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Antimicrobials are agents that kill, or stop the growth of, microorganisms such as bacteria, viruses, fungi, parasites and protozoa. Antibiotics are commonly used to treat bacterial infections in humans and animals. Coccidiostats are also routinely used, especially in poultry production to prevent infections with protozoa including a disease called coccidiosis. Many microorganisms are normally found in different parts of the body including skin, mouth, gut and nose. Infections can be caused by changes in microorganisms normally found in the body or by new ones invading the body from other sources such as the soil, water, infected animals or people.
Resistance to antimicrobials occurs when microorganisms continue to grow in the presence of antimicrobial levels that would normally stop their growth or kill them. This can happen when farm animals are routinely given antimicrobials in their food to improve gut health and therefore growth, often at concentrations lower than those used to treat diseases. The World Health Organization states that this practice accelerates the spread and emergence of antimicrobial resistance in humans which is an increasing global concern. The WHO has also developed guidelines on the use of medically-important (for humans) antimicrobials in food-producing animals.
The use of low dose antibiotics for growth promotion has emerged with the intensification of livestock production. It is unclear how low doses of antibiotics improve growth rates in animals. One theory is that antibiotics reduce the total number of bacteria in the gut, which means that there is less competition between bacteria/microorganisms and the animal for nutrients entering the gut which the animal needs for growth. Continued use of antimicrobials over time, can lead to an animal’s bacterial populations becoming resistant to the antimicrobial.
Low doses of antimicrobials can also aid in control and prevention of animal diseases in food animals. However, this type of use of antimicrobials should not replace good management practices.
The key risk factors for diseases that may require antimicrobial use in farm animals include: stress; low immunity; overcrowding; overheating; poor hygiene and biosecurity (processes to prevent new infections being introduced); diet change; housing system; mixing of unfamiliar animals; group size; temperature variation, and poor air quality. Meeting animals’ needs for space, appropriate food and water, comfort and ensuring appropriate handling and management practices, including regular inspections of animals, can help prevent disease and significantly reduce any need for antimicrobials. This can be achieved by considering the following: low-stress stock handling; reducing stocking density; implementing an all-in all-out system (every animal in a batch leaves the farm at the one time and all new animals enter at the one time); vaccination; effective shed design and ventilation; appropriate feeding; avoiding mixing unfamiliar animals; breeding for robustness; and avoiding use of antimicrobials except to treat sick animals under veterinary advice.
The RSPCA supports responsible use of antimicrobials, particularly of those important for human medicine. Routine use of antimicrobials (for growth promotion or to prevent infections), especially antibiotics and coccidiostats, is strongly discouraged as the focus of farm animal management must be on creating an optimum environment to meet the animals’ needs.
Where antimicrobials are routinely used to prevent the spread or occurrence of disease in farm animals, an Antimicrobial Stewardship Plan (which includes veterinary advice) should be in place and updated yearly, to demonstrate responsible antimicrobial use. The Plan would demonstrate that a greater focus was placed on optimising the animal’s environment, good animal husbandry and appropriate management practices to reduce reliance on routine use of antimicrobials and to eventually end their use altogether.
Reporting antimicrobial use (including coccidiostats) by every livestock sector should be compulsory, as it would provide transparency to consumers and allow industry to demonstrate a commitment to responsible antimicrobial use. Monitoring through testing animal products and reporting of antimicrobial resistance is also needed to evaluate the effect of reducing the use of antimicrobials on the level of antimicrobial resistance.