With a vast amount of data and rapid access to it (for example, through the Internet), some health professionals and consumers are asking questions about issues that range from environmental pollution to microwave radiation from recreational electronic devices. Agriculture and its food production practices are not immune from such public scrutiny. Consumers want a wide variety of products at reasonable prices and they also demand safe, wholesome, and nutritious food products. They question agricultural practices meant only to increase productivity and economic return.
Consumers are also concerned over the impact of drug residues in their food. Animal residues in animal tissues above the legal tolerance do have an impact on human health. Tolerances represent the maximal level or concentration of antimicrobial residues permitted in animal tissues at the time of slaughter. The existing evidence exposes the risks associated with drug residues in meat and poultry above the established tolerance.
Most residues of veterinary drugs occur in food at such low levels that they rarely pose a chronic or long- term health hazard. The importance of food safety through the reduction of residues in our food supply cannot be overemphasised.. Everyone who uses drugs on animals has a responsibility to ensure that their use does not result in drug residues in the human food chain.
There is need for the government and relevant institutions to ensure appropriate use of antibiotics in animals, and establish a national database to monitor microbe-related illnesses and trends in antibiotic resistance that may result from drug use in food animals.
In current agricultural practice, raising animals for food depends heavily on the use of drugs. The use of drugs in food animals is fundamental to animal health and for the economics of the industry. There are two sides to the issue of how drug use in food animals affects the health of humans: Reported benefits are derived largely from maintenance of good animal health and the reduced chance that disease will spread to humans.
But drugs used in food animal production and residues of those drugs could enter human food and increase the risk of ill health in persons who consume products from treated animals. Moreover, the use of antibiotics in food animals could contribute to the emergence of antibiotic resistant micro organisms in animals that could be transmitted to humans and result in infections that could be difficult to treat.
There are five major classes of drugs used in food animals:
• topical antiseptics, bactericides, and fungicides used to treat skin or hoof infections, cuts, and abrasions;
• ionospheres, which alter stomach micro organisms to provide more favourable and efficient energy substrates from bacterial conversion of feeds and to impart some degree of protection against some parasites;
• hormone and hormone like production enhancers (anabolic hormones for meat production and bovine somatotropin for increased milk production in dairy cows:;
• antiparasite drugs; and
• antibiotics used to control overt and occult disease and to promote growth.
Incidents of food ‘scare’ have become almost commonplace in recent years, fuelled by media speculation. Thus expressions such as salmonella, ‘mad cow disease’ listeriosis and bird flu are becoming familiar to public as well as to specialists in microbiology and agricultural science.
Antibiotic use with prescription or veterinary oversight is assumed to be, in general, highly accountable. As with many human drugs for which adequate directions can be written for the lay user, some food-animal drugs can be purchased over the counter without a prescription, usually from distributors of animal feed and other animal production supplies.
The accountability of use is improved when producers follow industry quality-assurance guidelines and, with the assistance of veterinarians, document the instances of drug use and the practices associated with drug use.
Residues of drugs used in the food animal industry threaten human health by being acutely or cumulatively allergenic, toxic, mutagenic, teratogenic or carcinogenic. There is inconclusive evidence that antibiotic residues transferred to humans through food might set up a biological milieu that favours the emergence of microbial strains within the host.
Current monitoring systems to detect drugs in milk, meat, and other food products derived from animals are inadequate. Screening and monitoring techniques should continue to be deployed to protect consumers against the possible adverse effects of ingesting residues of drugs, some of which could be toxic or may lead to diseases or allergic reactions. The accuracy of testing techniques should be improved to reduce the number of false-positive results that occur, especially in milk, and more resources are needed to develop testing methods for a wider range of drugs. Improved animal-management practices could substantially reduce the amount of drugs needed for food animals.
More research is needed on the impact of nutrition and drug treatments to boost immune function and disease resistance in animals. In addition, new vaccination techniques also are needed to prevent the spread of diseases. Effective vaccines will reduce the demand for antibiotics.
Issues concerning antibiotic use in food animals and humans should be coordinated with regard to use patterns, resistance trends, surveillance data, and recommendations for use in a partnership of regulatory agencies, pharmaceutical companies, the food animal industry, and animal and human health care professionals.
Alternatives to antibiotic use for maintaining animal health and productivity such as new vaccination techniques, improved animal nutrition, and genetic strategies must be sought. Existing alternatives should be implemented in a practical manner so that the appropriate uses of antibiotics and their effectiveness are maintained. Furthermore, risk factors in the development of resistance other than antibiotic use need to be better understood through increased research.
Additives are substances incorporated into animal feeds in order to influence the character of the feed or affect animal production. In the first category, one can list antioxidants, colorants, emulsifiers, stabilisers, thickeners, gelling agents, binders, anti-caking agents, coagulants, aromatic or appetising substances and preservatives. The main substances falling into the second category are vitamins, trace elements and medicinal compounds. Many of these substances are used in human foods and their addition to animal feeds is unlikely to give rise to concern.
The animal is, in effect, acting as a further safety buffer and few of the above chemicals produce residues in animal tissues. Concern has been expressed as to the possible effects of such residues in meat, milk and eggs on susceptible consumers.
Leading cause of residues in meat and milk was failure to observe withdrawal times. Other factors responsible for residues included exceeding the recommended dose, improper mixing of feed, feeding milk containing a drug to calves and mistaken administration due to lack of animal identification and record of treatment. Injectable drugs were more frequently involved with residues than prescription drugs.
The person who administers drugs and makes decisions on the sale of the animals was found to be responsible for the majority of the drug violations. All drugs should be used according to label directions.
All antibacterial preparations and many other drugs have a withdrawal time. This is the amount of time that must elapse after the last dose of the drug was administered to the animal before it can be slaughtered or any of its products used for food. Withdrawal times vary considerably depending upon the individual drug and the formulation of the drug that is used. There has been increased concern among consumers about antibiotic and other drug or chemical residues.
There has also been increased emphasis from the regulatory agencies to monitor and prevent residues. It is imperative that food animal producers utilise these programmes to improve their control on the use of antibiotics and drugs. This will help prevent any erosion of confidence in the milk and meat they produce and market.
The therapeutic use of medicinal substances is obviously essential to cure outbreaks of disease whenever they occur. As such treatment is carried out under the direction of a veterinary surgeon. No problems should arise for animals or humans, and particularly as such treatments will be spasmodic rather than continuous. However, residues can occur in animal products when large doses are administered immediately prior to slaughter, or in the milk of animals undergoing treatment. Micro organisms can mutate to develop or acquire resistance to antibiotic drugs.
Several questions determine whether this resistance will result in an increased hazard for humans: First, is the micro organism zoonotic; that is, can it cause a human disease by moving from the animal to a human?
Second, are there missteps in the normal safety procedures for processing and handling animal derived foods that are intended to reduce the risk of transmission of zoonotic micro organisms to humans, whether they are resistant to antibiotics or not? Third, if transmitted to humans from an animal source, is the micro organism more virulent than in its less-antibiotic-resistant form?
Fourth, if the micro organism is zoonotic, is the zoonosis treatable with other antibiotics? Finally, are there enough new antibiotics in development to substitute for antibiotics to which micro organisms have become resistant? How these questions are answered determines the extent of hazard to humans.