Residues and contaminants in donkey milk: what has been measured so far

Heavy metals: according to the authors, the EU maximum level for lead in raw milk of 0.02 mg/kg applies to donkey milk. In a study of 45 samples from Sicily, Calabria and Emilia-Romagna, mean lead was 13.88 µg/kg; 11% of samples exceeded the maximum level (20% on one farm, 7% on the other two). In 112 samples from Martina Franca jennies in Reggio Emilia, lead averaged 3.2 µg/kg, and in 17 samples from Turkey it was below the limit of detection; 19.59–48.2 µg/kg lead are reported from Romania.

Aflatoxin M1: the mould toxin was detected in 5 of 9 studies, including a feeding trial with deliberately contaminated maize. The other detections ranged from 0.003 to 0.035 µg/kg; the EU maximum level for raw milk is 0.05 µg/kg. No aflatoxin M1 was found in studies with 84, 90 and 70 samples.

Carry-over from feed: in the only feeding trial, six jennies received maize containing 202 µg aflatoxin B1 and 11 µg B2 over 12 days; carry-over into milk was 0.02%. The authors explain the low values by grazing, low casein content and digestion as non-ruminants.

Pesticides and PCBs: according to the review there are only two papers from Italy (45 and 55 samples). Indicator PCBs and p,p’-DDE were typical; values in the older study were mostly below legal maximum levels, while in the more recent one non-dioxin-like PCBs ranged from 1.26 to 872.00 ng/g fat. Jennies that exclusively grazed had higher values than those receiving mixed feed.

Veterinary drugs: the authors found no published data on antibiotic or antiparasitic residues in donkey milk. In the USA donkeys are classed as a “minor species”, and drug doses are usually derived from horses; ivermectin is not intended for lactating jennies because neither a withdrawal period nor a maximum residue limit has been set.

Prevention: the authors recommend good agricultural, manufacturing and veterinary practice, feed testing, HACCP concepts and specific limits and monitoring programmes for donkey milk.