Hypoglycin A absorption in sheep without concurrent clinical or biochemical evidence of disease.

BACKGROUND: Hypoglycin A (HGA) intoxication after ingestion of Acer spp. tree material has never been confirmed in domesticated ruminants despite their similar grazing habitats. OBJECTIVES: To investigate whether sheep have low HGA bioavailability caused by rumen HGA breakdown. ANIMALS: Stomach and rumen fluid samples from 5 adult horses and 5 adult sheep respectively. Residual serum samples from 30 ewes and lambs. METHODS: Experimental and retrospective cohort study. Hypoglycin A concentration was quantified in horse gastric and sheep ruminal samples after in vitro incubation with Acer pseudoplatanus seeds. Serum samples from grazing sheep (n = 20) and nursing lambs (n = 10) obtained before and after their release onto pastures with and without Sycamore seedlings were analyzed for HGA and methylenecyclopropyl-acetic acid carnitine, and serum biochemistry. RESULTS: Neither ovine rumen nor equine gastric fluid affected HGA content in samples incubated for up to 2 hours. Despite HGA's detection in serum from sheep (n = 13/15; median, 23.71 ng/mL; range, 5.62-126.4 ng/mL) grazing contaminated pastures and in their nursing lambs (n = 2/5; median, 12.5 ng/mL; range, 8.82-15.67 ng/mL), there was no apparent clinical or subclinical disease. CONCLUSIONS AND CLINICAL IMPORTANCE: Any reduced sensitivity to HGA intoxication in sheep seems unrelated to ruminal degradation. Serum HGA concentrations in sheep were similar to those of subclinically affected atypical myopathy horses. Any reduced sensitivity of sheep to HGA might be related to greater metabolic resistance rather than selective grazing habits or lower bioavailability. Hypoglycin A was found in nursing lambs, suggesting that HGA is excreted in milk.

Richard Watson.

An inspirational equine veterinary surgeon with a keen interest in racing, to whom horses were a way of life. He took much pride in the success of his homebred racehorses.