G Osthoff, S Mason, L Schmidt, A Tordiffe, F Deacon
The two study groups had markedly different measured plasma metabolite profiles, with a coherent difference among branched-chain amino-acid-related metabolites. However, species was inseparable from NMR acquisition batch, and the small giraffe group limits biological and pathway-level inference. The concentrations provide exploratory baseline data rather than formal reference intervals.
BACKGROUND: Blood metabolite profiling can provide descriptive information on physiological variation in wildlife, but interpretation is sensitive to sampling design, specimen matrix and analytical batch.
OBJECTIVES: To characterise quantified blood metabolites in apparently healthy giraffes and white rhinoceroses, examine sex-associated differences within each species, and conduct an exploratory matrix-matched interspecies comparison.
METHODS: Proton nuclear magnetic resonance spectra were available for 24 valid giraffe sampling occasions from 19 animals and for 45 white rhinoceroses. Metabolites were quantified jointly from the original spectra. Design-defined comparisons used log₂-transformed concentrations, Welch tests, Benjamini-Hochberg false-discovery correction, effect sizes and permutation, rank-based, leave-one-out and annotation-confidence sensitivity analyses.
RESULTS: No sex-associated metabolite differences were detected among the 2017 Rooipoort giraffe serum samples. Nine metabolites met the primary false-discovery criterion in the rhinoceros sex comparison, although only N-acetylglucosamine showed consistently strong evidence across all sensitivity analyses. In the comparison of six verified giraffe and 45 rhinoceros EDTA-plasma samples, 36 of 50 metabolites differed by the primary analysis; 28 formed a conservative core supported by all statistical tests and all leave-one-giraffe-out analyses. The core remained significant after adjustment for sex. Collection year was completely confounded with serum versus plasma in giraffes and was not tested inferentially.
CONCLUSIONS: The two study groups had markedly different measured plasma metabolite profiles, with a coherent difference among branched-chain amino-acid-related metabolites. However, species was inseparable from NMR acquisition batch, and the small giraffe group limits biological and pathway-level inference. The concentrations provide exploratory baseline data rather than formal reference intervals.