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Diseases in the Mute Swan

Sally L. Goulden BvetMed, MRCVS

The Swan Sanctuary

Felix Lane, Shepperton

TW17 8NN

 

I INTRODUCTION

This session will review the conditions commonly encountered in the Mute swan, with methods of treatment. A brief life history and section on general care and handling are included.

II LIVE HISTORY

The Mute swan is a large, white, sedentary, fiercely territorial waterfowl found on a large number of waterways in the UK. Breeding starts at 3 to 4 years of age, birds often pairing for life. Nest building and courting behaviour begin in February, nests being built usually on ground near the waters edge. The female incubates the clutch of 5-7 eggs for 30 days. Male and female care for the cygnets, who are hatched during May to July covered in down and ready to swim. Weed is pulled up and the water trodden to disturb sediment for the cygnets to feed. Parental care generally lasts for 7 months, the juveniles being regarded as adults as their brown plumage is replaced by white, and then are chased away. They tend to flock until they are of breeding age. Swans can live for up to 25 years.

III GENERAL CARE, HANDLING AND PROCEDURES

The Mute swan is very territorial and aggressive in the wild, but responds well to a quiet calm approach and environment. Removal from the water is often achieved by swiftly pulling the head after tempting with food. For transporting, tie the humeri together over the dorsum using a piece of stretchy bandage or lengths of old pair of tights. Use same to tie legs together over tail. Carrying the bird is easiest under the arm to pinion the wings, while the head can be gently controlled with the other hand.

Swans get very stressed when kept near cats and dogs, and depressed if kept away from other swans, especially members of a family group around breeding time. Recovery can be severely impeded if these factors are not considered.

Feed from a washing-up sized bowl, full of water, bread, grain, grit and greens. Some assistance may be needed to introduce the bird to this method of feeding.

Routine worming on admission to the sanctuary has not been found necessary or desirable (consideration of the effects of the excreted drug residue on the environment).

Aim to allow access to water for bathing, swimming and washing as soon as possible. 24-48 hours with access to a small pool is necessary for swan to regain waterproofing.

Release as near to where found as possible, because of territory. This may not be possible in cases where water contamination was the original problem, or if an amputation has been necessary.

Release on fine day with several hours of daylight left.

General anaesthesia.There is no requirement for pre-operative withholding of food or fluids or for pre-medication.

We use intra-operative i/v fluids (usually Hartmanns) introduced via a 23 or 25 G i/v cannula through the medial tarsal vein. Anaesthesia is induced with propofol(Rupinovet) at 0.Srnl/kg (adult average body weight around l0-l2kg).Maintain with Isotlurane (Abbott) delivered by uncuffed endotracheal tube (about 6mm for adult,taped around beak with Elastoplast or similar) and Dams circuit (Oz flow 2-4 I/mm,Isoflurane around 2.5 to 4%).

Nitrous oxide is occasionally necessary, used at 0.2-0.5 I/rain, no higher.

Monitoring of anaesthesia is not as straightforward as with mammals. We use a

respiratory monitor, but respiration is occasionally not strong enough for this to work well. Heart is monitored with a stethoscope, pulse on the axillary artery. Neither the palpebral reflex nor the eye position are useful. Pedal reflex is used.

Many operations are carried out with the bird laterally recumbent. A towel is rolled and placed between the keel and the table to allow ventral movement during respiration

Debilitated birds often require intravenous fluid therapy, around 1L per day for an adult.

Medication via the parenteral route is preferred to oral where possible.Injection site commonly used is the skin or muscle caudal to the tibia

IV DISEASES

As in all cases, history, if available, can be very helpful.

COMMON CAUSES OF INJURY:

Angling-related; crashes; territorial fights; wife beating; shooting; water craft dog bites; mink bites; electricity burns from overhead power cable; leg rings.

INTOXICATION:

lead and other metals; Botulism, oil contamination.

Infections: Aspergillus; Duck Virus Enteritis (DVE).

INJURY

Angling-related

Many hooks and lines can be removed on the river bank, needing no further treatment. Hook and line injuries account for about 30% of our surgical cases.

