I recently came across a case report of cattle being poisoned by apricot kernels, a reminder of the fact that the seeds (and sometimes leaves) from fruits such as apricots, peaches, and other members of the Prunus genus contain glycosides such as amygdalin that can release the deadly gas hydrogen cyanide. This fact is well known to entomologists who will use a few torn leaves from a cherry tree, in a jar, to kill the specimens that they collect.
The case, reported this week in the Veterinary Record, describes how a farmer in Switzerland obtained a large quantity of soft hulls, separated from the inner part of the apricot kernels. (The report does not link the use of this exotic feedstuff to the rise in world feed and grain prices – a worthy subject of another blog?). The apricot kernels were used for the production of traditional gingerbread cake, and the feedstuff was obtained from a local baker in the Appenzelle region. The farmer did not appear to notice the characteristic smell of bitter almonds in the feed, even though the cows did. They were not keen on the new feed, and showed ‘a strong aversion’ to it. The farmer needed to make it much more acceptable by adding silage to increase the palatability. The result of this misadventure was that 5 of the 12 cows fed the apricot hulls showed quite severe symptoms including tremor, salivation, opisthotonus, tympany, and dyspnoea, and two of them died. The 3 surviving cows refused to feed for another 24 hours, and had reduced milk production, but they recovered without treatment.
The apricot hulls and kernels were found to contain a mean hydrogen cyanide (HCN) level of 110 mg/kg, and an amygdalin content which was the equivalent of another 300 mg/kg of HCN. This meant that the 2 kg of the feed given to the each of the cows would have contained at least 820 mg of HCN equivalents, which is close to the reported lethal dose of 2 mg/kg.
Cyanide poisoning is difficult to diagnose. The volatility and rapid breakdown of HCN, often means that samples from suspected poisonings are negative when tested. This is one of the reasons that cyanide is often the poison of choice in crime novels: easy to disguise in any almond flavoured dish, quick, lethal, and hard to detect. In looking for a better way to detect cyanide poisoning the authors of the case report took blood samples to detect thiocyanate. The blood levels in the three affected cows were 145, 209, and 211 μmol/L compared to normal levels of 50-60 μmol/L. This showed that high serum thiocyanate can be an indicator of cyanide poisoning, although there are other factors that can increase thiocyanate in blood, and these need also to be considered.
Looking into the CAB Abstracts Database for other cases of cyanide poisoning reveals over 30 references. Many of the cases are of goats, whose catholic tastes tempt them to eat leaves of cherry trees if they have access. There are also cases of people being poisoned by apricot kernels by accident (when the kernels were used in making sweets), and in what appears to be attempted suicide.
So, remember, if the feed you are being offered has a distinct smell of bitter almonds then, beware.