We executed two studies to investigate the possibility of reducing crude protein (CP) content throughout feedlot of growing lambs, when they are changing their body composition, and passing from most protein retention to fat deposition for finishing. A performance trial (EXP 1) with 40 Santa Ines crossbred sheep (initial body weight (BW) of 15.6±1.6 kg) were carried out in a completely randomized design, with four treatments and 10 repetitions. The EXP 1 lasted a total of 85 days, with 15 for adaptation and 70 for data collection. The investigated diets were formulated with two CP contents, in which 150 g of CP/kg DM (High CP (HCP)) diets represented the adequate nutritional requirement for growing lambs, or 130 g of CP/kg DM (Low CP (LCP diets)), which represented the reduced content. We also evaluated the feedlot phases, in which the initial phase-feeding (IPF) comprised day 1 to 35, and the final phase-feeding (FPF) comprised day 36 to 70. The combination of these factors resulted in the following treatments (T): T1 - Animals fed with the lower CP content during all the feedlot period, 130 in IPF and 130 g of CP/kg DM in FPF (T1: LCP-LCP); T2-Animals were fed with increasing content of CP along feedlot (T2: LCP-HCP); T3- Animals were fed with decreasing content of CP during the phases (T3: HCP-LCP); T4 - Animals were fed with the greater CP content during all feedlot period (T4: HCP-HCP). We carried out a second study to investigate the ruminal fermentation parameters (EXP 2). Four adult Santa Ines sheep (average BW of 60.6±10.6 kg), fistulated in rumen, were distributed in four 2 × 2 Latin squares. The same CP contents from EXP 1 were evaluated: LCP diets (130 g of CP/kg DM) and HCP diets (150 g of CP/kg DM). There was effect (P> 0.05) of CP contents in FPF on CP intake and urinary N excretion, being higher for the animals fed with HCP diets. The phase-feeding did not affect the microbial CP synthesis and microbial efficiency (P> 0.05), and also did not affect (P > 0.05) meat quality. The animals fed with LCP or HCP diets in both IPF and FPF presented a similar ADG (P = 0.65 and P > 0.15, respectively) and final BW (FBW, P = 0.66 and P= 0.24, respectively). Sheep fed with HCP diets had higher concentrations of ruminal ammoniacal N (N-NH₃, P < 0.01), but demonstrated similar (P > 0.05) volatile fatty acids (VFA) production. Our results demonstrate that no benefits on rumen fermentation, performance and meat quality were found when more than LCP diets was provided during the feedlot, nor when phase-feeding was applied to crossbred Santa Ines lambs.

我们进行了两项研究，以调查当生长中的羔羊改变其身体组成并从大多数蛋白质保留到脂肪沉积以完成肥育时，降低整个饲养场粗蛋白质（CP）含量的可能性。用完全随机设计进行了40头Santa Ines杂交绵羊（初始体重（BW）为15.6±1.6千克）的性能试验（试验1），进行了4次治疗和10次重复。EXP 1总共持续85天，其中15天用于适应，70天用于数据收集。所研究的日粮具有两种CP含量，其中150 g CP / kg DM（高CP（HCP））膳食代表了成长羔羊的足够营养需求，或130 g CP / kg DM（低CP（LCP日粮） ）），代表减少的内容。我们还评估了育肥阶段 其中初始阶段喂养（IPF）包含第1至35天，最终阶段喂养（FPF）包含第36至70天。这些因素的结合导致了以下治疗（T）：T1-在整个育肥期中较低的CP含量，IPF为130，FPF为130 g CP / kg DM（T1：LCP-LCP）；向T2-动物饲喂沿着育肥场增加的CP含量（T2：LCP-HCP）；T3-在阶段期间以降低的CP含量喂养动物（T3：HCP-LCP）；T4-在所有饲养场期间以较高的CP含量喂养动物（T4：HCP-HCP）。我们进行了第二项研究，以研究瘤胃发酵参数（EXP 2）。将四只成年瘤胃的成年圣伊内斯成年绵羊（平均体重为60.6±10.6千克）分布在四个2×2拉丁方格中。对来自EXP 1的相同CP含量进行了评估：LCP日粮（130 g CP / kg DM）和HCP日粮（150 g CP / kg DM）。FPF中的CP含量对CP摄入量和尿N排泄有影响（P> 0.05），对于饲喂HCP饮食的动物则更高。分期饲喂不影响微生物CP的合成和微生物效率（P> 0.05），也没有影响肉质（P> 0.05）。用IPF和FPF饲喂LCP或HCP饲料的动物表现出相似的ADG（分别为P = 0.65和P> 0.15）和最终体重（分别为FBW，P = 0.66和P = 0.24）。饲喂HCP日粮的绵羊的瘤胃氨氮（N-NH 分期饲喂不影响微生物CP的合成和微生物效率（P> 0.05），也没有影响肉质（P> 0.05）。用IPF和FPF饲喂LCP或HCP饲料的动物表现出相似的ADG（分别为P = 0.65和P> 0.15）和最终体重（分别为FBW，P = 0.66和P = 0.24）。饲喂HCP日粮的绵羊的瘤胃氨氮（N-NH 分期饲喂不影响微生物CP的合成和微生物效率（P> 0.05），也没有影响肉质（P> 0.05）。用IPF和FPF饲喂LCP或HCP饲料的动物表现出相似的ADG（分别为P = 0.65和P> 0.15）和最终体重（分别为FBW，P = 0.66和P = 0.24）。饲喂HCP日粮的绵羊的瘤胃氨氮（N-NH₃，P <0.01），但显示出相似的（P> 0.05）挥发性脂肪酸（VFA）产生。我们的结果表明，在饲养场中提供超过LCP的日粮，或者对杂交的Santa Ines羔羊进行分期饲喂时，对瘤胃发酵，性能和肉质没有任何益处。