Mycotoxicosis

Pig feed, particularly cereals, and bedding, e.g. straw, are frequently contaminated with small fungi which produce toxins both while the crop is growing and after it has been harvested and is being stored. The main genera of fungi involved are Aspergillus spp., Claviceps spp., Fusarium spp. and Penicillin spp.

These fungi produce a range of toxins under the right conditions for multiplication. Two of these, aflatoxin and ochratoxin, suppress the immune system and also appetite. Growth is retarded. There may be teratogenesis. Fumonisin, another mycotoxin, causes immune suppression but what is more obvious to the clinician is that fumonisin causes pulmonary oedema and resulting respiratory signs. The toxins called trichothecenes, including T-2 and deoxynivalenol (DON), which used to be called vomitoxin, cause gastroenteric signs including weakening of the rectal wall, which may result in rectal prolapse. Zearalenone is an oestrogen-mimicking mycotoxin. It will cause infertility and abortions in sows. Their offspring may well have enlarged vulvas. The famous ergot alkaloids are mycotoxins. They will cause gangrene of the ears, tail and teats.

To control the danger of mycotoxicosis farmers should make sure that mouldy feed is safely discarded and not fed to pigs. It is often fed for economic reasons by unknowing pig keepers or by accident when feed bins have been left and not cleaned properly. Wet straw which has been allowed to dry in bales should not be used as litter for any age of pig.

Plant Poisoning

Introduction

Unlike in grazing farm animals, plant poisoning is rare in pigs. The author has seen very few cases and there are few in the literature.

Arum maculatum

This is known as cuckoo-pint or lords and ladies. It is common throughout England but is rare in Scotland. It has long, dark green leaves with radial stalks. It flowers in May with yellowish-green leaf-like spathes which are 15 cm long. The berries are bright red. It is the white tuberous roots which cause the problem for pigs. They are an intense irritant and cause acute gastritis and vomiting. Later the pig will have intense diarrhoea. Death then follows. There is no specific treatment but demulcents are advised. Euthanasia is probably the most welfare-friendly option.

These are the root family that includes sugar-beet, fodder beet, mangles, turnips, etc. They are not toxic to pigs. Unlike ruminants, pigs do not seem to be affected by excess oxalates. However, problems arise in pigs if these roots are cooked and then allowed to cool in the cooking water. Nitrates and nitrites are released which are toxic. Hb is converted into methaemoglobin, a chocolate-coloured compound which does not exchange oxygen. Pigs go blue, convulse and rapidly die of asphyxia. The known antidote is intravenous methylene blue. In the author’s experience this is not successful and euthanasia is advised to prevent further suffering.

Buxus sempervirens

This is box, a common evergreen shrub used as a hedge plant in gardens throughout the UK. It is normally a low hedge but it can be 5 m high. The leaves are elliptical with a notch at the apex. It flowers in April with white flowers. All parts of the plant are toxic. The alkaloid buxine is thought to be the active principle. Pigs are very susceptible to poisoning by box leaves. They vomit and show acute abdominal pain. This is followed by bloody diarrhoea and acute respiratory signs. Death rapidly follows. Treatment is hopeless and prompt euthanasia is indicated.

Conium maculatum

This is hemlock. When consumed in small quantities by sows they give birth to piglets with cleft palates. Normally pigs will not consume sufficient amounts of the plant to cause toxicity.

Daphne mezereum

This is the dwarf bay tree which is sometimes called the spurge olive. It is found in the south of England. It is an erect shrub found in gardens. The flowers are pink and arrive in clusters early in the spring before the leaves. The latter are lanceolate and about 5 cm long. The problem is the red berries, which resemble redcurrants. They are extremely irritant. Only a couple of berries will cause death in a weaner pig. The initial signs are vomiting caused by an acute gastritis. This is followed by collapse and death. The actual toxic substance is not known. There is no specific treatment but demulcents like raw egg and milk are suggested.

Hyoscyamus niger

The universal name for this plant is henbane. It is both an annual and a biennial. It is covered with hairs and has an unpleasant smell. It stands 50 cm high with coarsely lobed, large radial leaves with short stalks. The yellowish-white flowers have a central purple eye. It is the thick, large root which poisons pigs. The active toxins are hyoscyamine, hyoscine and atropine. The plant is found in old monastery gardens where it was grown as a medicine. Pigs will have dilated pupils and dry mouths before going into convulsions. They should be given morphine at 1 mg/10 kg im not only to control the convulsions but also to act as an emetic. There is a chance of recovery if they can be kept warm.

