛋白质增加与维持以上表观可消化蛋白质摄入量的比值降低。水和蛋白质增加量的饲喂量和粗蛋白浓度之间存在交互作用（P<0.05），这表明当日粮粗蛋白为26%时，每日按体重1.25%饲喂的犊牛的代谢能供应限制了蛋白质的利用。通过控制代乳料中的蛋白质能量比，可显著改变反刍前犊牛的身体组成。目前的美国国家研究委员会（NRC）标准无法预测这些日粮对身体组成和生长的影响。
