Virtually all deer farmed in Britain are red deer (Cervus elaphus). Other species, especially fallow deer (Dama dama), are common in deer parks where the deer are subject to low levels of intervention in comparison with farmed deer. Red deer have proven to be more amenable to the regular handling and more invasive procedures that characterise deer farms.
But red deer have not been selectively bred in the same way as conventional livestock, and consequently are not yet subject to diseases associated with high productivity, such as mastitis, ketosis, hypocalcaemia, etc. The number of diseases having an economic impact on deer farms is thus rather limited and of all protein production systems, deer farming must use the least quantity of antibiotics. However, because deer remain effectively wild, they are especially susceptible to stress, which may cause subclinical conditions to become apparent.
It must be remembered that no drugs are licensed for use in deer in the UK.
Parasites
The only diseases which are routinely treated prophylactically are parasites. Lungworm (Dictyocaulus eckerti; Figure 1) is the most common cause of clinical signs and probably the biggest cause of financial loss and mortality, although gastrointestinal nematodes are possibly of increasing importance.
In New Zealand, pour-on anthelmintics have been incriminated in the development of drug resistance. Whilst they may provide longer protection, pour-ons do not achieve the levels of drug in the blood provided by oral and injected routes. Administration by mouth or injection is preferred and all of the available macrocyclic lactones are used, with moxidectin perhaps the most effective. Levamisole is ineffective in deer. Changing the drugs used and treating with combinations of anthelmintics may delay the development of drug resistance.
Faecal egg and larval counts should be treated with circumspection. Samples must be absolutely fresh, and it should be remembered that the counts only relate to adult parasites. Obviously, management to provide as clean pastures as possible by rotation, grazing aftermaths and reseeds (especially using chicory, red clover, brassicas, etc), mixed grazing with cattle and sheep and lower stocking densities are all good practice.
Red deer develop good resistance to lungworm and gastrointestinal parasites, and it is common practice to restrict use of anthelmintics to calves and yearlings. Worming of calves pre-rut, which normally coincides with handling for other purposes, is important.
Other parasites, such as deer warbles, nostril maggots and lice, are also eliminated or reduced by anthelmintics.
Liver fluke (Fasciola hepatica) is a common cause of liver condemnation in red deer but does not normally cause clinical disease. Closantel is contraindicated, causing well-documented adverse reactions.
Toxoplasma gondii is increasingly causing abortion in New Zealand red deer but has not yet been recognised in Britain as a cause of abortion.
Cryptosporidium parvum can have a serious impact, with mortality of up to 20 percent among young calves born outdoors. In some herds, this may reappear for several years before resolving apparently spontaneously.
When naïve red deer are moved into areas with high tick populations, mortality can be high as a result of infection with Babesia.
Bacterial diseases
Amongst the bacterial diseases affecting farmed red deer, mycobacteria are economically the most significant. Johne’s disease caused by Mycobacterium avium paratuberculosis (MAP) is widespread, although it may be clinically inapparent where grazing is abundant and deer are well nourished. Deer are susceptible to both cattle and sheep strains and presumably can also become infected due to contact with wildlife.
Deer are infected early in life and possibly in utero. They often differ from cattle and sheep in becoming clinically affected as yearlings showing delay in shedding their winter coat, failure to gain weight and eventually chronic diarrhoea. There are no available measures to control Johne’s, although farmers with infected herds should cull yearlings that are not thriving. Ensuring good grazing and management may reduce shedding of bacteria.
M. avium avium (avian tuberculosis) can cause mortality in housed calves around weaning and also in adults, causing visible lesions which cannot be distinguished from those caused by bovine tuberculosis without culture.
Red deer are susceptible to bovine tuberculosis (M. bovis), although they are considered a dead-end host of limited epidemiological significance in spreading disease to cattle. Where farmed deer herds have become infected, losses have been sporadic but internal and external abscesses can be common. The retropharyngeal and mesenteric and mediastinal lymph nodes are the most commonly infected. Infection spreads more quickly where herds are of mixed social groups presumably due to social stresses.
