Agriculture Reference
In-Depth Information
17
Emerging Contaminants in Livestock
Manure: Hormones, Antibiotics and
Antibiotic Resistance Genes
P. Ray, Z. Zhao and K.F. Knowlton*
Department of Dairy Science, Virginia Polytechnic Institute
and State University, Blacksburg, Virginia USA
Hormones in Manure as
Environmental Pollutants
Introduction
Most environmental concerns associated with
livestock farms focus on nutrients (nitrogen,
phosphorus) that impair the health of aquatic
systems or on pathogens that may lead to
food- or water-borne disease. In recent years,
however, other potential contaminants are
becoming of concern. Hormones (oestrogens,
androgens, progesterone and various syn-
thetic hormones) contained in livestock manure
have generated wide interest because of their
endocrine disrupting effects (Lange
et al
.,
2002; Hanselman
et al
., 2003; Lorenzen
et al
.,
2004). Similarly, the extensive use of anti-
biotics in animal agriculture and the develop-
ment of antibiotic-resistant bacteria are cause
for increasing concern. Livestock operations
are often cited as a reservoir for resistant bacte-
ria and antibiotic resistance genes (Chee-Sanford
et al
., 2001; Smith
et al
., 2004; Sawant
et al
.,
2007; McKinney
et al
., 2010), and antibiotic
use has implications for both animal and
human health. This chapter will focus on
these emerging contaminants in livestock
manure.
Endogenous steroidal hormones
Hormones are synthesized in specialized glands
of the endocrine system and are excreted at very
low quantities in urine and faeces (Meyers
et al
.,
2001; Lintelmann
et al
., 2003). The hormones
in animal manure that have important environ-
mental effects include oestrogens (oestrone,
oestradiol and oestriol), androgens (testoster-
one) and progestagens (progesterone).
An estimated 49 t of oestrogens, 4.4 t of
androgens and 279 t of gestagens were excreted
by farm animals in the USA in 2002 (Lange
et al
., 2002), and cattle production contributes
about 90% of oestrogens and gestagens and
40% of androgens. About 1500 kg oestrone and
oestradiol are excreted each year by farm ani-
mals in the UK (Johnson
et al
., 2006), about four
times more than the total oestrogens from
humans. These estimates are uncertain, as data
available may not be sufficient for accurate cal-
culation of the total mass of oestrogens excreted
(Hanselman
et al
., 2003). It is clear, however,
