Environmental Hazards Created
by Livestock Farming
The environmental hazards that need to be managed in
livestock farming include:
●
pollution of open waterways with dung and urine
●
pollution of groundwater with dung and urine
●
changes in the composition of water leading to
poisoning of aquatic life
●
soil erosion
●
aerial pollution including unpleasant odours
●
dust emission
●
inappropriate disposal of dead stock
●
noise
●
encouragement of flies and other unwanted animals
●
release of agro- and veterinary chemicals
●
destruction of particular plants
Ammonia accumulation is the predominant environmental
hazard in intensive livestock farming. Release of ammonia is an environmental hazard
because of:
●
smell
●
indirect effects of ammonium cation deposition from
the atmosphere on:
●
conversion of moorland into low-value grassland
●
tree damage
●
leaching of potassium, magnesium and calcium cations
from soil and leaves
Ammonia is implicated in three animal health and welfare
features. They are:
●
skin lesions such as hock burn
●
chemical degradation of hoof keratin and subsequent
lameness
●
inhalation of ammonia, and respiratory tract damage
and disease
Industrialized and intensive livestock farming systems
need to reduce emissions of atmospheric ammonia in order to comply with
international environmental standards. Most of the ammonia comes from feeding
high-protein feeds. For example, about 60 to 70% of the nitrogen in pig rations
is excreted in faeces and urine. The nitrogen in faeces is mainly present as
protein, and nitrogen in urine is mainly in the form of urea. One way of reducing
ammonia emission is to reduce dietary protein levels. This may involve some
sacrifice in growth performance of the animals, but there can be a cost saving
as protein is one of the more expensive feed components.
Ammonia emissions from urine occur when urea is
hydrolysed by the enzyme urease. This enzyme is abundant in topsoil, in
livestock bedding and on concrete floors. Ammonia release can be particularly
pronounced with straw bedding systems ( Jeppsson, 1999), but emission rates as high
as 1 g NH
3
/m
2
/h have been recorded from concrete
floors in cattle barns (Braam
et al
., 1997).
Ammonia can be toxic and it has a remarkably rapid
uptake rate into tissues. It is fat-soluble when in its non-ionized form, and
water-soluble when present as the ammonium cation. Its fat solubility allows
very rapid uptake by cell membranes and subsequent cell poisoning, and its
water solubility as NH
4
+
allows prompt irritation of moist tissue
surfaces, such as the cornea and upper respiratory tract. Calves and cattle
avoid putting their muzzles on bedding in the normal sleeping position if the
ammonia concentration in bedding is high (Fig. 1.2). As a result they may spend
less time sleeping.
Fig. 1.2.
Normal posture in cattle during deep
sleep.
Ways of reducing ammonia emissions include:
●
reducing nitrogen intake in livestock feed
●
lowering the temperature of stored effluent
●
covering stored effluent
●
reducing the pH of stored effluent or manure within
animal houses
●
drying manure promptly
●
prompt dilution of effluent with water
●
direct incorporation of effluent into soil, instead
of broadcasting
In aquatic species, high ammonia concentrations in
water reduce the excretion rate of ammonia from gills and increase the uptake
of ammonia. This can lead to systemic elevations in ammonia concentration in
the haemolymph, reduced concentrations of the respiratory pigment haemocyanin and
suppressed oxygen transport. These effects are compromised further by the
increased oxygen consumption rate associated with a switch from anaerobic
carbohydrate metabolism to lipid metabolism during ammonia intoxication. In
spite of this, fish do not always react negatively to ammonia in water.
Sometimes they enter water containing appreciable concentrations of ammonia,
even at levels which can lead to poisoning and death (Erichsen Jones, 1952).