The comparative cervical skin test using avian and bovine tuberculin remains the standard test for the disease in deer. It has not been validated but remains a useful screening test, especially where large numbers of deer are being tested. At the time of writing, several serological tests are being evaluated. Without better tests, it is not easy to create a statutory testing regime but, in the meantime, deer farmers must exercise extreme caution in moving deer from high-risk areas or herds of doubtful status. As a notifiable disease, any suspicions of tuberculosis must be reported. This is most likely to occur following identification of visible lesions at meat inspection.
Farmed deer do not appear to contract clostridial diseases very often and few farmers vaccinate. Sporadic cases of enterotoxaemia caused by C. perfringens type D (pulpy kidney) is probably the most common, but other types, even including tetanus, have been reported.
Of greater significance is Yersinia pseudotuberculosis, which affects calves. This is normally subclinical and results in good immunity, but occasionally calves at, or just after, weaning that have been stressed due to rough handling, changes of nutrition, transport or bad weather will develop clinical disease. This is normally manifested as sudden death but occasionally foetid diarrhoea and recumbency may be seen. At post-mortem, there is a severe haemorrhagic gastroenteritis with fibrinonecrosis (Figure 2) of small and large intestine and necrosis and haemorrhage of the mesenteric lymph nodes. Where a group of deer are affected, losses can be very high and this is one of the few indications for the urgent administration of long-acting antibiotics to all in-contacts.
E. coli O157 has been identified in healthy deer, though a recent project in which a large number of farmed and wild deer were screened suggests that the prevalence is much lower than in cattle.
Viral diseases
Amongst viral diseases, malignant catarrhal fever causes sporadic losses in adult deer resulting from contact with healthy sheep – usually around lambing. Normally death occurs within 12 hours but affected deer may survive much longer with mucopurulent discharge from the eyes and nose (Figure 3).
Herpesvirus of Cervidae (HVC-1) can cause disease in newly weaned calves, which may present as conjunctivitis that can lead to corneal opacity with mucopurulent discharge. This virus is related to infectious bovine rhinotracheitis and most deer are seropositive, but outbreaks of disease are rare.
Red deer have been shown in the laboratory to be able to contract foot and mouth disease (FMD) but it is doubtful whether any wild deer have contracted the disease and no cases of clinical disease or seroconversion occurred during the 2001 FMD outbreak, despite widespread high populations of wild deer and in-contact farmed deer.
Other health considerations
The spongiform encephalopathy known as chronic wasting disease has spread throughout the USA since it was first recognised in the 1970s and it has now been diagnosed in Scandinavia. It does not appear to be infectious to humans but is transmissible between deer by fomites and mortality rates can be high. There is widespread concern that this disease could enter the UK.
Deer are not often affected by plant poisons – they eat yew, for example, with impunity – but sudden access to acorns has caused disease and hand-reared calves died as a result of eating foxgloves.
Copper deficiency presents in adult red deer as ataxia with conspicuous loss of coordination of the hind quarters and affected deer may struggle on for many weeks. Calves in copper deficient herds can usually be identified in late summer as having swollen hock and knee joints. Farmers frequently administer boluses to all deer although evidence that this improves performance in healthy herds is limited.
Deer are highly susceptible to ruminal acidosis, usually due to accidental access to cereal-based concentrates. Changes of diet must always be carried out with care.
High carbohydrate diets such as potatoes, especially in the absence of palatable forage, often results in laminitis and overgrown hooves. Clipping of hooves and hard floors may allow affected deer to make a good recovery. Other problems of the feet are uncommon; occasional abscesses occur, often due to injury (usually at handling). Traumatic injuries are relatively common in deer and even fractured limbs may resolve spontaneously without permanent lameness.
Finally, it must be emphasised that deer are not well insulated and have low energy reserves but are adept at finding shelter. It is important that farmed deer have access to woodland or ground which provides shelter from wind
FURTHER READING
The Veterinary Deer Society has published a handbook, Management and Diseases of Deer, which is now available on disc from Mark Dagleish (mark.dagleish@moredun.ac.uk).
For over 30 years, the Deer Branch of the New Zealand Veterinary Association have published annual proceedings of their deer courses. These are available online from: info@sciquest.org.nz. For more information, visit: sciquest.org.nz/deer.
For the general biology of deer, refer to: Fletcher, J. (2014) Deer. Reaktion, London.
The book Farming Wapiti and Red Deer (1993) by Haigh, J. C. and Hudson, R. J. is an invaluable source, but unfortunately is no longer in print.
