X-Rays are high-energy radiation capable of passing through considerable thicknesses of many substances which are opaque to ordinary light, without undergoing material absorption, but other substances, even in very small thick- nesses, are able to absorb the great majority of the rays: thus, flesh is very transparent; healthy bone is fairly opaque. Widely used for diagnos- tic imaging of internal body structures and (in human medicine) for radiotherapy. Precautions Guard screens of lead glass, rub- ber impregnated with lead, or sheet lead, are used to protect the operators of radiographic apparatus, and precautions are necessary to shield the testes and ovaries of young persons and animals from the sterilising effects of the rays. Detailed precautions are as follows: 1. Persons under 16 years must not take part in radiological procedures. 2. Fluoroscopy (imaging) or radiotherapy should not be carried out except under expert radiological guidance. Hand-held fluoroscopes must not be used in any circumstances. 3. Personnel radiation monitoring devices, such as film badges, must be worn by all per- sons who take part routinely in radiological procedures. 4. The animal should, if possible, be anaes- thetised or tranquillised for radiography, and all persons should withdraw as far as practicable from the useful beam. 5. If it should be necessary to hold the ani- mal for radiography, lead-protective gloves and aprons must be worn. Whenever possible, hold- ing should be done by the owners, unless they are under 16 years or pregnant. 6. Persons should not expose any part of their bodies to the useful beam even when wearing protective clothing. 7. The useful beam should be restricted to the area being examined by means of a beam- limiting device. Notes on protection against radiation will also be found in the British Veterinary Association’s guide to the Health and Safety at Work Act. Regulations In the UK, the Ionising Regulations 1985 require veterinary surgeons using X-ray equipment to notify their local Health and Safety Executive. Many veterinary practices now employ a radiation protection adviser to ensure compliance with the require- ments of the regulations. Radiography The production of a radi- ograph of the internal structure of a small ani- mal is a comparatively simple matter once the difficulty of control is overcome. The animal is arranged upon the table in such a position as to allow the rays to pass down through the part and become registered upon a sensitive plate placed flat upon the table immediately below. The animal may lie upon its back, on one or the other side, or on its chest and abdomen with the legs pulled out from under it. To maintain this position it is always advisable to administer an anaesthetic. The discharge tube is best arranged immediately above the animal in such a position as to allow the rays to fall perpendic- ularly down through the body on to the plate. (For screening, the tube must be below the table, and the screen held or supported above the animal.) The period of exposure to the pas- sage of the rays varies according to the tissues, to the type and power of the equipment, to the distance of the tube from the plate, and to whether or not an intensifying screen is used. There are many conditions in which the actual extent of injury or disease can be accu- rately discovered by the use of X-rays, but the most important are diseases and injuries of bones. Fractures of the limb-bones are well shown, and their extent is better realised than is possible by palpation. Exostoses (overgrowths of bone) can also be clearly indicated, while tumour formation (usually sarcomatous) shows as a thinning and enlargement of the bone tissue. Where only one limb is affected it is advisable to arrange the animal so as to include a picture of the normal limb for comparison. Foreign bodies – especially needles, pins, nails, and other metallic substances – which have been swallowed are best shown by a profile view of the abdomen. Pieces of game bones (which are specially dense and show up well) can also be seen in the stomach or intestines, and are very often surrounded by gas, which, in