Group of Research in Ruminants (G2R), Department of Animal and Food Sciences, Universitat Autonoma de Barcelona, Bellaterra, Barcelona, Spain.
Department of Animal Science, Faculty of Agriculture, University Putra Malaysia, Serdang, Selangor, Malaysia.
PLoS One. 2019 Feb 8;14(2):e0202457. doi: 10.1371/journal.pone.0202457. eCollection 2019.
The aim of the study is to identify the candidate biomarkers of heat stress (HS) in the urine of lactating dairy goats through the application of proton Nuclear Magnetic Resonance (1H NMR)-based metabolomic analysis. Dairy does (n = 16) in mid-lactation were submitted to thermal neutral (TN; indoors; 15 to 20°C; 40 to 45% humidity) or HS (climatic chamber; 37°C day, 30°C night; 40% humidity) conditions according to a crossover design (2 periods of 21 days). Thermophysiological traits and lactational performances were recorded and milk composition analyzed during each period. Urine samples were collected at day 15 of each period for 1H NMR spectroscopy analysis. Principal component analysis (PCA) and partial least square-discriminant analysis (PLS-DA) assessment with cross validation were used to identify the goat urinary metabolome from the Human Metabolome Data Base. HS increased rectal temperature (1.2°C), respiratory rate (3.5-fold) and water intake (74%), but decreased feed intake (35%) and body weight (5%) of the lactating does. No differences were detected in milk yield, but HS decreased the milk contents of fat (9%), protein (16%) and lactose (5%). Metabolomics allowed separating TN and HS urinary clusters by PLS-DA. Most discriminating metabolites were hippurate and other phenylalanine (Phe) derivative compounds, which increased in HS vs. TN does. The greater excretion of these gut-derived toxic compounds indicated that HS induced a harmful gastrointestinal microbiota overgrowth, which should have sequestered aromatic amino acids for their metabolism and decreased the synthesis of neurotransmitters and thyroid hormones, with a negative impact on milk yield and composition. In conclusion, HS markedly changed the thermophysiological traits and lactational performances of dairy goats, which were translated into their urinary metabolomic profile through the presence of gut-derived toxic compounds. Hippurate and other Phe-derivative compounds are suggested as urinary biomarkers to detect heat-stressed dairy animals in practice.
本研究旨在通过应用基于质子磁共振（1H NMR）的代谢组学分析，鉴定泌乳奶山羊尿液中热应激（HS）的候选生物标志物。根据交叉设计（2 个 21 天周期），将处于泌乳中期的 16 只奶牛分别置于热中性（TN；室内；15 至 20°C；40 至 45%湿度）或 HS（气候室；白天 37°C，晚上 30°C；40%湿度）条件下。在每个周期中记录热生理特征和泌乳表现，并分析牛奶成分。在每个周期的第 15 天收集尿液样本进行 1H NMR 光谱分析。使用主成分分析（PCA）和偏最小二乘判别分析（PLS-DA）评估结合交叉验证，从人类代谢组数据库中识别山羊尿液代谢组。HS 增加了直肠温度（1.2°C）、呼吸率（3.5 倍）和水摄入量（74%），但减少了泌乳奶牛的采食量（35%）和体重（5%）。产奶量没有差异，但 HS 降低了牛奶中的脂肪（9%）、蛋白质（16%）和乳糖（5%）含量。代谢组学允许通过 PLS-DA 分离 TN 和 HS 尿液簇。最具区分性的代谢物是马尿酸和其他苯丙氨酸（Phe）衍生物化合物，它们在 HS 奶牛中增加。这些肠道来源的有毒化合物的排泄增加表明，HS 导致有害的胃肠道微生物过度生长，这应该会隔离芳香族氨基酸用于其代谢，并减少神经递质和甲状腺激素的合成，对产奶量和成分产生负面影响。总之，HS 显著改变了奶山羊的热生理特征和泌乳表现，这些变化通过肠道来源的有毒化合物在其尿液代谢组谱中得到体现。马尿酸和其他 Phe 衍生物化合物被认为是检测实际热应激奶牛的尿液生物标志物。
