Variation in nutrition is a key determinant of growth, body composition, and the ability of animals to perform to their genetic potential. Depending on the quality of feed available, animals may be able to overcome negative effects of prior nutritional restriction, increasing intake and rates of tissue gain, but full compensation may not occur. A 2 x 3 x 4 factorial serial slaughter study was conducted to examine the effects of prior nutritional restriction, dietary energy density, and supplemental rumen undegradable protein (RUP) on intake, growth and body composition of lambs. After an initial slaughter (n=8), 124 4-month old Merino cross wethers (28.4±1.8 kg) were assigned to either restricted (LO, 500 g/d) or unrestricted (HI,1500 g/d) intake of lucerne & oat pellets. After 8 weeks, 8 lambs/group were slaughtered and tissue weights and chemical composition were measured. Remaining lambs were randomly assigned to a factorial combination of dietary energy density (7.8, 9.2, & 10.7 MJ/kg DM) and supplemental RUP (0, 30, 60, 90 g/d) and fed ad libitum for a 12 to 13-week experimental period before slaughter and analysis. By week 3 of the experimental period, lambs fed the same level of energy had similar DMI (g/d) and MEI (MJ/d) (P>0.05), regardless of prior level of nutrition. Restricted-refed (LO) lambs had higher rates of fat and protein gain than HI lambs (P<0.05) but had similar visceral masses (P>0.05). However, LO lambs were lighter and leaner at slaughter, with proportionally larger rumens and livers (P<0.05). Tissue masses increased with increasing dietary energy density, as did DMI, energy and nitrogen (N) retention (% intake), and rates of protein and fat gain (P<0.05). The liver increased proportionally with increasing dietary energy density and RUP (P<0.05), but rumen size decreased relative to the empty body as dietary energy density increased (P<0.05) and did not respond to RUP (P>0.05). Fat deposition was greatest in lambs fed 60g/d supplemental RUP (P<0.05). However, lambs fed 90 g/d were as lean as lambs that did not receive supplement (P0, P>0.05), with poorer nitrogen retention and proportionally heavier livers than P0 lambs (P<0.05). In general, visceral protein was the first tissue to respond to increased intake during refeeding, followed by non-visceral protein and fat, highlighting the influence of differences in tissue response over time on animal performance and body composition.

中文翻译：

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日粮能量密度和补充瘤胃不可降解蛋白对营养限制恢复羔羊采食量、内脏和胴体组成的影响

营养的变化是动物生长、身体成分和动物发挥其遗传潜力的能力的关键决定因素。根据可用饲料的质量，动物可能能够克服先前营养限制、增加采食量和组织获得率的负面影响，但可能不会发生完全补偿。进行了一项 2 x 3 x 4 因子连续屠宰研究，以检查先前的营养限制、日粮能量密度和补充瘤胃不可降解蛋白 (RUP) 对羔羊采食量、生长和身体成分的影响。在首次屠宰后 (n=8)，124 只 4 个月大的美利奴杂交种 (28.4±1.8 kg) 被分配到限制（LO，500 g/d）或不限制（HI，1500 g/d）摄入量的卢塞恩& 燕麦颗粒。8周后，屠宰8只羔羊/组并测量组织重量和化学成分。剩余的羔羊被随机分配到日粮能量密度（7.8、9.2 和 10.7 MJ/kg DM）和补充 RUP（0、30、60、90 g/d）的因子组合中，并随意喂食 12 至 13-屠宰前一周的实验期和分析。到实验期的第 3 周，饲喂相同能量水平的羔羊具有相似的 DMI (g/d) 和 MEI (MJ/d) (P>0.05)，无论之前的营养水平如何。限制饲喂 (LO) 羔羊的脂肪和蛋白质增加率高于 HI 羔羊 (P<0.05)，但内脏质量相似 (P>0.05)。然而，LO 羔羊在屠宰时更轻、更瘦，瘤胃和肝脏比例较大（P<0.05）。组织质量随着膳食能量密度的增加而增加，DMI 也是如此，能量和氮（N）保留（摄入百分比），以及蛋白质和脂肪增加率（P<0.05）。肝脏随着日粮能量密度和 RUP 的增加成比例地增加 (P<0.05)，但随着日粮能量密度的增加 (P<0.05) 和对 RUP 没有反应 (P>0.05)，相对于空腹的瘤胃大小减小。饲喂 60g/d 补充 RUP 的羔羊脂肪沉积量最大 (P<0.05)。然而，饲喂 90 g/d 的羔羊与未接受补充的羔羊一样瘦（P0，P>0.05），与 P0 羔羊相比，氮保留较差，肝脏比例较重（P<0.05）。一般来说，内脏蛋白质是第一个对再喂食期间摄入增加做出反应的组织，其次是非内脏蛋白质和脂肪，