Iris foetidissima

This is the stinking iris which is often called the roast-beef plant. It is found in woodlands throughout the UK. It is an erect perennial plant, 30 cm high, with dark green leaves. It has violet-blue flowers which become bright scarlet seeds. It is the root that causes problems of toxicity in pigs. The pigs will become prostrate and then have violent dysentery. They should be given demulcents as there is normally a chance of recovery.

Lycopersicon esculentum

Nicotiana tabacum

The tobacco plant is very toxic to pigs. The active toxin nicotine will cause rapid death if it is digested in relatively small quantities.

Oenanthe crocata

Carbadox

If this is included in the diet at three times the therapeutic level there will be reduced food intake and poor growth rates.

Carbon monoxide

Levels of over 50 ppm will cause stillbirths and abortions. Such levels are normally due to faulty gas heaters or motor vehicles running in poorly ventilated buildings.

Cyanide poisoning

In grazing animals cyanide poisoning occurs most frequently from eating plants which contain cyanide. This is not the case in the pig, where the most common poisoning is either from pesticides/rodenticides or from waste chemicals from industrial processes such as metal cleaning. Clinical signs which follow a brief period of excitement are dyspnoea, excess salivation and lacrimation, and vomiting. Muscle fasciculation is seen which becomes generalized spasms, staggering, collapse, coma and death. The mucous membranes are bright red, becoming cyanotic just before death. If pigs survive for over 2 h after the onset of signs, they are likely to recover. Heparinized blood can be analysed to establish a diagnosis before death or liver, preferably frozen on post-mortem, can be stored for analysis later. The consistent post-mortem findings are haemorrhages on liver, lung, heart and trachea. As stated earlier all possible intravenous therapy in pigs is extremely difficult. Sodium thiosulfate can be given by mouth. A suitable dosage would be 10 g for an adult sow.

Furazolidone

This medicine has been banned in the UK and the EU. It is a fairly toxic medicine. Three times the therapeutic level will cause ataxia and vomiting. Death does not normally occur as the pigs become anorexic.

Iron toxicity

This can occur from the overdosing of injectable iron in piglets. The piglets will be very depressed and will huddle together. Careful examination will normally reveal physical damage to the muscles at the site of injection where a large dose has been injected. There is no specific antidote. Dexamethazone is suggested at 2 mg per piglet injected im. Death usually occurs within 6 h of the iron injection.

Metaldehyde

This is the active ingredient in molluscicides used in the control of snails and slugs. If is often spilt by mistake on farms. It is normally dyed turquoise. It is palatable to pigs.

There is initially excessive salivation. This rapidly leads to inco-ordination and convulsions. Death is then rapid. There is no specific antidote but anaesthetizing the pig ip with barbiturates might be helpful. The hope is that when the pig recovers from the anaesthetic it will have stopped fitting and can make a recovery. The author has had no success with this treatment.

Monensin

Nitrite/nitrate poisoning

This condition has been recorded in pigs which have been fed on whey and are kept in very poorly ventilated conditions. The pigs will initially show subacute respiratory signs making the clinician consider infectious respiratory disease. The distinctive sign is the lack of pyrexia. They do not cough, but just have laboured breathing. They then collapse and become comatose. Normally they will recover if whey is removed from their diet and they are kept warm. Prevention can be carried out by reducing the quantity of whey in the diet and improving the airflow above the pig pens.

Olaquindox

This is a safe medicine but ten times the prescribed level will cause reduction in growth rates.

Organophosphorus poisoning

Organophosphorus poisoning historically was seen as congenital tremor in newborn piglets. This should not be confused with the congenital tremor seen when sows are affected with CSF in late pregnancy. In fact, congenital tremor may be seen after any acute febrile disease e.g. erysipelas suffered by sows in late pregnancy. It is an alarming condition, with the whole litter of piglets violently shaking. It may also be manifest as only a small percentage of the piglets shaking. Often the piglets will survive if they do not shake so much that they cannot hold the teat. Piglets that are shaking badly should be destroyed.

Paraquat

This is an extremely potent poison. Pigs require very little to show toxic signs. There is initial excitement followed by inco-ordination and convulsions. Acute diarrhoea and respiratory distress are very marked. If only small quantities are involved pigs should be injected with a mixture of vitamin E and selenium.

Phenol

Toxicity can occur after the use of these disinfectants if the pigs are introduced when the pens are still wet. Quite severe skin lesions will be apparent. Pigs should be hosed down immediately and any severe burns should be treated with soothing oily creams.

