Download The effects of ozone depletion on farm animal welfare

The effects of ozone depletion on farm animal welfare and
health
Ozone plays a critical role in shielding the
earth's surjiace from the lethal arid dainagiiig
effects ofirltrazdet (UVI radiation from the
sun. Emissions c~ch/oroflirorocarbons(CFCs)
kazlr disturbed the balance betzueeii ozone
production and destructioii, zuith the result
that ozoiie lez~elsglobally are declining at nn
azwagc' annual ratt, ofO.5%,.As ozoiie lez~els
decreasi,, so fhe lei~td uf UV increases and
U J i f h it the illcidence Of aSS[Jcifltt?d health
prubleiiis. UV causes skin cancers, eye problems, reiluced iinniunity to infectious diseases arid p#SSibly other cancers. Nezu Zealarid
relies 011 pastoral based aizimal production
sysfeinsfiira large part ofits export earnings
arid these ariinials are likely to be affected by
increased UV lez~els.There are few baseline
data u r ~ o i iuhich to judge whether the incidence of skin cancers and irfectious diseases
are increasing, but ezlidencefrom other couiifries, inostly relating to humans, suggests
that it probably is. I f strategies are not dezleloped to ainelioratr the damaging effects of
UV, our animals udl face increased pain and
suffrrin<y\..This rnay impact on Nezu Zealand's a p i d t u r a l trade directly, or indirectly via consuini'r pressure.
The role of ozone
Ozone, a trace gas in the earths atmosphere, plays a critical role in shielding the earth's surface from the lethal
effects of UV radiation from the sun'').
This radiation, which has wavelengths
from 200-400 nm, is called UVC (200-280
nm), UVB (280-320 nm) and UVA (320400 nm)(2).
Ozone strongly absorbs radiation of wavelengths 200-300 nm, absorbing most of the UVB and almost totally
absorbing the UVC, which is lethal to
unicellular organisms and the surface
cells of higher plants and animals. However, it is the small amount of UVB (less
than 1% of the total radiation actually
reaching the surface of the earth)'?)that
potentially has a profound effect on life.
While several factors influence the concentration of ozone at any location, ozone
levels worldwide are steadily declining
at the rate of about 0.5% per year('"*).
As a result of concern over ozone
depletion and the consequent increases
in UVB the Montreal Protocol was developed and signed by a number of nations,
mostly from the industrialised west. The
protocol aims to limit the production of
the man-made materials that are destroying the ozone layer(?).
Factors causing variations in ozone
and UVB concentrations: The earths atmosphere has a series of layers (defined
vertically by temperature changes), the
thickness of which varies with geographical locationand season. The troposphere,
the innermost layer in which we live,
extends upwards to between 16 km over
the equator and 10 km above the poles. In
this relatively unstable sphere the air temperature declines with increasing height.
Above the troposphere lies the stratosphere, extending up to 50 km above the
earths surface, in which air temperature
increases with height because of the absorption of solar radiation by ozone. This
sphere is relatively stable because of the
increasing temperature profile.
Ozone is produced in the atmosphere
by photodissociation of molecular oxygen, primarily in the tropical stratosphere
where UV from solar radiation is most
intense. The rate of synthesis and destruction of ozone is in equilibrium so
that removal of ozone by stratospheric
transport is compensated for by more
ozone being produced. While ozone is
distributed throughout the atmospheric
column, inboth the troposphere and stratosphere, it is long lived only in the stratosphere. Within the troposphere concentrations of ozone are 100 times lower.
Most ozone is produced in the tropical
latitudes and is transported towards the
temperate latitudes. Ozone concentration
at any particular point can vary depending upon a number of factors, which include:
Time of day - there can be a 15%
variation in concentration during the
day as ozone rich or ozone poor winds
sweep across the country.
Season - ozone concentrations arelowest in late summer and highest in late
winter.
Geographical location - in general
there is a natural gradient of increasing ozone with increasing latitude.
The quasi-biennial oscillation - a 26
month stratospheric wind pattern that
influences local ozone concentrations.
The sunspot cycle - as the 11year cycle
reaches its peak solar intensity, the
rate of decline of ozone decreases.
While these factors have a direct impact on the local level of ozone and hence
UVB, other factors can impact on UVB
directly(3)("'.These include:
Cloud c,bver can reduce incident UVB
by up to 50%, although the level of
UVB reaching shaded areas may increase from the scattering effect of the
cloud(').
Water, ice and snow increase the reflection and effectively increase the
amount of incident UVB.