the negative, appears as a dark shadow – the bone itself appearing light. Internal tumours can very often be diagnosed. They appear as more or less discrete pale areas in positions where a radi- ograph from a normal animal is denser under the same conditions of exposure, etc. Certain tumours can be made to show up well by giving the animal medicinal doses of a lead salt for a few days before taking the plate. Some of the X lead becomes deposited in the tumour and intensifies the contrast. Where some displace- ment, stricture, or dilatation of the stomach or of part of the intestinal canal is suspected, the animal is given a feed or a draught containing an emulsion of bismuth or barium carbonate, or some other harmless metallic salt, or has some of the same material injected into the rec- tum. After waiting until the salt has become suitably distributed, a radiograph of the Xanthosis 785 X A teaspoon in the stomach of a cocker spaniel. The spoon was swallowed while the animal was being given cod-liver oil. (Reproduced by courtesy of Mr S. W. Douglas, University of Cambridge School of Veterinary Medicine.) Radiography reveals that a painful swelling on the leg of a St Bernard is due to an osteosarcoma involving the radius. (Reproduced by courtesy of Mr S. W. Douglas, University of Cambridge School of Veterinary Medicine.) X 786 Xanthosis abdomen is taken, and the outlines of those organs to which the salt has been carried by peristalsis, can be made out as pale areas in the negatives. Other conditions in which X-rays are useful are as follows: stones in the kidney, urinary or gall-bladder; dilatation of the heart; solidifica- tion of a portion of a lung; and pleurisy. Portable X-ray apparatus is available for use in, for example, examining the lower limbs of a horse at the stable. Computed tomography A sophisticated and effective method of visualising the interior of the body, this has revolutionised radiography. A focused electronic imaging scanner is used to build up, by a series of consecutive exposures, a picture of an organ or specific area. The result- ing image is enhanced by computer analysis and viewed on a visual display unit (VDU) which shows a clear picture without the the superimposition of other body tissues which surround the targeted area. In the apparatus, whose British development was by Godfrey Hounsfield FRS, crystal detectors are used in place of the film in a normal X-ray system. Radiotherapy X-ray therapy has been applied to a limited extent in the treatment of certain tumours in the dog. Xanthosis Xanthosis is a yellowish-brown pigmentation of meat, generally affecting the heart and the tongue. It gives the meat an objectionable colour, but is quite harmless. Xenophthalmia Inflammation of the eye caused by a foreign body. Xerophthalmia A disease of the eye associated with a vitamin A deficiency. There is thickening and cloudiness of the conjunctiva and cornea; blindness may result. Xylazine A sedative used to render animals easier to han- dle, it is widely used in dogs, cats, horses, farm livestock, and zoo animals. It is also used for pre-anaesthetic medication and for general anaesthesia in combination with ketamine. Xylazine increases blood glucose levels and urine output. Side-effects may include brady- cardia, slower breathing, and lowered blood pressure. In cattle tolazoline has been used as a xylazine antagonist. Yarded Cattle Before yarding cattle in the autumn, it is wise to make a gradual change from sugar-poor autumn pasture to things like roots; otherwise digestive upsets are likely to occur. Similarly, in spring it is a mistake to turn calves straight out on to grass. This means a sudden change from protein-poor food to the rich protein of the early bite, and the resulting effect upon the rumen will set them back. It is best to get them out before there is much grass for a few hours each day; let them have hay and shelter at night to protect them from sudden changes of weather. Hypomagnesaemia, too, is far less likely under these circumstances. ( See also HOUSING OF ANIMALS .) Boss cows can be a nuisance in yards, but the provision of yokes for feeding