Mastellar S L, Coleman R J, Urschel K L
Department of Animal and Food Sciences, University of Kentucky, Lexington, KY 40546, USA.
Department of Animal and Food Sciences, University of Kentucky, Lexington, KY 40546, USA.
Vet J. 2016 Oct;216:93-100. doi: 10.1016/j.tvjl.2016.07.007. Epub 2016 Jul 19.
Lysine has been reported as the first limiting amino acid in typical equine diets. Indicator amino acid oxidation (IAAO) has become the standard method for determining amino acid requirements in other species, but prior to this study, it has not been used to determine equine requirements. The aim of this study was to evaluate whole body protein synthesis and plasma and muscle amino acid concentrations in response to graded levels of lysine intake in yearling horses. Six Thoroughbred colts (358 ± 5 kg) were fed each of six treatment lysine intakes ranging from 76 to 136 mg/kg body weight/day. Blood samples were taken before and 90 min after the morning concentrate meal. Gluteal muscle biopsies were taken ~100 min after the morning concentrate meal. The next day, whole body phenylalanine kinetics were determined using a 2 h primed, constant infusion of [(13)C] sodium bicarbonate followed by a 6 h primed, constant infusion of [1-(13)C] phenylalanine. Plasma lysine concentrations increased linearly (P <0.05) at both the 0 and 90 min time points with increasing lysine intakes. Free muscle asparagine, aspartate, arginine, glutamine, lysine, taurine and tryptophan concentrations responded quadratically to lysine intake (P <0.05). Phenylalanine kinetics did not differ between treatment intakes (P > 0.10). A broken line analysis of lysine intake and phenylalanine oxidation failed to yield a breakpoint from which to determine a lysine requirement. These diets may have been limiting in an amino acid other than lysine, underscoring the lack of data concerning amino acid requirements and bioavailability data in the horse.
赖氨酸被报道为典型马日粮中的第一限制性氨基酸。指示剂氨基酸氧化法（IAAO）已成为确定其他物种氨基酸需求量的标准方法，但在本研究之前，尚未用于确定马的氨基酸需求量。本研究的目的是评估一岁马在不同赖氨酸摄入量水平下的全身蛋白质合成以及血浆和肌肉氨基酸浓度。六匹纯种马驹（358±5千克）分别饲喂六种赖氨酸摄入量不同的日粮，摄入量范围为76至136毫克/千克体重/天。在早晨精料饲喂前和饲喂后90分钟采集血样。在早晨精料饲喂后约100分钟采集臀肌活检样本。第二天，通过先静脉注射2小时的[(13)C]碳酸氢钠，随后再静脉注射6小时的[1-(13)C]苯丙氨酸来测定全身苯丙氨酸动力学。随着赖氨酸摄入量增加，在0和90分钟时间点血浆赖氨酸浓度均呈线性增加（P<0.05）。肌肉中的游离天冬酰胺、天冬氨酸、精氨酸、谷氨酰胺、赖氨酸、牛磺酸和色氨酸浓度对赖氨酸摄入量呈二次反应（P<0.05）。不同处理组的苯丙氨酸动力学无差异（P>0.10）。对赖氨酸摄入量和苯丙氨酸氧化进行折线分析未能得出确定赖氨酸需求量的转折点。这些日粮可能在除赖氨酸以外的其他氨基酸方面存在限制，这凸显了马的氨基酸需求量和生物利用度数据的匮乏。
