Livestock farming is a crucial component of the global food supply chain, providing essential animal protein to meet the needs of a growing population. As the demand for meat, milk, and eggs rises, so does the pressure on farmers to increase production. In response to this demand, many farmers have transitioned from extensive to intensive livestock farming systems, where animals are raised in high-density settings to maximise output.
One of the key practices in intensive livestock farming is the use of antibiotics as growth promoters. Antibiotics are commonly administered to livestock to promote growth, prevent disease, and improve overall animal health. While this practice has benefits in terms of increased productivity, it has also raised concerns about the potential impact on public health and the environment.
In Australia, approximately 172 mg of antibiotics are used per kg of living or slaughtered animal in swine operations, 148 mg in chickens, and 45 mg in cattle breeding operations. These antibiotics are metabolised by the animals and eventually excreted in their manure. This excreted manure can then enter the environment and contribute to the spread of antibiotics in soil and water systems.
### Antibiotic excretion rates in livestock manure
Research studies have examined the excretion rates of antibiotics in different livestock species and their impact on the environment. Here are some key findings:
– In steers fed monensin, 75% of the antibiotic was excreted in faeces after 3 days, with no excretion via urine. Recovery rates reached 88-100% after 7-11 days.
– Beef cattle fed fluoroquinolones excreted 91% of the radioactivity, with 67.4% in faeces.
– Layer hens excreted ciprofloxacin at rates between 45% and 52% within 33 days.
– Broilers fed enrofloxacin excreted 74% of the antibiotic.
– Pigs excreted 96% of sulfadiazine after 10 days, with 44% in unaltered form.
The excretion rates of antibiotics can vary based on the species of livestock, how the antibiotics are administered, the antibiotic classes used, and the timing of manure collection. In general, it is found that injection bypasses the digestive tract and leads to lower absorption levels compared to oral administration via feed.
### Impact of antibiotics on manure treatment
Antibiotics present in livestock manure can have various effects on the environment, including impacts on biogas production during anaerobic fermentation. Sulfonamides do not significantly affect biogas yields even at high concentrations, while other antibiotics like danofloxacin and lincomycin/spectinomycin may impact methane production. Factors such as dry matter content, retention time, and incubation time can influence the performance of antibiotics in biogas production processes.
### Digestion, manure storage, and composting
During processes like anaerobic digestion and composting, antibiotics like trimethoprim and tetracyclines can be eliminated to varying degrees. Conditions such as temperature, solid particle content, and dilution with water can impact the elimination rates of antibiotics in manure. In composting studies, elimination rates are generally above 90%, indicating the potential for effective removal of antibiotics from the system.
### Rules for antibiotic administration
In light of the concerns surrounding antibiotic use in intensive livestock farming, it is essential for authorities to implement regulations to reduce the environmental impact of antibiotics in manure. This includes enforcing strict rules on antibiotic administration in livestock husbandry and setting maximum residue values for antibiotics in manure used for soil fertilisation. By taking proactive measures to address antibiotic use in livestock farming, Australia can help mitigate the potential risks associated with antibiotic resistance and environmental contamination.
In conclusion, the use of antibiotics in intensive livestock farming has both benefits and challenges. While antibiotics play a crucial role in maintaining animal health and promoting growth, their presence in livestock manure can have wide-reaching effects on the environment. By implementing responsible antibiotic administration practices and effective manure management strategies, farmers can help minimise the impact of antibiotics on the ecosystem and protect public health for future generations.
