Department of Animal Biosciences, University of Guelph, Guelph, ON, Canada.
Evonik Nutrition & Care GmbH, Hanau-Wolfgang, Germany.
J Anim Sci. 2020 May 1;98(5). doi: 10.1093/jas/skaa157.
Thirty five barrows (initial body weight [BW]: 15.1 ± 1.0 kg) were used to determine the effect of partially replacing Gly + Ser with Thr in reduced crude protein (CP) diets on growth performance, protein deposition in carcass and viscera, and skin collagen abundance during the late nursery phase to 25 kg BW. Pigs were individually fed one of five iso-nitrogenous diets (n = 7) for 21 d. The basal diet met estimated essential amino acids (AA) requirements by using all essential AA plus Gly and Ser in free form (CON; 12.1% CP; as-fed, analyzed contents). The remaining four diets were formulated by reducing total Gly and Ser concentrations to 60% or 20% of the CON diet. The N removed with Gly and Ser was replaced with either crystalline Thr or Glu. Total analyzed Thr made up either 1.59% (T1; 12.5% CP) or 2.34% (T2; 12.2% CP) of the Thr-supplemented diets, and total analyzed Glu made up either 3.47% (G1; 12.7% CP) or 4.64% (G2; 12.9% CP) of the Glu-supplemented diets. Pigs were slaughtered on day 21 to determine body composition and skin collagen abundance via bright field microscopy. Overall, average daily gain (ADG) and G:F and final carcass weights were greater for pigs fed diets supplemented with Glu (G1 + G2) vs. those fed diets supplemented with Thr (T1 + T2; P < 0.05, P = 0.060, and P = 0.050 for ADG, G:F, and final carcass weight, respectively); intermediate values were observed for CON. Nitrogen retention in carcass plus viscera and the AA profile of deposited protein in the carcass were not influenced by dietary treatment. Pigs fed the T2 and G2 diets had greater retention of Thr (vs. CON and G2) and Glu (vs. CON and T2) in the viscera protein, respectively (P < 0.05). The apparent utilization efficiency of standardized ileal digestible Thr for protein deposition in carcass plus viscera was less for pigs fed T2 (15.1%) vs. those fed CON (56.7%) or G2 (58.6% ± 2.9%) diets (P < 0.001). Only pigs fed T1 had skin collagen abundance not different from CON; pigs fed G1, G2, and T2 had reduced skin collagen abundance compared with CON and T1 (P < 0.01). Using Glu as an N source when Gly and Ser were reduced to 60% and 20% of CON in reduced CP diets maintained ADG for pigs between 15 and 25 kg BW, whereas supplying Thr as a N source reduced ADG and carcass weight. When dietary Gly and Ser were supplied at 60% of CON, only Thr supplementation rescued skin collagen abundance. Therefore, supplemental Thr at excess levels is not sufficient to replace N from Gly and Ser in reduced CP diets fed to late nursery pigs, despite supporting skin collagen abundance as a secondary indicator of Gly status.
35 头去势公猪（初始体重 [BW]：15.1±1.0kg）用于确定在生长后期（25kg BW）用减少粗蛋白（CP）饲粮中甘氨酸（Gly）和丝氨酸（Ser）部分替代苏氨酸（Thr）对生长性能、胴体和内脏器官蛋白质沉积以及皮肤胶原蛋白丰度的影响。猪单独饲喂 5 种等氮饲粮中的 1 种（n=7）21d。基础饲粮采用游离形式的所有必需氨基酸（AA）加上 Gly 和 Ser 来满足估计的必需氨基酸（AA）需要量（CON；12.1%CP；实测，分析含量）。剩余的 4 种饲粮通过将 Gly 和 Ser 的总浓度降低到 CON 饲粮的 60%或 20%来配制。用 Gly 和 Ser 去除的氮用结晶 Th 或 Glu 替代。补充 Th 的饲粮中总分析性 Thr 分别占 1.59%（T1；12.5%CP）或 2.34%（T2；12.2%CP），补充 Glu 的饲粮中总分析性 Glu 分别占 3.47%（G1；12.7%CP）或 4.64%（G2；12.9%CP）。第 21 天屠宰猪，通过明场显微镜测定体组成和皮肤胶原蛋白丰度。总体而言，与饲喂添加 Thr 饲粮（T1+T2）的猪相比，饲喂添加 Glu 饲粮（G1+G2）的猪的平均日增重（ADG）和饲料效率以及终体重更高（P<0.05，ADG、饲料效率和终体重的 P 值分别为 0.060 和 0.050）；CON 饲粮的中间值。氮在胴体加内脏器官中的保留和沉积在胴体中的蛋白质的 AA 谱不受饲粮处理的影响。与 CON 和 G2 饲粮相比，饲喂 T2 和 G2 饲粮的猪在内脏器官蛋白质中保留了更多的 Thr（P<0.05）和 Glu（P<0.05）。饲喂 T2 饲粮的猪（15.1%）用于沉积胴体加内脏器官蛋白质的标准化回肠可消化 Thr 的表观利用率低于 CON（56.7%）或 G2（58.6%±2.9%）饲粮（P<0.001）。仅饲喂 T1 的猪的皮肤胶原蛋白丰度与 CON 无差异；与 CON 和 T1 相比，饲喂 G1、G2 和 T2 的猪的皮肤胶原蛋白丰度降低（P<0.01）。当将 Gly 和 Ser 减少到 CON 的 60%和 20%时，用 Glu 作为氮源可以维持 15-25kg BW 猪的 ADG，而用 Thr 作为氮源则降低 ADG 和胴体重。当饲粮 Gly 和 Ser 供应为 CON 的 60%时，只有 Thr 补充剂才能挽救皮肤胶原蛋白丰度。因此，尽管补充 Thr 作为 Gly 状态的次要指标支持皮肤胶原蛋白丰度，但补充过量的 Thr 不足以替代减少 CP 饲粮中 Gly 和 Ser 的氮。
