Hypoglycin A absorption in sheep without concurrent clinical or biochemical evidence of disease.
Authors: González-Medina Sonia, Bevin William, Alzola-Domingo Rafael, Chang Yu-Mei, Piercy Richard J
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary This investigation challenged the assumption that domestic ruminants are naturally protected from sycamore poisoning (Acer pseudoplatanus toxicity) by examining whether ruminal breakdown of hypoglycin A (HGA) might account for the apparent species difference in susceptibility. Researchers incubated sycamore seeds with rumen and gastric fluids from sheep and horses respectively, then analysed serum samples from grazing ewes, lambs and nursing offspring before and after exposure to contaminated pastures, alongside biochemical markers and clinical monitoring. Despite detecting HGA in the blood of 13 out of 15 sheep grazing on affected pastures (median 23.71 ng/mL) and in 2 out of 5 nursing lambs, none of the animals developed clinical or biochemical evidence of disease, whilst ruminal incubation had no degradative effect on HGA over a 2-hour period. The findings suggest that sheep possess metabolic resilience to HGA rather than protection through bioavailability barriers, and raise an important flag for practitioners: HGA excretion in maternal milk represents a previously unrecognised exposure route for young stock. Rather than assuming sheep are simply resistant to sycamore toxicity, equine and ruminant professionals should recognise that occasional exposure to low HGA concentrations may occur without immediate clinical consequence, whilst the mechanisms underlying true species resistance remain incompletely understood.
Read the full abstract on PubMed
Practical Takeaways
- •Sheep appear to have greater metabolic resistance to hypoglycin A toxicity than horses despite similar serum concentrations, suggesting Sycamore contamination poses lower risk to sheep in mixed grazing situations
- •Detection of HGA in nursing lambs indicates lactational transfer of the toxin; monitor lamb health when ewes graze Acer-contaminated pastures
- •Rumen fermentation does not appear to protect sheep from HGA absorption, so pasture management rather than ruminal metabolism explains differential species susceptibility to atypical myopathy
Key Findings
- •Neither ovine rumen nor equine gastric fluid degraded hypoglycin A during 2-hour in vitro incubation, suggesting rumen breakdown is not responsible for lower sheep susceptibility
- •Serum HGA was detected in 13/15 sheep (median 23.71 ng/mL) and 2/5 nursing lambs (median 12.5 ng/mL) grazing contaminated pastures with no clinical or biochemical evidence of disease
- •Sheep serum HGA concentrations were similar to those of subclinically affected atypical myopathy horses, indicating species differences in metabolic sensitivity rather than bioavailability
- •Hypoglycin A was detected in nursing lamb serum, providing evidence that HGA is excreted in maternal milk