Deer at low population densities on natural range are generally not affected by disease to any significant extent. However, they are susceptible to many diseases and hence disease becomes an important factor in the intensive management of deer. Deer often die extremely rapidly - in many cases within 24 hours of the onset of clinical signs.
The age and condition of a deer population affects the level of parasitism and disease. Generally speaking, as the number of animals held in captivity increases, so do losses due to diseases, if measures are not taken to prevent them. Deer in their first 12 – 15 months of life are more susceptible to disease than adults.
General information concerning deer diseases can be obtained in Davis, Karstad and Trainer (1970), about parasitism in Wetzel and Rieck (1972), and about veterinary techniques regarding deer farming in McAllum (1977).
Salmonellae have been isolated from some deer species. Yersinia s.c. bacteria which are associated with yersiniosis have only recently been recognized as a major cause of death in farmed deer in New Zealand. Outbreaks were manifested by gastroenteritis and sudden death of deer of all ages, but mainly young deer.
Tuberculosis have been recorded among various deer species; it can become widespread among farmed deer if testing and slaughter of reactors is not conducted.
Clostridial diseases (blackleg, black disease, braxy and pulpy kindey) have been diagnosed in deer. Of these, the latter appears to be the more serious condition in farmed deer. Leptospirosis is infrequent in occurrence among deer. Brucellosis occurs among deer, but at a low frequency, as does Johne's disease, also rather rarely. Footrot and wound infections and abscess formation are not uncommon among fallow deer in West Germany (Ueckermann, 1968).
Deer are subject to various viral diseases.
Malignant catarrhal fever has occurred among cervids in many countries, and has resulted in sporadic or multiple deaths. It has been one of the most serious diseases to occur on deer farms in New Zealand.
Outbreaks of foot and mouth disease have been reported in Europe and the USSR, and as sporadic occurrences elsewhere in many species of deer (Forman and Gibbs, 1974). A haemorrhagic disease similar to bluetongue has occurred in many areas of North America where it has been very destructive among some herds. Deer are susceptible to rinderpest and mortality rates are often high.
Mucosal disease has occurred in white-tailed deer in North America (Richards et al. 1956).
Although rabies occurs among deer, and especially among roe deer, they play an unimportant role in the spread of the disease (Cappuci and Longhurst, 1972). It occurs rather frequently among fallow deer in West Germany (Ueckermann, 1968).
Louping ill is confined to Britain. In a certain area in Scotland 29% of red deer hinds and 44% of stags had antibodies to this disease (Dunn, 1960). It appears that farmed deer are more threatened than wild ones by this disease (Reid et al, 1978)
Healthy deer normally do not have many worms. A low burden probably initiates immunity to the parasite and hence the host resists high burdens where grazing and reinfestation pressures are not too great.
Lungworms occur among most deer on the open range and they are considered to be a serious potential threat to deer farming. Large lungworms (Dictyocaulus) occur in the main bronchi of the lungs. They do not require an intermediate host. Most lungworm infestations are small and have no obvious clinical effects upon the animal, but complications can occur when burdens become heavy, particularly in the young animal. There are widespread reports of gastrointestinal parasitism in deer from many countries of the world. An extensive range of parasites has been identified in the various species of deer. Generally gastrointestinal parasitism is most pronounced in younger animals up to 2 years of age.
Elaphostrongylus cervi is a nematode parasite which has its adult stage located in many tissues throughout the body but, in particular, the central nervous system and intermuscular connective tissue. It occurs in several deer species.
Liverflukes (Fasciola hepatica and Dicrocoelium lanceolatum) are present in many species of deer. High infestation rates of Fasciola have been recorded in red deer in Germany. Fasciola infestations also have been a problem in North America.
Echinococcus cysts have been reported in some deer species, although it appears that deer are poor hosts of this parasite and infestations are rare. The intestinal tapeworms Moniezia benedeni and M. expansa occur among deer.
The following Protozoa are found in deer:
Coccidia: A wide range of coccidia species occur in deer throughout the world. Coccidiosis does not appear to pose a major threat to farmed deer.
Toxoplasmosis: Antibodies of Toxoplasma gondii have been found in deer blood on many occasions.
Sarcosporidiosis: Numerous reports of sarcosporidiosis are recorded in the literature. Infection rates of up to 15% have been reported in some red deer herds.
Babesiasis: Many species of deer carry the known vectors of Babesia. There are no reports of clinical symptoms in deer caused by Babesia species.
Ectoparasites are more of a threat to farmed deer than to wild ones, because in general, higher stocking rates are apt to result in higher parasite incidence.
