Black''''s veterinary dictionary 21st edition - N potx

Nairobi Sheep Disease Nairobi sheep disease is an acute infectious fever of sheep and goats, caused by a bun-yavirus, and occurring in eastern and southern Africa.. In horses lame as a r

Nagana is an unscientific but convenient name

for trypanosomiasis transmitted by tsetse flies

(Glossina spp.) in Africa The trypanosomes

involved are Trypanosoma vivax, T uniforme,

T congolense, T brucei, T simiae, and T suis

(See TRYPANOSOMES.) The symptoms of nagana

include anaemia, intermittent fever, and (except

in pigs, in which the disease may be very acute)

a slow, progressive emaciation In both horses

and dogs the eyes may be affected, as shown by

corneal opacity Horses often have oedema

affecting the limbs and abdomen Cattle may

abort

The drug quinapyramine is used (among

others) in treatment

The kudu, hyena, and bush-buck, as well

as other wild animals, act as reservoirs of the

infection

Nail Binding

(see INJURIES FROM SHOEING)

Nails (Claws)

A claw contains a matrix with blood vessels,

nerves, etc., from which it grows and is

nour-ished Lying within the matrix is the bone of

the terminal phalanx of the digit, which gives

the nail its characteristic form in the different

animals When not in use in the carnivora, nails

are retracted by ligaments in an upwards

direc-tion; this is more marked in cats, where the nail

may almost disappear, than in dogs

Nails, Diseases of

The nails of cats and dogs sometimes become

torn or broken through fighting or accidents

Sometimes only the tip is injured, and the

matrix higher up is undamaged; in such cases a

fine pellicle of horn covers the tip until such

time as the horn has grown down from above,

and the whole nail is not shed In other cases

infection occurs, causing great tenderness of the

part

Ingrowing nails occur upon the ‘dew

claws’, on the insides of the paws of dogs These

more or less rudimentary digits do not touch

the ground, and are consequently not subjected

to wear from friction The nails grow, and

owing to their curve eventually penetrate the

soft pad behind them Where actual penetra-tion has occurred, the nail should be cut short and an antiseptic dressing applied It is custom-ary for owners of sporting and other dogs to have the dew claws removed during puppyhood

to avoid future trouble of this nature Amputation of dew claws can be carried out in the adult under anaesthesia

Onychomycosis, or a fungal infection of the claws, is a not uncommon condition in cats, and is of public-health importance as a reservoir

of ringworm transmissible to children (See RINGWORM.)

Nairobi Sheep Disease

Nairobi sheep disease is an acute infectious fever of sheep and goats, caused by a bun-yavirus, and occurring in eastern and southern Africa The virus is transmitted by the tick

Rhipicephalus appendiculatus.

SignsImported sheep usually show an acute febrile disturbance within 5 or 6 days after being infected by the ticks This lasts for up to

9 days and then a fall in temperature occurs and other clinical symptoms appear Death may take place a day or two later, or a further rise in temperature may be shown, death or recovery following There is rapidity and difficulty in breathing, a mucopurulent nasal discharge and green watery diarrhoea, which may contain mucus or blood The genital organs of ewes are swollen and congested, and abortion may occur

in pregnant ewes

Immunity In the great majority of cases, recovery confers a strong and lasting immunity This is also possessed by sheep in areas where the infection is endemic

Nanogram (ng)

A unit of weight equivalent to 1000 micrograms

µ1000 micrograms equal 1 milligram (mg)

Nanometre (nm)

A unit of linear measurement used in e.g

virolo-gy One nm equals one millionth of a millimetre

Naphthalene Poisoning

Naphthalene poisoning might arise from the ingestion of moth-balls In the dog, it has been shown experimentally to give rise to

haemolyt-ic anaemia (In children, poisoning from moth-balls gives rise to ‘port-wine coloured’ urine.) Another symptom is cataract Chlorinated naphthalenes have been identified as one cause

N

of HYPERKERATOSIS in cattle; and tear stains

may be a symptom of this type of poisoning

Narcolepsy

Narcolepsy is a sudden collapse into deep sleep

It has been recorded in dogs, and may be

part-ly genetic in origin A case was recorded in the

UK in a 3-year-old Corgi which sometimes

collapsed when taken for his first walk of the

day, or offered food Often yawning and a

vacant expression would precede a sudden drop

from a standing position to a sitting one or a

lying one No excitement, salivation, or

convul-sions were seen, and at other times the dog was

active and mentally alert; he was easily aroused

after he had collapsed Electro-encephalograms

supported the diagnosis The condition has also

been recorded in daschunds, dobermanns,

labradors and poodles

Nares

Nares is the Latin word for the nostrils

Nasal Bot Fly (Oestrus Ovis)

Larvae

Nasal Bot Fly (Oestrus Ovis) Larvae are serious

parasites of sheep (See under FLIES.)

