The presence of residues may result from failure to observe the mandatory withdrawal periods, illegal or extra-label use of drugs and incorrect dosage. It is evident from several studies that many animal-derived foods have unacceptably high levels of drug residues. Education on prudent use of antibiotics has been observed to be particularly lacking amongst dispensers and prescribers of antibiotics, writes C.Pandiyan.


Now a day’s consumer safety with regard to food is highly mandatory. The safety of food is threatened by various agents like pathogenic microorganisms, aflatoxins, pesticides, and antimicrobial agents. Pathogenic microorganisms constitute the most important food-related threats to public health. The occurrence of antibiotic residues in milk intended for human consumption is undesirable for a number of reasons such as, cause allergic reactions, the incidence of bacterial resistance, disrupting of the balance of gut microflora, carcinogenesis, mutagenesis and malformation risks. In addition, the presence of antibiotic residues in milk used in the dairy industry can have adverse effects on the production of fermented dairy products such as yogurt and cheese.

Generally, the antibiotic and drug residues are remnants of antibiotic drugs or their active metabolites that are present within animal tissues or products. The quantity of drug and their metabolites may persist at unacceptable levels and leads to serious health problems to the consumers. The use of antibiotics to bring about improved performance in growth and feed efficiency, to synchronize or control of the reproductive cycle and breeding performance also often lead to harmful residual effects. A withdrawal period is established to safeguard humans from exposure of antibiotic added food. The withdrawal time is the time required for the residue of toxicological concern to reach safe concentration as defined by tolerance.

Varieties of antibiotics

The antibiotics used in veterinary medicines belong to six major groups. Those are (i) Beta-lactarns (eg: penicillin), (ii) aminoglycosides (eg: gentamycin), (iii) tetracyclines (eg: oxytetracycline), (iv) macrolides (eg: erythromycin), (v) quinolones (eg: fluroquinolone), and (vi) sulphonamides eg: trimithropin). Any of the drugs belonging to these groups can appear in the milk.

When the milk is collected from several thousands of farmers, small quantities of contaminated milk from treated animals would be pooled with a very large volume of uncontaminated milk resulting in undetectable amounts of antibiotic residues in bulk milk. The antibiotic residues in food of animal origin produce potential threat to direct toxicity in human and second is whether the low levels of antibiotic exposure would result in alteration of microflora, cause disease, and the possible development of resistant strains which cause failure of antibiotic therapy in clinical situations.

Application of antibiotics on dairy animals

Treatment of infected quarters using antibiotics is one practice used to control mastitis. In dairy animals, the drugs are administered for treatment of mastitis through intra-mammary or intravenous infusions. The presence of residues may result from failure to observe the mandatory withdrawal periods, illegal or extra-label use of drugs and incorrect dosage. It is evident from several studies that many animal-derived foods have unacceptable high levels of drug residues. Education on prudent use of antibiotics has been observed to be particularly lacking amongst dispensers and prescribers of antibiotics. There is particularly limited information on the consequences of residues in terms of public health implications and bacterial resistance. Also, due to prevailing harsh economic conditions, farmers are known to allow only a 1-day withdrawal period for milk regardless of the type of antibiotic used. In order to safeguard human health, the World Health Organization (WHO) and the Food Agriculture Organization (FAO) have set standards for acceptable daily intake and maximum residue limits in foods.

Antibiotic residues in milk

The prevalence of antibiotic residue in milk products had been observed due to indiscriminate use of various antibiotics in the treatment of mastitis. Use of penicillins, tetracyclines, sulphonamides, and aminoglycosides was most frequently used in lactating animals, which led to the occurrence of their residues in milk. Antibiotics used as therapeutic agents or as a feed supplement in the milch animal lead to the secretion of their residue in milk. These residues not only create problems in the dairy industry but also have immense public health significance.

The presence of antibiotic residues in milk is influenced by the following factors:

  • concentration and type of antibiotic used,
  • carrier employed in the preparation of antibiotic,
  • amount of milk drawn from the gland,
  • time interval between treatment and milking,
  • absorbance of udder tissues,
  • milk yield g. individual factors.

Less awareness of withdrawal times or deliberate abuse may lead to elevated levels of drug residues in the milk. The most common causes of occurrence of drug residues in milk are insufficient identification of treated cows, insufficient knowledge about withdrawal periods and failures due to hired staff.

Effect of non-restricted use of antibiotics in dairy animals

Public health aspects: Human health problems that may result from intake of subchronic exposure levels include allergic reactions in sensitive people, toxicity, carcinogenic effects although the validity of some of the reactions is sometimes debated. Penicillins especially, as well as other ß-lactam antibiotics such as cephalosporins and carbapenems, could cause allergies if high levels of residues persist in milk consumed by penicillin-allergic persons. Penicillin is not inactivated by pasteurization or drying and levels as low as 0.03 IU/ml has caused skin rashes. Tetracyclines residues also have the potential to stain the teeth of young children. Tetracyclines can react with nitrite to produce nitrosamines which is a carcinogen. The non-restrictive usage of antibiotics in animal rearing may lead to problems due to the presence of harmful residues in foods and raw materials of animal origin.

Technological problems in dairy foods: The dairy starter cultures are mainly lactic acid bacteria used in the production of a range of fermented milk products, including cheese, yoghurt, cultured butter, and cultured milk. The primary role of starter cultures in cheese manufacture is the production of lactic acid from lactose at a consistent and controlled rate. The consequent decrease in pH affects a number of aspects of the cheese manufacturing process and ultimately cheese composition and quality. Antibiotic residues in milk are undesirable from a manufacturing perspective, as they can interfere with starter culture activity and hence disrupt the manufacturing process. The concentrations of antibiotics which would cause such effects is however often higher than would be found inherent as residues in milk. The sensitivity of starter cultures to antibiotic substances present in milk also varies considerably. Even within the same species of culture strain, differences in sensitivity are evident. Further, the response of starter cultures to residual antibiotics in milk destined for cheese or yoghurt manufacture can also be affected by the presence of other natural potential inhibitors.