Lice occur frequently on farmed deer. Lice could affect young animals and deer in poor conditions during winter, but so far no serious problems have been experienced. Ticks are often found on deer. Among the many species, Ixodes ricinus is most commonly recorded.
Keds (Lipoptena Cervi) have been observed on farmed deer in Scotland (Blaxter et al, 1974).
Mite (Demodex) species have been described from deer, but their importance is not yet known.
Warble flies may frequent deer in the wild to such and extent that hides can be rendered useless for leather production. Only in New Zealand, where warble flies do not occur, are skins not damaged. The throat warble fly, which occurs among red and roe deer, causes much irritation. Rates of infestation usually depend on stocking rates.
The headfly, Hydrotaea irritans, can affect food searching behaviour.
Some of the more important clinical signs are reviewed in this section. It should be stressed, however, that unless certain signs indicated the presence of a disease or a parasite, no treatment should be applied until a veterinarian has been consulted. Any animal that appears to be diseased should be separated from its herd and given veterinary attention.
General clinical signs of acute disease include dullness and depression, loss of interest in avoiding handling, standing away from the herd, victimisation by other deer (causing e.g. kidney injuries), and drooping of the head and ears. The rapid course of many systemic diseases often makes clinical diagnoses very difficult and the stress of handling and examination of a deer in acute stages of disease will often precipitate death. Similarly, the nervous disposition of deer complicates the application of prophylactic treatment in the face of a disease outbreak. When such treatment is indicated, the principle of applying minimal stress must be considered paramount.
The major clinical manifestations of lungworm are loss of condition, retarded growth rates and roughened coats. Consistent coughing and ill thruft are symptoms of infestation.
Clinical signs of gastrointestinal parasitism include scouring, (or diarrhoea), loss of condition, depressed weight gains and failure to thrive.
Apparent signs of haemorrhagic disease include loss of appetite, roughened coat, marked infection of the conjuctiva and other mucosal surfaces, Salivation, nasal discharge, respiratory distress and a swollen tongue.
Treatment of sick deer is analogous with that of domestic animals. Prevention of disease by nutritional management, testing, vaccination, drenching and dipping, is more important than treatment. Prevention of disease and parasitism is best achieved by the routine use of anthelminthics and avoidance of overstocking, as the incidence of disease often increases with high density stocking. Newly acquired stock should be isolated from other deer, treated if necessary, and not released with other deer until they all appear in a healthy condition.
Places where deer are fed special rations are important locations of infection and direct placement of feed on the ground increases chances of it. Deer should therefore be fed in troughs.
Undrenched deer on farms have higher parasite burdens than wild deer. This problem can be overcome if proper drenching procedures are followed. In New Zealand deer are drenched with anthelminthics against stomach and lungworms from 12 weeks to 9 months old.
The dramatic build-up of lungworms observed on some deer farms can be prevented by regular drenching with common antheliminthics and removal of animals to clean pasture.
Most modern anthelminthics appear to be effective in controlling gastrointestinal parasites of deer. Control efforts should be concentrated on young growing stock and incorporate rotational grazing on to clean pasture after drenching.
In the control of liver fluke, known fluke and intermediate host infested areas on farms should be avoided when erecting deer fencing enclosures. Areas within existing enclosures which perpetuate the fluke should be re-fenced, drained or modified to destroy the habitat of intermediate hosts. Treatment of animals infected or at risk is by the use of fasciolicides.
As ticks generally occur less frequently on pastures with few shrubs, rushes or tall grasses, this should be kept in mind when laying out a deer farm.
In general zoonoses can be better controlled among captive deer than in the wild by the application of proper hygienic practices and treatment. Tuberculosis testing of captive deer is very desirable for the eradication and control of the disease.
In Scotland (Sharman, 1978) young deer are tested for the presence of brucellosis and tuberculosis. They are also treated regularly to control warble flies.
It is important for the prevention of the spread of malignant catarrhal fever, as with all contagious diseases, to disperse the herd into as large an areas as possible, and to subject the deer to as little stress as possible, as soon as the disease is diagnosed. Food must be abundant and of a high quality. Addition of an antibiotic, e.g. terramycin, to a feed supplement is the most satisfactory method of treatment of bacterial enteritis as generally most deer will eat concentrates regardless of the presence of the drug.
In China the following methods are used for disease prevention in musk deer:
ensure that stock is in a good health condition;
examine regularly vigour, hair, temperature, visible mucous membrane, breath, tumination, excrement and urine;
routinely sterilize enclosures and utensils;
check on presence of parasites;
eradicate mosquitoes, flies and rats.