overcomes the main diffculty. When self-feeding of silage is practised, pre- cautions are necessary in order to prevent foot troubles. ( See SILAGE .) Yarded animals fed on cereals, sugarbeet pulp, straw, and hay – but with little or no greenstuff – may suffer from xerophthalmia and go blind as a result of a vitamin A deficiency. Yawning Yawning is an important sign of KIMBERLEY HORSE DISEASE ; it may also be seen in cases of LABURNUM POISONING and NARCOLEPSY . Yeast Yeast is a valuable source of vitamin B, but should not be fed in excessive amounts to pigs or it may give rise to rickets unless adequate vit- amin D is simultaneously available. Yeast has proved successful in the treatment of tropical ulcers in humans, and success has been report- ed in a limited number of cases in horses in the tropics. The human patients were mostly those whose diet was deficient in vitamin B, a defi- ciency further increased by sweating. The yeast was applied directly to the ulcer, and a small quantity given internally also. Yeasts Yeasts sometimes cause enteritis, and are impor- tant in some cases of refractory otitis in the dog. ( See FUNGAL DISEASES.) Yellow Fat Disease of Cats (see STEATITIS ) Yellow Fever A viral disease affecting man and other verte- brates, principally monkeys, in large areas of tropical America and Africa. There are 2 known cycles of transmission, the urban and jungle cycles. In the urban cycle, man is the reservoir and Aedes aegypti probably the only vector. This cycle from man to A. aegypti to man is now virtually unknown in the Americas owing to efforts to eradicate the vector, but it is still common in Africa. The jungle cycle has a primate reservoir maintained by various mosquitoes. Movement of virus from the monkey-mosquito-monkey cycle into man is accidental, and is the result of human penetration into jungle where the disease is endemic. The causative organism is classified as a flavivirus. Yelt A female pig intended for breeding, up to the time that she has her 1st litter. Yersiniosis Infection with Yersinia pseudotuberculosis or with Y. enterocolitica. Up to 1960, states WHO, only the former organism was regularly isolated in man and animals in Europe; but since then most of the isolations have been of Y. enterocolitica. ‘Pseudotuberculosls’ in the early 1990s was still occasionally found in rodents and birds, especially in France and the UK, and is a zoonosis. People may become infected through pets such as guinea pigs, hamsters, and cats, all of which may have a subclinical infection only but excrete Y. pseudotuberculosis. An investigation in Invermay, New Zealand, resulted in Y. pseudotuberculosis being isolated from 675 apparently healthy small mammals and birds. In descending order of prevalence were feral cats (27.8 per cent), Norway rats (8.6 per cent), mice, hares, rabbits, ducks, sparrows, seagulls and starlings. In New Zealand, yersiniosis has also emerged as a serious disease of farmed red deer. It appears to be triggered off by stress, and most cases occur during the winter. Cats (which are liable to become infected by their prey) may also show clinical symptoms: loss of appetite, vomiting and diarrhoea. Also loss of weight. Y Pheasants Yersiniosis is an important cause of death of these birds in the UK. Yersinia enterocolitica infection in Europe was first found in hares, in outbreaks of disease on chinchilla farms, in monkeys in zoos, and in guinea pigs. There may be enteritis and other lesions, but symptomless carriers have been found among all the farmyard mammals and birds. Occasionally Y. enterocolitica has been isolat- ed from cases of mastitis in cows, endocarditis in bulls, and septicaemia in pigs. In cattle, the antibody produced may be difficult to differen- tiate from that produced by Brucella abortus. Camels, foxes, and fleas may also carry the organism. Public health Yersinia enterocolitica infection is not regarded as a genuine zoonosis by WHO. Person-to-person infection occurs, and also infection from soil-contaminated vegetables. The human illness is characterised by enteritis, and is a cause of diarrhoea, although less impor- tant than salmonella