Page 267 - The Welfare of Cattle

244 the WeLfare of CattLe

hormones in manure applied to agricultural fields and grazing cattle (Kuster et al., 2004; Kjar et al.,
2007; Kolodziej and Sedlak, 2007). However, little is known about transport paths and mobility
of hormones from livestock facilities and land application sites to water. However, under the 2005
final rule by the EPA, and current Nutrient Management Plan regulations, it is unlikely that feedlot
runoff would be capable of directly reaching water resources, though the risk of leaching cannot
be eliminated. However, the chance greatly increases as manure from these operations is applied to
crop and pasture lands.
Currently, the degradation pathways of hormones are not clearly defined. The fate of estrogen
conjugates is not well known, but it is often assumed that common fecal microorganisms such
as Escherichia coli are capable of hydrolyzing them via glucuronidase and sulfatase enzymes to
unconjugated forms (Belfroid, 1999); however, it is questionable if this assumption is valid for
estrogen sulfates since they are often observed in sewage treatment works (Ternes et al., 1999a;
Ternes et al., 1999b). Limited research has evaluated the stability of conjugated estrogens in
manure (Hanselman et al., 2003). Degradation studies of unconjugated estrogens in soil, water,
and manure have been conducted for several years, and the literature was recently reviewed by
Hanselman et al. (2003). Recently, Jones et al. (2007) demonstrated photolysis of 17β-estradiol,
testosterone, and progesterone by light in the UVA range (305–410 nm) in a phosphate-buffered
media at pH 5.5. Additionally, it was indicated that both progesterone and testosterone were directly
photolyzed, while 17β-estradiol was indirectly photolyzed in the presence of organic matter. The
effectiveness of a lagoon-constructed wetland treatment system for producing an effluent with a low
hormonal activity was recently investigated. Shappell et al. (2007) found that the nutrient remov-
als were typical for treatment wetlands: TKN 59%–75% and orthophosphate 0%–18%. Wetlands
decreased estrogenic activity by 83%–93% in the swine wastewater and estrone was found to be
the most persistent estrogenic compound. Constructed wetlands produced effluents with estrogenic
activity below the lowest equivalent E (17β-estradiol) concentration known to have an effect on fish
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(10 ng/l) (Shappell et al., 2007).

hOrMONeS aND NUtrIeNt USe

Producers are using hormonal growth promotants to stimulate improved performance in
cattle. Typically, this will include an improved lean tissue deposition with a concomitant decrease
in fat tissue deposition. This alteration in tissue deposition is also typically accompanied by
improved gain:feed by 10%–15% while also increasing intake (Rumsey et al., 1981; Rumsey,
1982; Rumsey, 1985; Rumsey and Hammond, 1990; Rumsey et al., 1999). Additionally, by shift-
ing growth to more lean tissue, which is rich in nitrogenous compounds, there is also a decrease
in urinary N (Cecava and Hancock, 1994). Most of these changes in nutrient excretion from
animals treated with growth promoting hormones are post-absorptive in nature and the ultimate
decrease in urinary N excretion may range from 1.67 to 10.43 g N/ animal/ day (Lobley et al.,
1985; Rumsey and Hammond, 1990; Cecava and Hancock, 1994; Lawrence and Ibarburu, 2006).
Since most of the urinary N is present as urea, it may be readily degraded to NH . In a closed
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chamber system, 14%–15% of total manure N and 2%–37% of urinary N volatilized over a 7-day
period (Cole et al., 2005; Archibeque et al., 2007). Due to the reactive chemical nature of NH ,
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this represents a nutrient loss from an operation in a form that can no longer be managed in open
air systems and may then subsequently react and cause changes in whatever ecosystem it may
later deposit. To help put this environmental benefit into perspective, if we consider the mean
reduction of urinary N to be 6.05 g/animal/day and that there are approximately 30 million
cattle that will be fed in feedlots each year in the U.S., by implanting 95% of these animals, then
approximately 172 tons of N would not be released into the environment each year, making this
a truly substantial impact.