All stock remedies and veterinary medicines need to be approved by either the Department of Agriculture or the Department of Health before they may be imported, manufactured or sold in South Africa. When these products are intended for use on food-producing animals, the scientific dossier submitted for approval must also contain detailed data on:
- The acceptable daily intake (ADI) for humans – the calculation of which has a 100x to 1 000x safety limit built into it.
- Maximum residue levels (MRL) for various tissues such as meat, fat, milk etc. which is based on the ADI.
- A withdrawal period, which is the period between the last treatment for that remedy or medicine and when the tissues may be regarded as safe for human consumption. This period is determined through performing trials and measuring the residues in the tissues.
The approved withdrawal period is always printed on the label and/or on the package insert for the different tissues and different species for which the remedy or medicine is intended. It is a criminal offence to ignore this withdrawal period and slaughter an animal for human consumption before the withdrawal period has expired.
All this is simple to follow for domestic animals for which this data has been generated. However, some of the remedies used on game have:
- Not been registered for use on game animals.
- The data has not been generated.
Some of the products used on game are also used on domestic stock, so there is information on the withdrawal period for cattle, sheep and goats, cattle pour-ons for tick control, cattle or sheep anthelmintics (dewormers). As there are species differences in how drugs are metabolised, the withdrawal period cannot just be extrapolated to game species. For safety sake, therefore, one should add at least 50% to the withdrawal period on the label for domestic animals, e.g. if the recommended withdrawal period for an anthelmintic for cattle is four days, one should not slaughter a game animal for meat within six days of it being treated with that same remedy.
Some products, like the immobilisers, e.g. M99 (etorphine), was never intended to be used on animals for human consumption. The necessary ADIs, MRLs and withdrawal periods have not been determined.
Strictly speaking, therefore, it is illegal to use an animal that has been treated with such veterinary medicines for slaughter for meat. Practically speaking though, the ½ life of M99 in some game species seems to be about 240 hours or 10 days, so for safety sake a withdrawal period of two months (6x the ½ life) from the time an animal was darted until it may be shot for human consumption should be implemented. Veterinarians who immobilise and/or tranquilise game animals often use a cocktail of drugs, making this aspect even more difficult to advise on.
So our advice is as follows:
- Always remember to ask your vet what his recommended withdrawal period is for the treatment he has administered.
- Adhere to a withdrawal period after treatment and before slaughter of 50% longer than is recommended for domestic animals on the label recommended for domestic animals when administering stock remedies.
- If you must slaughter an animal that was treated with M99, wait at least two months before slaughtering that animal for human consumption.
- Keep accurate and detailed records of all animals treated with any stock remedy or veterinary medicine and inform the purchaser of these animals of the treatment history in writing.
Dr Peter Oberem: WRSA Vice President