Examine all of bird including under tongue and under rami of mandibles. Sub-cutaneous soft-tissue swelling in the cervical area often is hook. May cause respiratory embarrassment, severe infection, inanition, weight loss. Diagnosis assisted by radiography.

Hooks generally need removal if in the cervical oesophagus. They can wall off BUT can also cause large tears leading to potentially fatal abscessation or jugular vein rupture.

Remove under general anaesthesia. Position bird in left lateral recumbence. The skin bleeds profusely, so apply artery forceps to incision site before cutting. Repair oesophagus with 2 layers of suaged on silk. Outer layer inverted sutures. Severe infection is often present: leave skin unsutured or parfially suture and treat as an open wound. Beware surgical debridement as swan pus is very thick (like lasagne), stripping can damage underlying structures. Use chemical debridemen: ( also use on other infected wounds). Honey is very good (set honey, doesn’t matter what flavour!)

Hook removal from the mouth may need to be done under general anaesthesia. Large curved haemostats are useful, especially for the bastard spot! Hooks reaching the gizzard are NO TROUBLE, and will be pound down. Proventiculotomy is indicated if a lure or float have been swallowed. They usually lodge in the gizzard but the proventriculus heals more easily and allows sufficient access. Approach via ventral midline coeliotomy, no need to repair air sacs.

Line wrapped around limbs can cause severe injury and may even necessitate limb amputation. Wounds often bleed profusely as line is removed.

Shooting.

Air gun or rifle pellets are most common. One case of ball bearings fired from a sling! We don’t usually remove pellets unless they are near the eye or jaw. Fibrosis is the main problem. Lead toxicity does not occur because the pellets become walled off.

Bites.

Become infected with necrotising bacteria and can be fatal. DO NOT SUTURE. Mink can kill cygnets with one bite to the dorsal thoracic arm.

Electricity cable burns

Large areas of tissue can necrose and slough off several days after the accident, but perseverance with even the largest of wounds is often rewarded.Nervous problems.

Often caused by crashes, also see botulism and lead toxicity. Ataxia, inability to stand, limb paresis or paralysis may all improve with time (up to 8 weeks). Suspect crash involvement if the bird is found sitting in the middle of a field underneath some electricity pylons. Inspect for other wounds or signs of burns. Spinal damage often accompanied by uncontrolled tail wagging. Some pedal or leg soft tissue injury causes severe secondary selftrauma, possibly due to nerve ending damage. 1 case ofbilateral otitis mediaOrthopaedic problems.

Often caused by crashing. Amputation is indicated if the limb distal to the fracture becomes necrotic, or if the limb remains dysfunctional. Absence of infection allows you to give the bird some time to show improvement. Intra-medullary pinning is rarely successful because:infection cannot adequately be controlled;the thin cortex often splinters;the large air filled medullary cavities do not allow any purchase for the pin.there is very often concurrent nerve damage and the limb requires amputation anyway.We occasionally use horizontal pinning for the tibia and hold the pins in place with microscope slide carriers filled with Araldite. We have had lots of success using Animalintex as a splint- applying wet, bandaging into place and allowing to dry. Air sac leakage can occur, often as a result of crashes. There are continuations of air sacs in the humerus and in some cervical vertebrae.

Two developmental conditions are seen: aeroplane wing, where the ligaments of the carpus are lax, resulting in lateral rotation of the mama No remedy has been found, amputation often being the only solution;medially or laterally luxating digital flexor tendon in the leg. Usually a result of aberrant growth of the distal tibjo-tarsal bone. No solution here either.

INTOXICATION

Lead

Lead sinkers used in freshwater fishing are ingested and ground down in the gizzard. Sale to and use of by fishermen of lead ledger and split lead shot wider 28gram has been banned since January 1987. The incidence of lead poisoning has dropped greatly but still occurs. There is still lead used in some parts of the country. There is also some residual lead in river silt, ingested by swans because of their long reaching necks, especially when the river levels are low. ingestion of lead shot from shooting will also cause lead intoxication.

Clinical signs include: loss of righting reflex. ataxia, convulsions and coma (especially in cygnets); flaccid paralysis; a characteristic neck kink; gaping; anaemia; intestinal impaction; cephalic oedenia, bright green diarrhoea.

