Nematode © Christian SLAGMULDER

Anti-parasitic drugs: humans and animals united in the same fight

Ensuring the safety of food products  

Research carried out at INRA in the 1990s has shown a prolonged presence of ivermectin residue in milk, until about 60 days after treating milking cows.

By Pascale Mollier and Delphine Achour, translated by Inge Laino
Updated on 06/20/2017
Published on 12/07/2015

A breeder treats Montbéliarde dairy cows on a mobile milking dock in alpine pastures (Bauges Mountains, Savoie). © INRA, MEURET Michel
A breeder treats Montbéliarde dairy cows on a mobile milking dock in alpine pastures (Bauges Mountains, Savoie) © INRA, MEURET Michel

In light of the strong propensity to use avermectins in animal rearing, in the 1990s INRA researchers set out to explore the safety of animal products destined for human consumption. At the time in France, the use of ivermectin was not authorised in dairy cows, but was allowed during the drying-off period, on condition that the treatment be administered at least 28 days before calving(1).

Traces of ivermectin found in milk about two months after treatment

Researchers conducted experiments on dairy cows treated with ivermectin at recommended doses (0.2 mg/kg).

Analyses revealed traces of ivermectin in milk at concentrations close to plasma rates in treated cows as early as the first day following treatment, which suggests a high level of excretion of the drug by the mammary glands. Total quantity of ivermectin detected in milk after 18 days of treatment was estimated at more than 5% of the dose initially administrated. Researchers also observed that ivermectin continues to act as an insecticide in milk for 27 to 58 days after treatment, which exceeds the 28-day limit imposed by French regulations. British regulations are more in line with these results, since it stipulates a minimum of 60 days between treatment and calving.

Micro-doses of ivermectin against hypodermosis allows lactating cows to be treated

While these studies have had no bearing on French regulations, they have been useful in the fight against bovine hypodermosis, a parasitic disease caused by a type of fly whose larvae develop under the animal’s skin, causing abscesses. For this parasitic disease, previous studies have shown that “micro-doses” of ivermectin(2) are enough to eliminate the parasite. Researchers therefore verified that the quantity of residue found in milk immediately after treatment with micro-doses fell below the quantity tolerated by regulations (3). Based on their findings, the French food administration (DGAL) authorised the use of micro-doses of ivermectin in lactating cows, allowing a treatment programme for all cattle to eradicate hypodermosis (cf section 8).

(1) Cows have a drying off period of about two months per year, during which time no milk is produced. They can be treated then, provided the treatment takes place at least 28 days before calving, which triggers the production of milk once again. After calving, treatment is prohibited throughout the entire lactating period.

(2) Micro-dose: 0.002 mg/kg, i.e. 100 times less than recommended doses(0.2mg/kg).

(3) That is, the quantity of residue present in milk 28 days after treatment with 0.2mg/kg of ivermectin.

References

Toutain et al. 1988.  Kinetic and insecticidal properties of ivermectin residues in the milk of dairy-cows. Journal of Veterinary Pharmacology and Therapeutics 11-3  288-29.

Alvinerie et al. 1997. Résidus d'ivermectine dans le lait chez la vache laitière traitée pendant la période de tarissement avec la posologie recommandée par l'autorisation de mise sur le marché. Revue de Médecine Vétérinaire, 148 (2), 115-116.