Geographical locationinfluences UVB
by its effect on light path length. The
shorter the path length through the
earths atmosphere the less UVB will
be absorbed by ozone, thus at high
altitudes UVB intensities are higher
than at low altitudes. In winter, when
the sun is lower in the sky, the effective path length is longer and so the
UVB intensity is reduced. Because the
earths orbit is elliptical it is closer to
the sun in the southern hemisphere
summer and the intensity of the incoming solar radiation is higher. As a
consequence the biologically damag-
ing UVB intensity is 10-15% greater
than at the same latitude in the northern hemisphere sumnier when the
earth is at its most distant point from
the sun.
Atmospheric turbidity also increases
path length and can cause a reduction
in UVB. This occurs in the tropics and
the northern hemisphere but not to
any great extent over New Zealand.
While attention has focused on the
ozone in the stratosphere it is the total
column ozone that influences absorption
of UV radiation(').Levels of troposphere
ozone over Europe have increased during the last few years and this has offset
to some extent the decline in stratospheric ozone(').
New Zealand is unique in that, because of its clear sky (relatively low cloud
cover and lack of turbidity) and the closeness of the sun in its southern summer,
the levels of UVB reaching the earth's
surface are higher than at the same latitudes in the northern hemisphere'"'. Evidence points to a continuing decline in
ozone well into the next century. The
issues therefore are both short and long
term and could have profound implications for animals and people in New
Zealand.
Ozone depletion
Anthropogenic emissions of chlorofluorocarbons (CFCs) and their breakdown in the stratosphere to chlorine and
fluorine radicals results in the destruction of ozone molecules('). Because the
stratosphere is relatively stable to vertical motion, once a chlorine or fluorine
radical reaches the ozone layer it may
take u p to 3 years before it is removed by
downward mixing. In this time each radical can cause the destruction of 100,000
ozone molecules.
The CFCs arise solely as a consequence
of human activities. They are chemically
inert until they reach the stratosphere,
and have an estimated lifetime of between 45 and 70 years. Thus their impact
on stratospheric ozone will continue for
many tens if not hundreds of years. It has
been predicted that if all CFC production
were held to 1988 levels, it would take
more than 100 years for ozone levels to
recover to 1988 levels"). As this is unlikely, in spite of the Montreal Protocol, it
would be prudent to assume that ozone
levels will continue to decline and, as a
consequence, UV levels will continue to
increase.
Effects of UV radiation
Much of the study on UV radiation
has focused on human health, using animal models. There is now unequivocal
evidence that UVB has damaging effects
Surveillance23(4) 1996 17
upon skin, eyes and the immune system,
both in cancer development and in ability to withstand infectious diseases("(y!('"!(11)('2).
The effects on skin are cumulative, related to both the duration
and intensity of exposure to solar radiation. Although the relationships are complex there is a strong association between
exposure to sunlight (and UVB) at an
early age and the later development of
malignant and non-malignant carcinoma in humans""). The same may be true
for animals. The eyes can develop various forms of keratitis as a result of exposure to UV radiation'l2].
The effects of UVB on the immune
system and the development of infectious diseases is potentially even more
damaging and considerably less well
documented or understood. UVB is of
the same wavelength as the absorption
spectrum of deoxyribonucleicacid (DNA)
(290-320nrn)'"), the fundamental instruction code for normal cell growth, development and function. If DNA is damaged it can affect the cell's ability to function normally. UVB can cause breaks or
lesions in the DNA structure and these
may or may not be repaired. In cells of the
immune system this damage can lead to
altered immunity via reduced immunosurveillance, lowered detection and response to invading foreign bodies and
reduced antibody response'l*).Studies in
mice have shown that if a normal mouse
is implanted with a UVB induced tumour from another mouse, the tumour
usually regresses. However, if the recipient mouse has been irradia ted with UVB,
the implanted tumour usually develops(11'.
There is little systematic evidence of
the effects of UVB on animal life, and the
incidence of UVB related disea~es''~'.
Within New Zealand there are few data
to indicate the likely effects of additional
UVB arising from ozone depletion on
animal health and welfare(l4!'.The need
for systematicmonitoring of farm animal
diseases using existing veterinary and
government inspection services has been
raised(*!as part of a strategy to gather
further information necessary to judge
the effects of increasing levels of UVB on
animal health and welfare.
Diseases in farm animals
associated with exposure to
sunlight and UV
Following are some examples of animal diseases attributed to sunlight or
more particularly UVB. They may beuseful as indicators of various welfare problems and may suggest some possible strategies to cope with the predicted increase
in UVB levels in New Zealand.
