GC-MS Analysis Sheds Light on Metabolic Risks in Japan’s Native Noma Horses

A team of researchers made up of representatives from several Japanese and Vietnamese universities, animal clinics, and testing services set out to screen for metabolic abnormalities in neonatal foals that died among Noma horses, using laboratory tests, amino acid (AA) and gas chromatography-mass spectrometry (GC-MS) analyses, and pathological examinations. In addition, they investigated the nucleotide sequences of several genes potentially linked to metabolic disorders. A paper based on their findings was published in the Journal of Equine Sciences (1).

Japanese native horses with small body sizes, the reeding of Noma horses began in 1978 with a small number of founders at a public ranch in Imabari City, Ehime, Japan; they were bred as a genetically closed population and totaled less than 100 horses (2).

As a result, there may be a great risk of hereditary disorders caused by inbreeding depression within this group. The prevention of hereditary disorders is important to ensure stable breeding and conservation of the breed (1).

The researchers report that, while a considerable number of foals have been born recently, a significant proportion of them have been lost due to abortion, stillbirth, or neonatal death (1). While there are many potential causes for neonatal death in other breeds of horses, such as premature birth, complications during delivery, infections and septicemia, congenital physical defects, and metabolic disorders (3 –7), the causes of neonatal death in Noma horses remain unknown. While GC-MS has been used in horses for testing of banned substances (8,9), there have been few reports presenting its application in detecting metabolic disorders (10,11).

Thirteen foals were born at the Noma horse ranch (Nomauma Highland Public Ranch, Imabari, Ehime, Japan) between November 2021 and July 2023. Six of these foals were born successfully, one was stillborn, and six died during the neonatal period (1 to 8 days after birth). Of these, the six normal foals and six dead neonatal foals were used in this study. Data analysis revealed high levels of aspartate transaminase, lactate dehydrogenase, creatine kinase and low globulin and glucose levels in the dead foals. The AA and GC-MS analyses also revealed elevated levels of ammonia, orotic acid, and uracil in two of the foals, while citrulline, arginine, and ornithine levels were low or within normal ranges, which suggested accelerated pyrimidine synthesis and suppressed urea cycle activity. One of the foals had high uric acid and tyrosine levels, hypoglycemia, and liver dysfunction; this suggested glycogen storage disease. In another foal, hypertyrosinemia was suggested because of high phenylalanine and tyrosine levels. While the researchers conducted a sequencing analysis of the ornithine transcarbamylase, argininosuccinatelyase, argininosuccinate synthase 1, uridine monophosphate synthase, G6PC1, and G6PT1/SLC37A4 genes associated with metabolic disorders, no mutations were detected (1).

Although metabolic pathways abnormalities resembling certain hereditary metabolic disorders were observed in neonatal foals that died in Noma horses, no specific mutations were identified in candidate genes, making hereditary disorders less likely. While the cause of neonatal death in Noma horses could not be clarified in this study, the researchers believe that determining whether genetic factors contributed to these deaths is essential for future breeding programs aimed at conserving the Noma horse population. More comprehensive genetic analyses, therefore, such as whole genome sequencing using next-generation sequencing, may be required for this purpose (1).

References

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2. Imabari City. The Origin and Transition of Noma Horse. in: The Noma Horse. Imabari City, Ehime, 1994, pp. 1–11. (in Japanese)
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