The antibiotic residues in milk are of concern in two respects. First, they may curtail proper lactic acid fermentation in cultured products resulting in spoilage and the possibility that staphylococci may proliferate before curd formation. Secondly, the ingestion of antibiotic-contaminated milk may cause a reaction in human already sensitized to the contaminants.

The potential hazards of ingesting antibiotic residues in contaminated milk include “allergic reactions, interference in the intestinal flora and resistance population of bacteria in the general population. Allergies to antibiotic occur when the body’s immune system attacks the antibiotic, which is often a haptenic metabolite of the antibiotic and some carrier tissues. Small levels of antibiotics can be very hazardous to susceptible humans causing acute to severe reactions. Penicillin raises most apprehensive in this respect because it strongly inhibits lactic acid bacteria and because it may trigger anaphylactic shock in unusually sensitive patients to whom it has been administered previously. Other antibiotics may cause similar reactions but evidence indicate that penicillin is of great concern. It has been suggested that the present recommended a limit of 0.05 IU of penicillin/ml of milk is too high and offers no guarantee of safety. The presence of even small quantities of antibiotics in milk is found to create problems in the dairy industry.

The commonly encountered problems are a. Inadequate curdling of milk and improper ripening of cheese during their production, b. Decreased and flavour production in cultured products, c. Interferences with starter culture resulting in loss of production. Antibiotic residues may cause partial or complete inhibition of starter cultures used in fermentation, leading to interference in the production of fermented products like Yogurt and cheese, d. Difficulties in validation of certain quality control test.

General precautions to prevent antibiotic residues

  • Establish a valid veterinarian-client-patient relationship to ensure proper diagnosis and treatment of disease.
  • Maintain milk quality and implement an effective mastitis management program to reduce the use of antibiotics.
  • Implement employee training and awareness of proper animal drug use.
  • Only use approved over-the-counter antibiotics, according to label instructions, and approved prescription antibiotics which have the proper label.
  • Use drug residue screening tests specific to the drug utilized before marketing milk and/or meat from treated animals.
  • Do not use drugs that are specifically prohibited for use in milking, dry, or growing animals.
  • Segregate and milk treated animals after, or in a separate facility from, all non-treated animals to ensure that milk is not accidentally commingled.
  • If in doubt about residue status, do not market milk and/or dairy beef from treated animals.

The introduction of organic dairy products will be highly mandatory to safeguard the health of consumers. Organic dairy must be from animals that have been under continuous organic management for at least one year prior to the production of the milk or milk products. Superiority in terms of quality of products: Organic Milk is better for Health: Milk is a perfect indicator that reflects the level of pollutants and pesticides those contaminated dairy cows and as well as dairy. Conventional milk may contain residues of hormones that used on the dairy animals pesticides, antibiotics, urea, solvents, which have a serious impact on the individual’s health. In conventional dairy farms, such practices were common to obtain more milk beyond their natural capacity. Inappropriate protein is fed to cows for stimulating the rapid growth or milk production. All these factors make conventional milk inferior in quality. Consumption of such milk may lead to early puberty, hypersensitivity, hormonal imbalance, and certain types of cancer in humans. Milk from organic and non-organic dairies is having a difference but organic milk is far superior to non-organic milk.

Here are the differences which make organic milk superior:

CLA: milk contains Conjugated Linoleic Acid (CLA). The function of CLA in the human body is to boost the immune system and reduce the growth of tumors. CLA levels in organic milk are higher because these cows eat greater amounts of grass, hay, and silage.

Pesticides: Organic dairy farms don’t use any artificial pesticides on pastures where cows graze. It has more effects on the children because of their immature organ and immune systems.

Antibiotics: On conventional dairy farms, cows are given antibiotics routinely to prevent disease and infection. While on organic dairy farms first natural remedies are used for cow’s illness, if it won’t work then antibiotics are given. When an organic cow needs to be treated with antibiotics then the ‘withdrawal period’ is considerably longer than that recommended for conventional farming.

GMOs & Solvents: The feed given to cows on organic dairy farms is free from GMOs (Genetically modified organisms), solvent extracts and urea. So it results in milk that is free from these substances.

Hormones: Fertility hormones are used routinely in conventional dairy farms to ensure that calves are conceived and born within defined management periods and also to synchronize batches of cows or heifers to calve around the same time. Hormones such as rBGH (Recombinant Bovine Growth Hormone) and Oxytocin were often used to increase milk production and cause easy letdown of milk respectively. While on organic dairy farms, the use of hormones was totally prohibited.

In India, The National Programme on Organic Production (NPOP) (under The Agricultural and Processed Food Products Export Development Authority (APEDA)) was officially launched in 2000 and notified under FTDR (Foreign Trade Development & Regulation) Act in the year 2001. The National Programme for Organic Production (NPOP) proposes to provide an institutional mechanism for the implementation of National Standards for Organic Production, through a National Accreditation Policy and Programme.

The aims of the National Programme for organic production, are: (a) to provide the means of evaluation of certification programmes for organic agriculture and products as per the approved criteria. (b) to accredit certification programmes (c) certification of organic products in conformity to the National Standards for Organic Products. (d) to encourage the development of organic farming and organic processing.