Avoiding antibiotic residues in milk
Antibiotic or medicine residues in milk are unacceptable for two reasons. Firstly, there is a potential human health hazard and secondly, antibiotic residues can interfere with the manufacturing process inhibiting yoghurt and cheese starter cultures.
Ways to avoid antibiotic failure
There are many reasons why failures occur. It is estimated that one tank in a thousand has an antibiotic failure in the UK. The greatest majority of these are reported to the dairy company before the milk is collected and so this stops contamination of the tanker or supplies at the creamery. Most farmers know why failures have occurred and the majority of cases are due to human error.
A survey of farmers carried out by the Milk Marketing Board in 1981 identified the reasons they thought responsible for the failure and these are shown in Table 1. Not much has changed and these are still the main causes of failure today.
Table 1: Farmer survey on possible causes of antibiotic failure
|Reason||Percent of Farms
|Poor or no records
|Not withholding milk for the full period
|Calving early or short dry period
|Accidental transfer of milk
|Prolonged excretion of antibiotic
|Contamination of recorder jars
|Withholding milk from treated quarter/s only
|Lack of advice on withdrawal periods
|Recently purchased cows
|Milking through jars
|Use of dry cow therapy to treat lactating cows
It should be noted that the figures in Table 1 add up to over 100% as some farmers had more than one reason for possible failure. In addition to this list could be added accidental milking of dry cows where they run with the milking herd, poor identification of cows as some are not readily identifiable, and finally malicious contamination.
It can be seen that the greatest majority of the problems relate to the use of the product rather than the product itself. Just to put matters into perspective, over the past 10 years we have supplied over 500,000 dry cow tubes to our dairy clients. We have not had one incident where a failure was due to the product supplied.
It is important the following steps are taken to avoid contamination:
Any treated animal should be clearly identified to ensure the milk does not enter the bulk supply
Medicines must be administered in accordance with veterinary advice
Records must be kept detailing all treatment dates, medicines used together with the dosage administered, and the withdrawal periods for milk and meat
All milk from treated animals must be discarded. When treating cows with mastitis, many farmers only discard milk from the treated quarter believing that antibiotic residues remained only in this quarter. It should be remembered that there is a tremendous blood supply through the udder. For every litre of milk produced, 500 litres of blood flow through the udder. In cases of mastitis, the blood supply to the affected quarter will be increased as the body is trying to counteract infection. Antibiotic residues can enter the blood supply and be deposited in the untreated quarters resulting in a failure.
The withdrawal periods for animals treated with two or more preparations may differ from the periods listed when only one product is used on it’s own.
Ideally treated cows should be milked last through the parlour ensuring that the milk line is removed from the bulk tank. If this is not possible, then treated cows should be milked into a dump bucket. Many farmers milk treated cows into recorder jars and the milk emptied into a bucket. There are two potential problems here, firstly the valves at the bottom of the jar may leak and allow some of the milk contaminate the bulk supply. Secondly, antibiotics concentrate in butterfat and so if rings of fat remain in the jar, there may be enough residues left to contaminate the milk.
If animals calve early it is essential to check the date on which dry cow therapy was administered. Dry cow therapy contains antibiotic that is contained in a slow release base and the withdrawal periods for some products are over seven weeks.
Occasionally farmers have a failure that they are unable to explain and then ask us to investigate further. This is very easy to do, provided there are proper treatment records. In herds where no or incomplete records of medicine usage then we are unable to investigate the incident and the farmer will have to accept liability.
It is interesting that one of our clients had an antibiotic failure several months ago. He decided to appeal against the decision of the dairy company. He presented his medicine records, which recorded every treatment, together with his medicine purchase records as evidence. The records were so good and matched perfectly that the dairy company had no alternative but to compensate him for the milk that they discarded.
There is increasing pressure from the consumer to ensure that all milk supplied is free from residues of antibiotic or other medicines. There is no reason why any dairy farmer should have residue failures provided he observes the principles of medicine use correctly and milks cows in a way to avoid the accidental transfer of contaminated milk into the bulk supply.