Agriculture Reference
In-Depth Information
together on the same genetic element from iso-
lates obtained from Danish pig herds (Aarestrup
et al
., 2000). Thus, it is critical to consider co-
selection of antibiotic resistance across antibiotic
classes in evaluating impacts of feed antibiotics.
benefit from antibiotic inclusion (Thames
et al
.,
2012), while those fed traditional milk replacers
usually show improved growth and health
(Quigley and Drew, 2000; Berge
et al
., 2006;
Stanton
et al
., 2010). Also, quality and quantity
of colostrum feeding influences the benefit of
antibiotic addition (Kaneene
et al
., 2008). In situ-
ations where management or nutrition is not
optimal, health benefits with milk replacer medi-
cation may be more apparent.
The FDA approved the ionophore monensin
for use in lactating cows in 2004, partly because
of improvements in cow health. Monensin has
been shown to reduce the incidence of clinical
ketosis, reduce the duration of subclinical
ketosis, reduce the rate of new mastitis infec-
tions and reduce the incidence of displaced abo-
masums (McGuffey
et al
., 2001). Ionophores
also contribute to control of protozoa that cause
coccidiosis in poultry and calves.
Sub-therapeutic antibiotics and
animal health
Effects of sub-therapeutic antibiotic use on animal
health have been difficult to assess and the general
consequences of antibiotic amendment in live-
stock feed are complex (Marshall and Levy, 2011).
Based on medicated feed prescription rates,
decreased rates of respiratory infections were
observed in Swiss piglets and fattening pigs in the
3 years following the antibiotic ban relative to the
3 years prior, but gastrointestinal tract infections
appeared to go up (Arnold
et al
., 2004). A marked
increase in necrotic enteritis was noted in broiler
chickens in Norway following the avoparcin ban,
but this seemed to be ameliorated by the subse-
quent approval of narisin as a feed additive (Grave
et al
., 2004). Also, while therapeutic antibiotic use
rates did indeed decrease in Switzerland (Arnold
et al
., 2004), Norway and Sweden (Grave
et al
.,
2004) following the EU ban, therapeutic use
increased in weaning piglets in Denmark (Grave
et al
., 2004). Generally, a comprehensive exami-
nation of banning sub-therapeutic antibiotic use
in piglets, beef cattle and poultry in Sweden indi-
cated that although temporary health problems
and increases in antibiotic uses were noted, strate-
gic management practices make possible competi-
tive animal production and reduced antibiotic use
(Wierup, 2001).
The effect of milk replacer medication on calf
growth and health depends partly on the nutrient
density and intake of milk replacer. Calves fed
nutrient-dense 'accelerated' milk replacers did not
Conclusions
The environmental effects associated with hor-
mones and antibiotics from livestock farms have
induced great interest and concerns in scientists,
governments and the general public. Oestrogens,
androgens and progestagens have been detected
in some US rivers (Kolpin
et al
., 2002) and may
cause endocrine disrupting effects, especially in
aquatic species. Antibiotics have also been
detected, in ppb or ppt concentrations in ground
and surface water. Although degradation of both
hormones and antibiotics occurs during manure
storage and after land application, more research
is needed on effective approaches to reduce load-
ing of these from livestock farms. Also, more work
is needed on the environmental fate, potency and
biological effects of these compounds originating
from livestock farms.
References
Aarestrup, F.M., Agerso, Y., Gerner-Smidt, P., Madsen, M. and Jensen, L.B. (2000) Comparison of antimi-
crobial resistance phenotypes and resistance genes in
Enterococcus faecalis
and
Enterococcus
faecium
from humans in the community, broilers, and pigs in Denmark.
Diagnostic Microbiology and
Infectious Disease
37, 127-137.
Ainsworth, L., Common, R.H. and Carter, R.L. (1962) A chromatographic study of some conversion prod-
ucts of estrone-16-C-14 in the urine and feces of the laying hen.
Canadian Journal of Biochemistry
and Physiology
40, 123-135.
