This study showed that both on the sow and
fattening pig farms the use of antibiotics on individual
farms is relatively stable over the 4 yr of the study period
(variation due to year relative to variation due to
farm is very low). In other words, farms that use greater
amounts of antibiotics in 1 yr will also do so in the
next year, whereas farms that use decreased amounts
in a particular year may also use less in the other years.
Our study showed that antibiotic use, both on sow
and fattening pig farms, was mainly influenced by farm
system and number of pigs present on the farm, and
for sow farms only, antibiotic use was also affected by
the population density in the region of the farm. The
greater number of pigs present on the farm may result
in a greater probability of infection, which can explain
the increased antibiotic treatments on large farms. Increased
infection at larger farms has been reported previously
(Österberg et al., 2006; Hautekiet et al., 2008;
García-Feliz et al., 2009).