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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 (1) (2) (3) (4) (5) (6) (7) Watson TR. Present state of knowledge ofthe ozone layer. In: Jones RRT, Wigley T (eds). Ozone Depletion: Health and Environmental Consequences. Pp 43-58. John Wiley and Sons Ltd West Sussex, England, 1989. McManus N. No ozone no godzone. A preliminary study ofthe impacts of ultraviolet (UV) radiation on New Zealand. Greenpeace New Zealand, 1993. 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 variability, globally and over New Zealand. The Royal Society of New Zealand, Miscellaneous Series 25, 2-3,1993. Uuher P. The Montreal Protocol on substance5 that deplete the ozone layer: its development and likely impact. In: Jones RRT, Wigley T (eds). Ozone Depletion: Health and Environmental Consequences. Pp 1 15- 140. John Wiley and Sons Ltd West Sussex, England, 1989. McKenzie RL, Elwood JM. Intensity of solar ultraviolet radiation and its implications for skin cancer. New Zealand Medical Journal 103, 1.52-4,1990. Miins FM. Beware the glare of black light. New Scientist 1957, 71-2,1994. (8) Elwood, JM. Assessmentofthe human health impact of changes in ultraviolet levels. The Royal Society of New Zealand, Miscellaneo u \ Series 25, 12-3,1993. (9) Arlett CF, Cole J. Photosensitive huinan syndroines and cellular defects in DNA repair. In: Jones RRT, Wigley T (eds). Ozone Depletion: Health and Environmental Conaequences. Pp 147-160. John Wiley and Sons Ltd West Sussex, England, 1989. (IO) Armstrong BK, de Klerk NH, Holinan CDJ. Etiology of cominon acquired inelanocytic nevi: Constitutional variables, uun exposure, and diet. Journal of the Cancer Institute, 77, 329-35. 1986. ( 1 1 ) Van Der Leun JC. Experimental photocarcinogenesia. In: Jones RRT, Wigley T ieds). Ozone Depletion: Health and Environmental Consequences. Pp 1 h 1-89, John Wiley and Son\ Ltd West Su\sex, England, 1989. ( 1 2) Jones RR. Consequences for human health of stratospheric ozone depletion. In: Jones RRT, Wigley T (eds). Ozone Depletion: Health and Environmental Consequences. Pp 207-27. John Wiley and Sons Ltd West Sussex, England, 1989. ( I 3) Worrest RC, Grant LD. Effects of ultravioletB radiation on terrestrial plants and marine organisms. In: Jones RRT, Wigley T (eds). Ozone Depletion: Health and Environmental Consequences. Pp 197-206. John Wiley and Sons Ltd West Sussex, England, 1989. (14) Stockdale PHG. Ultraviolet radiation: effects on animals. The Royal Society of New Zealand, Miscellaneous Series 25, 20-1,1993. (15) Anderson ED, Badzioch M. Association between solar radiation and ocular squamous cell carcinoma. American Journal of Veterinary Research, 52, 784-8, 1991. (16) Mayer SJ. Stratospheric ozone depletion and animal health. Veterinary Record 131, 120.2, 1992. (17) Theilen G, Wheeldon EB, East N, Madewell B, Lancaster WD, Munn R. Goat papillomatosis. American Journal of Veterinary Research 46, 2519-26, 1985. ( 18) Chapman RE, Bennett JW, Carter NB. Erythemal responses of biologically denuded sheep to sunlight and the effects on skin structure and wool growth. Australian Journal of Biological Science, 37, 217-35, 1984. (19) Laing W. UVB radiation and New Zealand agriculture. The Royal Society of New Zealand, Miscellaneous Series 25, l6-7,1993. 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