Agriculture Reference
In-Depth Information
Table 17.2.
Chronology of the use of anabolic agents in the US cattle industry.
Year
Event
1956
Oestradiol benzoate/progesterone implants approved for steers
1958
Oestradiol benzoate/testosterone propionate implants approved for
beef heifers
1968
Oral melengoestrol acetate approved for beef heifers
1969
Zearnol implants (36 mg) approved for cattle
1982
Silastic oestradiol implant approved for cattle
1984
Oestradiol benzoate/progesterone implants approved for beef calves
1987
Trenbolone acetate implants approved for cattle
1991
Oestradiol/trenbolone acetate implants approved for steers
1993
Bovine somatotropin approved for use in lactating cows
1994
Oestradiol/trenbolone acetate implants approved for use in heifers
1995
72-mg zeranol implants approved for beef cattle
1996
Oestradiol/trenbolone acetate implants approved for stocker cattle
implant either alone or coupled with E2b.
Zeranol, also called a-zearalanol, is a resorcylic
acid lactone. Zeranol mimics the action of E2b
and is often implanted as the sole compound.
Melengoestrol acetate is administered as a feed
additive, while all the other HGPs are adminis-
tered as implants and can be used for oestrus
synchronization and/or lactation induction in
cattle as an active gestagen (Funston
et al
.,
2002). It is also fed to feedlot heifers to improve
feed efficiency and weight gain (Kreikemeier and
Mader, 2004).
suggesting contribution of the livestock industry
to the environmental load of hormones. In early
lactation cows, urinary excretion of total oestro-
gens was 174 mg day
−1
(Erb
et al
., 1977). In the
5 days prior to parturition, concentrations of E1,
E2a and E2b in dairy faeces were 11.6, 60.0 and
33.6 ng g
−1
dry sample (Hoffmann
et al
., 1997).
Three of four major oestrogens, E2a, E2b and E1
were detected in fresh faeces of both dairy and
beef cattle (Wei
et al
., 2011). Oestrone was the
most prevalent in dairy faeces (101-865 mg kg
−1
dry weight) while the concentration of E2a
and E2b ranged from <1.1 to 1113 and from
<1.9 to 485 mg kg
−1
dry weight, respectively.
Concentrations of these three hormones were
lower in beef cattle faeces than in dairy faeces
(<5.0-508, <1.1-260 and <1.9-243 mg kg
−1
dry weight for E1, E2a and E2b, respectively).
In cow manure, natural oestrogens were present
at concentrations of 6, 17 and 16 ng g
−1
dry sol-
ids for E2a, E2b and E1, respectively (Andaluri
et al
., 2011).
Oestrogens are also detected in poultry
manure with E2b being the most prevalent form
followed by E2a and E1 (150, 93 and 44 ng g
−1
dry solid, respectively; Andaluri
et al
., 2011).
Oestrogen content (oestradiol or oestradiol plus
oestrone) of dry broiler litter of 28-30 ng g
−1
has been reported (Casey
et al
., 2004; Shore
et al
., 1995). The concentration of E1, E2b and
E2a in pig slurry was 243, 115 and 9 mg kg
−1
,
respectively (Laegdsmand
et al
., 2009). Factors
such as age, diet, season, health status and
diurnal variation may contribute to variation
Excretion of steroidal hormones
Oestrogens
Oestrogens are mainly excreted through urine
and faeces. In faeces oestrogens mainly exist
in free forms, while in urine oestrogens are
mostly conjugated (Shore and Shemesh,
2003). Free and conjugated forms of oestrogen
(17a-estradiol (E2a), E2b and oestrone (E1))
account for more than 90% of the excreted
oestrogens in cattle (Hanselman
et al
., 2003),
but E2a is rarely excreted by swine and poultry.
In cattle, 58% of the total oestrogen excretion is
via the faeces (Ivie
et al
., 1986), while swine
and poultry excrete 96% and 69% of oestrogens
in urine, respectively (Ainsworth
et al
., 1962;
Palme
et al
., 1996).
There are several reports of the presence
of steroidal hormones in animal manure
