Emerging Contaminants in Livestock Manure: Hormones, Antibiotics and Antibiotic Resistance Genes - Sustainable Animal Agriculture

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in excretion rates (Schwarzenberger et al .,

1996). Table 17.3 shows the calculated total

daily excretion of oestrogens for cattle, pigs and

sheep (Lange et al ., 2002).

Degradation of oestrogens is a complicated pro-

cess and may include deconjugation, dissipation

and mineralization (Ternes et al ., 1999; Lee

et al ., 2003; Jacobsen et al ., 2005). Photo-

degradation has also been suggested as a mecha-

nism of oestrogen dissipation and mineralization

(Mitamura et al ., 2004; Feng et al ., 2005).

Conventional manure handling systems are not

designed to treat manure, but during prolonged

storage the degradation of hormones can occur

under anaerobic conditions.

Synthetic HGPs

As are endogenously produced steroidal hor-

mones, exogenous natural or synthetic hor-

mones administered to livestock are excreted in

faeces and urine (Schiffer et al ., 2001; Wilson

et al ., 2002). Zeranol and its metabolites appear

in manure, with concentrations highest imme-

diately after implantation (Baldwin et al ., 1983;

Dixon et al ., 1986; Jansen et al ., 1986). Zeranol

concentrations in manure declined steadily dur-

ing the period 20-70 days, but were still detect-

able 120 days after implantation. About 10%

and 45% of the implanted zeranol in steers was

excreted through urine and faeces, respectively

(Sharp and Dyer, 1972). Excretion of MGA is

primarily through the faeces, but little data are

available on persistence of excretion following

cessation of administration. Tracer studies using

radio-labelled MGA revealed that 60% of the

dose is excreted (intact or as metabolites) in the

faeces and 10% in the urine (Krzeminski et al .,

1981). For TBA, between 1.5 and 25% of the

dose is excreted (average 8%; Schiffer et al .,

2001), mostly as the metabolite 17a-TBOH

(Pottier et al ., 1981). This alpha form is the less

biologically active of the two primary metabo-

lites of TBA.

Degradation in storage

The concentration of E1, E2a and E2b was

475, 98 and 104 ng l −1 , respectively, in liquid

dairy manure stored in a lagoon for 8 months.

The total amount of all oestrogens in the stored

manure represented only 0.2% of estimated

accumulation of oestrogens during 8 months

of storage suggesting substantial degradation

of oestrogens during storage in the lagoon

(Zhao et al ., 2010). Oestrogen concentrations

decreased significantly in broiler litter at pH 5 or

7 after 1 week (Shore et al ., 1995).

Yang et al . (2010) reported the degradation

of steroid hormones (E2

, progesterone and tes-

tosterone) in swine manure by manure-borne

bacteria. Oestradiol, progesterone and testoster-

one were completely degraded by 9, 17 and 21 h,

respectively. In swine manure piles created over

5 days, the concentration of E1 was higher than

that of E2b (29.4 versus 0.64 mg kg −1 dry

weight) indicating the degradation or transfor-

mation of higher-degree oestrogens into E1;

thus the oestrogen profile of manure piles or pits

may not represent the actual proportion of oes-

trogens in fresh manure (Derby et al ., 2011).

The half-lives of the two metabolites of

TBA (17a-TBOH and 17b-TBOH) were 267 days

in liquid cattle manure (Schiffer et al ., 2001).

Melangerol acetate was relatively stable in

Degradation of steroidal hormones in

manure during storage

The ultimate fate of manure nutrients is strongly

influenced by how that manure is removed from

the animal facility and how (and whether) it is

stored; the same is true of steroidal hormones.

Table 17.3. Estimation of total daily oestrogen excretion by farm animals (μg day −1 ). Adapted from

Lange et al . (2002).

Species