Antibiotic use in domestic animals

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Antibiotics are extensively in livestock, fish, and plant production worldwide. The effect that this has on the environment is widespread. All manners of the environment are affected. The main affect on the Plantae is through eutrophication. The waste from the domestic animals contains antibiotic resistant bacteria which enters the soil and contributes to the nitrogen-fixing that is taking place. This increases the rate of eutrophication and so many of the nutrients in the soil are leached out far more quickly than they are being replaced. This is obviously detrimental to the plants that need to gain their nutrients from this soil. They struggle to gain the necessary levels for basic survival and so become weak and eventually die if the process continues. However, the area that is going to be focussed on in this essay is how antibiotic use in domestic animals affects the human environment. This is particularly relevant at the present time due to the recent outbreak of bird flu. This epidemic demonstrates clearly how easily animal diseases can be contracted by a human. Read about animal imagery in Volpone


The transfer of bacteria between species is more common that it at first seems. Over recent years microbiologists have been gathering evidence that suggests that resistant bacteria are passed from animal to humans with the result that humans are contracting more stubborn infections. Large volumes of antibiotics (50% of the total global consumption) are administered to food-producing animals for prophylaxis, treatment and growth promotion purposes. About 80% of these prescriptions have been reported to be unnecessary. The rising occurrence of antimicrobial-resistant infections in hospitals and the wider community has led to the question being raised as to the relationship between this growing resistant and the excessive use of antimicrobials in humans and livestock but more particularly in domestic animals such as cows, pigs, sheep, and chickens. The main aim in this piece is to ascertain whether the use of antimicrobial drugs in domestic animals contributes to the escalation of antimicrobial resistance in humans.

The Theory behind the Spread of Resistant Strains of Bacteria

The rapid spread of the resistant forms of bacteria relies is a perfect example of the natural selection theory that was pioneered by Darwin. This theory states that those organisms adapted to the surrounding environment the best (both in feeding habits and body form, such as having thick fur in a cold place or being camouflaged correctly for a particular background) will survive to reproduce whilst those less well adapted die before having a chance to mate and reproduce. In this way genes that increase the likelihood of survival and so reproduction increase in frequency and so become better established in the gene pool from generation to generation. This process happens in all species but takes place particularly quickly in bacteria.

Bacteria multiply by a process known as binary fission. This is when a single celled organism divides into two smaller ‘daughter’ cells. It is a form of asexual reproduction and can take place in bacteria as regularly as every twenty minutes. Therefore if only one in a large colony of bacteria is resistant to the drug, then all the others will be destroyed leaving the single bacterium to multiply and produce a completely new strain that will no longer respond to antibiotic treatment. The over use of antibiotics has meant that more and more bacteria are mutating and becoming resistant to a wider range of limited antibiotics.

The Economic Reasons behind the Problem

Traditionally, Britain has been a farming nation with large part of its economy being drawn from this source. During the Second World War, when import channels from the colonies but also from other places such as those from America and Europe were greatly reduced due to attack from the Germans, the British relied heavily on what farmers could produce for the entire population. The government realised that were the country not to starve the efficiency of home agriculture must be bettered. It became imperative to increase return to the maximum point. To this end measures were taken to boost the fertility of the soil (use of fertilizer) and the yield of the livestock. It was at this point that intensive farming became common practice.

Before this animals were given plenty of space and allowed to roam free in large fields, foraging for food themselves. However the land would not be able to support the numbers of animals being introduced so new techniques were adopted. Now animals were kept in close confinement and fed at regular intervals. Traditionally chickens had been allowed to roam over the farmyard but this limited egg production and it was found to be far more economically sound to keep them in batteries. More eggs were produced and less manpower was needed to gather them. However, this collection of large numbers of farm animals in one place for long periods of time had its disadvantages. Disease was able to spread quickly throughout the herd so farmers needed a way of controlling this.

In the 1950’s the discovery was made that animals could be made to grow more quickly if antibiotics were fed to them. This method had the advantage of helping to control the rising spread of disease and so seemed like a perfect option. The increase in growth can be explained in the following way: all mammals harbour bacteria in their gut. Just like any organism, bacteria needs nutrients and in the gut the only way it can get them is to be a competitor for nutrients that would otherwise go to the host.

In a bacteria-free environment (such as was developed in the animals that were fed the antibiotics every day) all nutrients are available to the animal (host) and so it is able to grow faster. The theory also exists that the presence of the antibiotics in the bloodstream of the animal prevents any number of “sub-clinical” diseases. It is thought that these diseases may cause periods of malnutrition absorption and so stunted growth will arise. Amyes, SGB. (2001) Magic Bullets, Lost Horizons. The Rise and Fall of Antibiotics. Taylor and Francis, London. At this point there was no restriction on which antibiotics should be used for intensive farming and so all were tried and most were found to be effective, with the concentrations being used increasing as the benefits were realised.

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