Final answer:
The overuse of antibiotics in animal farming is primarily for enhancing production, leading to the selection of antibiotic-resistant strains that can be transferred to humans, posing severe public health risks.
Step-by-step explanation:
A primary reason for the overuse of antibiotics in animal farming is to enhance the production of livestock. In the United States, an estimated 70% of antibiotics produced are included in animal feed not to prevent disease but to promote growth. This routine use of antibiotics selects for antibiotic-resistant bacteria by killing susceptible bacteria while allowing resistant strains to survive and multiply. Consequently, the use of these drugs in livestock at low doses maximizes the probability that resistance will develop, and these resistant bacteria can then be transferred to humans, threatening public health.
Moreover, the rise of concentrated animal feeding operations (CAFOs) has led to the frequent use of antibiotics as a preventive measure against disease in closely quartered livestock, further exacerbating the problem. Indiscriminate use of antibiotics results in resistant bacterial populations like MRSA (methicillin-resistant Staphylococcus aureus) growing in prevalence, challenging the effectiveness of common treatments for infections in humans.