and campylobacter. Ileitis may be accompanied by acute pain, suggestive of appendicitis. A mesenteric adenitis is also seen, and sometimes polyarthritis, deep abscesses, eye lesions, and occasionally septicaemia. In the UK in 1984, 250 cases were reported. Outbreaks in North America have been linked to raw milk. (For Y. pestis see BUBONIC PLAGUE , which can occur in cats and dogs in subclinical form.) Yew Poisoning All varieties of the British yew trees are poiso- nous, but owing to its more frequent cultiva- tion, the common yew (Taxus baccata) is most often responsible for outbreaks of poisoning among animals. The Irish yew (T. baccata var. fastigiata) and the yellow yew appear to contain less of the poisonous alkaloid, which is called taxine. The bark, leaves and seeds all contain it. The older dark leaves are more dangerous than the fresh green young shoots, which cattle have been known to eat in small amounts without harm. Cases of poisoning have been noted among horses, donkeys, mules, cattle, sheep, goats, pigs, deer, rabbits, and even pheasants, but the majority of cases occur in young store cattle and in dairy cows which have access to the shrubberies, graveyards, etc., where yew trees are most common. Signs In many cases cattle drop dead without showing any preliminary symptoms at all. They may fall while cudding almost as suddenly as if shot. In other cases where less has been eaten, excitement and paresis may be seen. Treatment Antidotes are as for alkaloids. If time allows, rumenotomy may be carried out. Yolk Sac Infection (see OMPHALITIS OF BIRDS ) Yorkshire Terrier A long-haired, black-and-tan coloured toy dog. The breed is prone to tracheal collapse caused by a cartilage defect that may or may not be inherited. Patellar luxation is inherited as a recessive trait. Yorkshire Boarding Vertically arranged boards with a gap between each, used for partial cladding of a livestock building. It is a very useful means of improving ventilation and avoiding condensation, thereby reducing the risk or incidence of bronchitis and pneumonia in housed livestock. 788 Yew Poisoning Y Zearalenone An oestrogenic toxin from the fungus Fusarium graminearum of standing corn. The toxin has caused abortion in sows, and possibly a splayleg condition in piglets. Zebu Bos indicus, the cattle of India, East and West Africa, and Southeast Asia. The American name is Brahman; in South Africa, the Afrikaner. Zero-Grazing Taking cut fodder to yarded cattle, or to cattle in exercise paddocks. Zero-grazing has a place on heavy land, with high stocking rates and large herds. It obviates poaching and the spoil- ing of grass, and a given acreage zero-grazed can provide more grass than if grazed. It means, however, cutting grass every day, and mechani- cal failures can upset the system. It is not yet considered economic for sheep. Zinc (Zn) Zinc (Zn) is a trace element, and a deficiency has occurred in pigs. ( See PARAKERATOSIS.) A zinc supplement to prevent or correct this con- dition must be used with care, as 1000 parts per million can cause poisoning. It seems that a high calcium intake by pigs aggravates a zinc deficiency. A zinc deficiency may also occur in dogs, especially in those fed largely on flaked maize or ‘loose cereal-based diets’. Signs include a predis- position to skin infections, a poor coat, localised alopecia, and hardening of the skin in places. Response to a zinc supplement is usual- ly quick. ( See SHEEPDOGS.) A zinc supplement has been used to protect sheep against facial eczema due to ingestion of the mycotoxin sporidesmin. External uses Zinc oxide is an ingredient of ointments; the carbonate an ingredient of calamine lotion used for moist eczema, etc. The sulphate in weak solution has been used in wound treatment and in eye lotions; the chloride – a caustic – to repress granulations. Zinc Bacitracin An antbiotic formerly used as a feed additive to improve growth rate in most farm animals and egg production in poultry. ( See ADDITIVES.) Zinc Poisoning Chronic zinc poisoning has been reported in a dairy herd as a result of contaminated drinking water – caused by interaction between copper