Cancer eye in Hereford cattle: Studies
in the USA("' indicated that those cattle
lacking pigment around the eye are most
susceptible. The incidence was as high as
21% in some herds, and was also related
to latitude and to animal age; older animals having a higher incidence. It has
been suggested that selecting for pigmented skin would be ineffectivebecause
18 Surveillance 23(4) 1996
the rate of change inUVB intensity would
be too rapid for any breeding programme
to be successful"").
Papillomatosis ingoats: This disease
is exacerbated by non-pigmented skin,
UVB and reduction in host defences. It
occurs most frequently in adult goats,
with development of warts on the unpigmented areas of the udder and around
the eyes. It has been most frequently
observed in regions of high sunlight, such
as Australia, India, Iraq and South Africa. It reinforces the evidence that pigmented skin offers some protection to
animals from the harmful effects of
UVB("1.
Sunburn in sheep: An Australian
study("! showed that chemically denuded sheep can suffer severe sunburn and
thatthiswouldbelikelyforup to9 months
of the year if chemical defleecing was
practised in the major wool growing regions of that country. The study confirmed that pigmented skin had a protective effect as sheep with pigmented skins
(Suffolk) required up to four times the
dose of radiation to develop sunburn as
did the Merino sheep. As it has been
suggested that the incidence of sunburn
in dairy cows in New Zealand is increasing(*),the provision of shelter and the
timing of husbandry procedures such as
shearing need consideration.
Studies have shown that certain plants
are able to develop chemicals to combat
the effects of UVB'l9)',but if consumed by
livestock these may cause photosensitisation or result in the development of
phototoxins.
Possible outcomes of increased
UVB and implications for animal
health and welfare
The seasonal variation in both ozone
and consequent UVB levels mean it is
likely that there will be an increase in the
incidence of some infectious diseases
through summer, when ozone levels are
up to 40% lower than in winter.
It is likely that there will be an increase in skin cancers in the animal population as this is related to total exposure,
but also that younger animals will also be
affected as the rate of accumulation of
damaging UVB is itself increasing. There
is also conjecture that for various forms
of life there may be a UVB threshold, as
yet undefined but which may now be
being rapidly approached. Changes in
UVB intensity can be more damaging to
life at frequencies nearer 300 nm than 310
nm, because of the biological response
curve to changes in radiation wavelength"').
While skin cancers, cancer eye and
infectious disease will continue to be treated in the short term by conventional veterinary procedures this does not address
the issues of animal welfare or trade barriers. In attempting to combat health problems the pastoral industries may become
more rather than less reliant on drugs.
Animal welfare in our farmed flocks may
become progressively reduced through
pain and discomfort, from easily detect-
ed conditions such as cancer eye but also
from less obvious chronic infectious diseases, which may be reflected in reduced
fertility, reduced growth and higher levels of mortality to disease'"'.
Within New Zealand the beef cattle
population is based primarily upon a
mix of Hereford and Aberdeen Angus
within which there is a large degree of
variability in pigmentation of the skin,
particularly around the eyes. From a
welfare perspective it would be sensible
to breed replacements only from cattle
with the required pigmentation.
The anecdotal evidence from veterinary practitioners in New Zealand(') that
sunburn in dairy cattle is becoming more
common may indicate that it is occurring
more commonly in all farm animals but
is only being seenindairy animals, which
are handled more frequently. Without
accurate information it is not possible to
determine how much the incidence is
changing, but it does raise the questionof
shelter, animal behaviour and minimum
care strategies of farming in New Zealand. There is a need to understand animal behaviour such as shade seeking at
different times of the day. It may be necessary to provide shade where there is
none at present and possibly also actively encourage animals to seek shade during the high risk time of day@).
There is presently no adequate record
in New Zealand of the incidence of infectious diseases in farm animals that could
be attributable toUVB. Theevidence suggests that animals' immune systems will
be damaged by increasing levels of UVB,
therefore it would be prudent to develop
strategies now for coping with the expected change, in both disease prevention, control and treatment, and in animal husbandry practices for such things
as shearing, providing shelter, pasture
species as food and modifying animal
behaviour in relation to incident UVB.
References
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(2)
(3)
(4)
(5)
(6)
(7)
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Ozone Depletion: Health and Environmental
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McKenzie RL. UVB and its global variability. The Royal Society of New Zealand, Miscellaneous Series 25, 3-4, 1993.
Matthews WA, Keep DJ. Ozone trends and
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L B Mutthews and B W Hogg
Animal Behaviour and Welfare Research Centre
AgResearch Ruakura
Private Bag 3 123
Hamilton
Emai1:inatthewsl @agresearch.cri.nz
Surveillance 23(4) 7 996 19