Salt poisoning

This really is water deprivation and is one of the most common causes of neurological signs in growing pigs. It occurs if the water supply is turned off or frozen up. A growing pig weighing 15 kg requires 2 l of water per day. Pigs do not like to wait for water and it is very important that there is a ready supply available to them. This is important when the piglets are still suckling the sow. A 100 kg finishing pig requires 12 l daily. Pigs do not like to queue so adequate nipple drinkers of clean fresh water should be available. Neurological signs are more prominent in growing pigs. When the supply of water is reinstated the water should be controlled. In severely affected pigs, dexamethasone injections will help with recovery.

Selenium poisoning

This is extremely rare. The author has seen the condition in pigs which were given a large amount of an equine supplement. The fattening pigs remained mentally alert but were reluctant to rise. In fact they appeared unable to rise for 12 h. There was no specific antidote available. They recovered with careful nursing.

Pigs will consume rat bait containing warfarin. The signs of toxicity are coughing up blood, bloody diarrhoea and haemorrhages visible in the skin. Aggressive treatment with intramuscular injections of vitamin K will normally be successful.

Reactions to Medicines

Penicillin

If procaine penicillin is inadvertently injected iv, pigs will show immediate trembling. They will recover in a few hours without treatment.

Tiamulin

Rarely tiamulin, if fed at standard therapeutic levels for the treatment of swine dysentery, will cause adverse reactions. These may be just a slight reddening or in extremely rare cases death will occur. In these cases haemorrhages will be seen in the myocardium.

Causes of Sudden Death

Iatrogenic causes of sudden death

Sudden death is a misnomer. In reality it is found dead since last seen. The owner will very rarely see an animal die. It is even rarer for the clinician to see death. Sadly when such deaths occur it is usually at the time of veterinary treatment. Possible iatrogenic causes of sudden death are:

• Anaphylaxis from administration of medicines.

• General anaesthesia.

• Restraint leading to cardiac arrest.

• Lumbar/sacral epidural.

• Massive haemorrhage (this could occur at parturition where there is no human involvement).

• Intra-arterial injection.

• Intravenous injection.

• Sedation.

Reasons for animals to be found dead

African swine fever

It is unlikely that every pig will be found dead. The sick animals will have had an extremely high rectal temperature which drops before the clinical signs of marked cyanosis of the skin and inco-ordination develop. There will be severe haemorrhages throughout the body, particularly in the lymph nodes. Tissue or body fluids can be used to demonstrate antibody. Frozen sections of tissue may be used to demonstrate virus which may also be isolated from cultures of buffy coat leucocytes. The ultimate diagnostic tool is animal transmission.

Anthrax

Pigs found dead are not the normal manifestation of anthrax except in young pigs. Older animals will show throat swelling. Samples of this throat swelling should be collected to prepare slides for staining with methylene blue. The spleen may be enlarged but this is not an invariable finding.

Aujeszky’s disease

Sudden death will occur only in young pigs. Older pigs will show neurological signs. Adults may show few signs. There will be few gross post-mortem findings. Virus may be isolated from frozen tonsil section. PCR may be used on fixed tonsil, brain or nasal swabs.

Bowel oedema

This is a disease of newly weaned pigs. Some of the litter may be found dead. The remainder will have the characteristic oedema of eyelids, larynx, etc. The post-mortem will reveal excess peritoneal, pleural and pericardial fluid. The isolation of specific Escherichia coli serotypes from the small intestine will aid diagnosis.

These will show variable post-mortem pictures. They are itemized above.

Classical swine fever

Only in the hyperacute disease will some young pigs be found dead. Other pigs will show high fever and conjunctivitis. Postmortem may not show any gross lesions in the hyperacute cases but less acute cases will show a haemorrhagic skin and internally the lymph nodes will be very inflamed. There are splenic infarcts. Virus can be demonstrated by FAT on frozen sections of the tonsil. Virus may also be demonstrated from RT-PCR from the lymph nodes. Serology using ELISAs will be helpful, with animal transmission as the final definitive test.

Clostridiosis

This will cause sudden death in baby pigs with the characteristic ‘port wine-coloured diarrhoea’. There will also be sudden death in adults and large fat pigs. There is rapid decomposition of the carcass. There is tracheal froth and pulmonary oedema. There is an ‘Aero chocolate’ liver. Clostridium novyi may be identified in the liver with FAT or PCR.

Coliform mastitis

This will cause sudden death only in newly farrowed sows. The glands will be swollen and hard without any secretion. The organism may be cultured from an infected gland.

Cystitis/pyelonephritis

Cystitis will not cause sudden death and in fact pyelonephritis will very rarely cause acute symptoms. Sudden death occurs only when both kidneys are affected from an ascending infection from cystitis with a toxic E. coli strain. Post-mortem will reveal the infected kidneys.

Drowning