pipes and newly galvanised tanks. The main symptom was chronic constipation throughout the herd, and a diminished yield from the cows in milk. Fatal zinc poisoning has occurred in dairy cattle fed on dairy nuts to which zinc oxide has been added instead of magnesium oxide. The first death occurred after 3 weeks. Zinc-responsive skin disease The most common cause of this is the feeding of soya or cereal-based diets – with little or no meat, which is rich in zinc. Some dogs may have an inherent defect which limits zinc absorption. Signs A dull, harsh coat; sometimes with whitish crusts on the skin. Zondek-Ascheim Test (see PREGNANCY DIAGNOSIS ) Zoo Licensing Act 1981 The Zoo Licensing Act 1981 is intended to pro- mote animal welfare and public safety at zoos. It covers any collection of wild animals (including mammals, birds, reptiles, fish, and insects) in Britain to which the public has access for more than 7 days in any 12-month period; but exempts pet shops and circuses, as these are cov- ered by the Pet Animals Act 1951 and the Performing Animals (Registration) Act 1952. Of 150 zoos inspected following the passing of the Act, only 5 were refused a licence; and in those cases it was public-safety considerations rather than the quality of animal care which brought about the refusal. Zoonoses Diseases communicable between animals and man. Information about them will be found under the following headings: ARIZONA INFEC- TION ; BABESIA – Babesiosis; ANTHRAX; B VIRUS (from monkeys); BRUCELLOSIS; CAT-SCRATCH FEVER ; CHAGAS DISEASE; EQUINE ENCEPHALITIS; EQUINE INFECTIOUS ANAEMIA; FOOT-AND- MOUTH DISEASE (very rare in human beings); GLANDERS; HYDATID DISEASE; LEPTOSPIROSIS; LISTERIOSIS; LIVER-FLUKES; LOUPING-ILL; LYME DISEASE ; LYMPHOCYTIC CHORIOMENINGITIS (from mice); NEWCASTLE DISEASE; ORNITHOSIS; ORF; PASTEURELLOSIS; Q FEVER; RABIES; RATBITE FEVER ; RIFT VALLEY FEVER; RINGWORM; ROCKY MOUNTAIN FEVER ; RUSSIAN SPRING-SUMMER VIRUS ; SALMONELLOSIS; SCABIES; SCHISTOSOMI- Z ASIS; TAPEWORMS;TICK-BITE FEVER; TICK PARAL- YSIS ;TOXOCARA;TOXOPLASMOSIS;TRICHINOSIS; TUBERCULOSIS ; TULARAEMIA; VESICULAR STOM- ATITIS ; MARBURG DISEASE; WESSELBRON DIS- EASE ; YERSINIOSIS; YELLOW FEVER; SWINE VESIC- ULAR DISEASE ; PORCINE STREPTOCOCCAL MENINGITIS ; ROTAVIRUS ; LASSA FEVER ; BOVINE ENCEPHALOMYELITIS; LEISHMANIASIS; BUBONIC PLAGUE ; ENCEPHALOMYOCARDITIS.) It should be added that typhus and plague may be transmitted, by flea-bite, from rats; and, in jungle areas, yellow fever, by mosquito- bite, from monkeys. ( See also under RODENTS ; MONKEYS; INFLUENZA .) Among skin diseases, the parasite of follicu- lar mange may occasionally infest the human eyelid. Among eye infections, INFECTIOUS BOVINE KERATOCONJUNCTIVITIS should be mentioned. Human enteritis has followed con- tact with sheep affected with campylobacter abortion. ( See also BIRD-FANCIER’S LUNG ; MELIOIDOSIS; CAMPYLOBACTER INFECTIONS; CHLAMYDIA; PSITTACOSIS; BOUTONNEUSE FEVER; LEISHMA- NIA ; HANTAVIRUS ; TICK-BORNE ENCEPHALITIS; EHRLICHIA CANIS; ABORTION, ENZOOTIC.) Zoonoses in UK Veterinarians A questionnaire was distributed to 1717 mem- bers of veterinary and support staff of the Ministry of Agriculture and the Institute for Research on Animal Diseases; 1625 (95 per cent) responded, comprising 563 veterinary surgeons, 690 scientific staff and 372 technical support staff. A total of 1057 (61.5 per cent) had apparently not suffered any zoonotic infec- tion. Animal ringworm was the commonest reported zoonosis. The incidences of ringworm, brucellosis and Newcastle disease were higher in the veterinary and support staff than in the laboratory workers. In contrast, ornithosis, salmonellosis and Q fever occurred at least as often in the laboratory staff. Fourteen people developed tuberculosis during their employ- ment, although only 1 was caused by Mycobacterium bovis. The veterinarians report- ed 441 injuries that resulted from accidents at work; 397 (71 per cent) of these involved ani- mal-handling. The comparable figures for labo- ratory workers and technical staff were 329 and 103 (15 per cent) and 198 and 179 (42 per cent) respectively. Zoonoses Orders 1988 & 1989 These include measures intended to reduce the risk to humans of salmonella and brucella infections of animal origin. The 1989 Order recognises bovine spongiform encephalopathy as a zoonotic disease. Zootechny Animal management. Zygoma Zygoma is the bridge of bone which runs from near the base of the ear to the lower posterior part of the eye-socket. It protects the side of the bony orbit, forms part of the support of the outside of the joint of the lower jaw with the rest of the head, and serves as a base of attach- ment for part of the strong masseter muscle which closes the mouth and is important in the chewing of the food. The zygomatic arch (another name for the zygoma) is formed by projections from the temporal, zygomatic, and maxillary bones. Zygote The body that results from the fertilisation of an egg cell by a sperm. 790 Zoonoses in UK Veterinarians Z Animal Health Trust PO Box 5, Newmarket, Suffolk CB8 8JH. 01638 750659 Association of Pet Behaviour Counsellors PO Box 46, Worcester WR8 9YS. 01386 751151 Association of Pet Dog Trainers Peacock’s Farm, Northchapel, Petworth, West Sussex GU28 9JB Blue Cross 1 Hugh Street, London SW1V 1QQ. 020 7834 1128 British Cattle Movement Service Curwen Road, Workington, Cumbria CA14 2DD. 0845 0501234 British Cattle Veterinary Association The Green, Frampton-on-Severn, Gloucestershire GL2 7ER. 01452 740816 British Equine Veterinary Association 5 Finlay Street, London SW6 6HE. 020 7610 6080 British Horse Society British Equestrian Centre, Stoneleigh Deer Park, Kenilworth, Warwickshire CV8 2LR. 08701 220224 British Rabbit Council Purefoy House, 7 Kirkgate, Newark, Nottingham NG24 1AD. 01636 676042 British Veterinary Association 7 Mansfield Street, London W1G 9NQ. 020 7636 3541 Companion Animal Welfare Council 43 Brook Field Lane, Harlow, Essex CM18 7AU DARD (Department of Agriculture and Rural Development) Dundonald House, Upper Newtownards Road, Belfast BT4 3SB. 028 9052 4580 DEFRA (Department of the Environment, Food and Rural Affairs) 1A Page Street, London SW1P 4PQ Donkey Sanctuary Sidmouth, Devon EX10 0NU. 01395 578222 Farm Animal Welfare Council DEFRA, 1A Page Street, London SW1P 4PQ Farriers Registration Council Sefton House, Adam Court, Newark Road, Peterborough PE1 5PP. 01733 319911 Kennel Club 1 Clarges Street, London W1Y 8AB. 0870 6066750 National Association of Farriers, Blacksmiths & Agricultural Engineers The Forge, Avenue B, 10th Street, NAC, Stoneleigh, Warwickshire CV8 2LQ. 024 7669 6595 National Canine Defence League 17 Wakely Street, London EC1V 7LT. 020 7837 0006 National Farmers Union Agriculture House, 164 Shaftsbury Avenue, London WC2 National Office of Animal Health 3 Crossfield Chambers, Gladbeck Way, Enfield, Middlesex EN2 7HF National Poisons Information Service Avonley Road, London SE14 5ER. 020 7635 9195 NOAH (National Association of Animal Health) 3 Crossfield Chambers, Gladbeck Way, Enfield, Middlesex EN2 7FH. 020 8367 3131 PDSA (People’s Dispensary for Sick Animals) Whitechapel Way, Priorslee, Telford, Shropshire TF2 9PQ. 01952 204713 Pets Travel Scheme (PETS) Helpline: 0870 41171; fax 020 7904 6834; e-mail pets@ahvg.maff.gov.uk/animalh/quarantine Royal College of Veterinary Surgeons Belgravia House, 62–64 Horseferry Road, London SW1P 2AF. 020 7222 2001 RSPCA (Royal Society for the Prevention of Cruelty to Animals) Causeway, Horsham, West Sussex RH12 1HG. 01403 264181 UFAW (Universities Federation for Animal Welfare) The Old School, Brewhouse Hill, Wheathampstead, Hertfordshire AL4 8AN. 01582 9303611 USEFUL ADDRESSES . SPRING-SUMMER VIRUS ; SALMONELLOSIS; SCABIES; SCHISTOSOMI- Z ASIS; TAPEWORMS;TICK-BITE FEVER; TICK PARAL- YSIS ;TOXOCARA;TOXOPLASMOSIS;TRICHINOSIS; TUBERCULOSIS ; TULARAEMIA; VESICULAR STOM- ATITIS ;. WHO. Person-to-person infection occurs, and also infection from soil-contaminated vegetables. The human illness is characterised by enteritis, and is a cause of diarrhoea, although less impor- tant. ARIZONA INFEC- TION ; BABESIA – Babesiosis; ANTHRAX; B VIRUS (from monkeys); BRUCELLOSIS; CAT-SCRATCH FEVER ; CHAGAS DISEASE; EQUINE ENCEPHALITIS; EQUINE INFECTIOUS ANAEMIA; FOOT-AND- MOUTH DISEASE (very