Recrudescence is likely during the breeding and moulting season, when nervous signs may reappear or feather bleeds occur.Diagnosis is not straightforward but radiography of the ataxic/paralysed swan to find radio-opaque particles is useful. A distended gizzard may also be apparent. Blood lead levels can be useful, but have disadvantages. Normal values are O.5-2.O ppm, but some Thames birds have very high `normal’ levels. Time delay before results return. Supportive therapy very important Calcium EDTA chelating therapy according to severity of signs. DO NOT attempt gizzard flushing. General anaesthesia risk is increased in leaded birds, and damage may be done to the lower oesophageal sphincter. Supportive care is very important. Botulism.Occurs almost exclusively in hot dry weather. Often massive die-offs affecting many species in one water area. Signs easy to confuse with lead poisoning. Flaccid paralysis, bird generally looks a lot sicker than with lead. Don’t get convulsions. Bird often lies with head back between wings. Supportive care and stress-free environment very important May take several weeks to recover.OilDifferent types of oil cause different severity of problems.Internal toxicity:

GIT ulceration, renal failure. Charcoal or Pepto-Bismol in foodExternal problems:

hypothermia, loss of water-proofing and drowning. Wash bird and rinse thoroughly, many litres of water at correct temperature necessary. Success rate depends on speed of cleaning. Delay wash process until birds fit enough. Allow birds time to re-waterproof

INFECTIONS

Aspergillosis

Common in waterfowl due to mouldy feed. Difficult to diagnose, but assume has it if has dyspnoea and/or rattling wet cough. Can be fatal. Combination of Amphotericin B and Rifampicin used.Duck Virus Enteritis (DVE)

Herpes virus, strains of differing virulence. We have seen:Peracute type: massive die-off( 100+ birds) in short time, minimal clinical or postmortem signs.

Acute type: birds appear sick, lethargic, tend to die in water. Greater time between deaths, but still significant numbers die. Clinical signs can resemble Botulism but tends to happen around April time. In addition will get diarrhoea with or without blood, haemorrhage from mouth or nose.Can also get carrier state.Post mortem signs: characteristic raised yellow caseous plaques along ridges of lower oesophagus; button ulcers along small and large intestine, especially caeca and cloaca. May get petechiation or ecchymoses on GIT or pericardium; tiny white foci on liverDiagnosis by postmortem exam findings and virus isolation.

Prevent spread by REMOVING BIRDS FROM WATER.

Commonly used Drugs

DRUG

Trade name / Manufacturer

Dose rate
Amphotericin B

Fungizone, Squibb

1.5 mg/kg tid i/v, concurrently 1mg/kg bid /trachea,and also with Rifampicin.
Amoxycillin

Clamoxyl LA, Smith Kline Beecham

adult 2.Sml SQ alternate days
Carprofen

Zenecarp, C-vet

I .Sml SQ post-op adult dose
Calcium Edetate

Calcium EDTA strong, Animalcare

O.75m1 in 2.5m1 sterile water i/rn on every 2nd or 3rd day. repeat oourses as necessary. Severe cases 4-6m1 in drip over 24hrs. Ring Swan sanc for advice
Dexamethasone

Dexadreson, Intervet

0.25m1 SQ daily for 2-3 days only.
Enrofloxacin

Baytril 5%, Bayer

Omgfkg SQsid.
Epsom saltsin feed
Honey

set, any brand

very effective, cheap debriding agent
Fenbendazole

Panacur, Hoechst

100mg/kg po single dose
Iverrnectin

Ivomec, MSD Agvet

200ugfkg SQ single dose
Intrasite

Smith & Nephew

good debriding agent for wounds
Penicillin

Crystapen 600mg, Britannia

i/v in drip, 600mg
Rifampicin

Rifadin,Merrell

30mg/kg po tid.
Potentiated sulphonamide

Borgal, Hoechst

3-SmI SQ sid
Spectinomycin

Spectam, Sanofi

irn l.Srnl SQ adult dose sid
Vitamin B12

Anivit B12

l-3m1 SQ sid

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