Nasal Disorders

(see NOSE & NASAL PASSAGES,DISEASES OF)

Naso-Oesophageal Tubes

Narrow tubes inserted through the nose into

the stomach They are tolerated by many, if not

most, cats, and can be used to provide

nutri-tional support via liquid foods for a week or

two The use of small-diameter tubes does not

prevent voluntary intake of food

Naso-Pharynx

The upper part of the throat lying posterior to

the nasal cavity

Natamycin

An antibiotic used for the treatment of

ringworm in cattle and horses Application

can be made with a knapsack sprayer

(See RINGWORM.)

National Scrapie Plan

A long-term UK plan which aims to reduce

and, eventually, eradicate the number of sheep

not genetically resistant to scrapie and other

transmissible spongiform encephalopathies

Under the scheme, sheep are individually

iden-tified by electronic tag, and blood-tested to

establish whether they are susceptible or

resis-tant to scrapie Sheep identified as susceptible

must not be bred from Under DEFRA propos-als in 2003, farmers with confirmed scrapie cases on their farms will have their flocks geno-typed so that the more susceptible sheep can

be identified and removed, or the whole flock disposed of

National Office of Animal Health (NOAH)

Founded in 1986, to represent those UK com-panies which manufacture animal-health prod-ucts licensed under the Medicines Act Address:

3 Crossfield Chambers, Gladbeck Way, Enfield,

Middlesex EN2 7HF Publications include: The

Safe Storage & Handling of Animal Medicines; Poisoning in Veterinary Practice.

National Pet Register

This provides a service for reuniting lost pets with their owners, and also for third-party liability Address: Heydon, Royston, Herts SG8 8PN

Nature

Oedema of the udder (see under OEDEMA)

Navel-Ill

(see JOINT-ILL)

Navicular Bone

Navicular bone is the popular name for the sesamoid of the 3rd phalanx of the horse It is a little boat-shaped bone, developed just above the deep flexor tendon, and serves, as do all sesamoid bones, to minimise friction where the tendon passes round a corner of another bone

It enters into the formation of the ‘coffin-joint’, between the 2nd and 3rd phalanges of the digit

It is of great importance in deep punctured wounds of the foot when these are situated towards the heels, for, when damaged, its sur-face becomes inflamed, the inflammation spreads to the coffin-joint and may produce incurable lameness

Navicular Disease

Navicular disease is a chronic condition of inflammation affecting the horse’s navicular bone and its associated structures The fore-feet are usually both attacked, though the condition may arise in only one of these, or in the hind-feet (rarely) Ulceration of the cartilage first, and later of the bone on the surface over which the deep flexor tendon plays, may sometimes be seen at autopsy

CausesThese are still a matter of hypothesis rather than certainty, and controversy persists

480 Narcolepsy

N

Some authors have referred to increased

vascu-larisation of the navicular bone; others suggest

that ischaemia may be responsible, leading to

pain and, if at least 2 of the distal arteries are

occluded, to chronic lameness In horses lame

as a result of navicular disease, occlusion of the

main artery and progressive arterial thrombosis

are frequent, with a resulting area of ischaemic

necrosis and cavitation of the navicular bone

Another view is that the disease is not caused

primarily by ischaemia and subsequent

necro-sis, but is a consequence of bone remodelling

due to altered pressure from the deep flexor

ten-don and increased load on the caudal part of

the foot – the condition not being irreversible

unless secondary lesions such as adhesions

and bony spurs have developed Special shoeing

to alter the load on the navicular bone is

recommended

Signs Navicular disease usually develops so

slowly that the owner has considerable

difficul-ty in remembering exactly when the first

symptoms were noticed In fact, little or no

importance may be attached to the almost

char-acteristic ‘pointing’ of one or both fore-feet,

because ‘he has always done that’ ‘Pointing’

consists of resting the affected foot (or feet) by

placing it a short distance in advance of

the other when standing in harness or in the

stable When both feet are affected, each is

alternately pointed Later, the horse may go

lame or be tender on his feet at times, but with

a rest he generally becomes sound again As the

disease advances, he may either start off in the

mornings stiff and become better with exercise

as he warms to his work, or may become lame

as the day goes on Sooner or later, however,

there comes a time when he will go

permanent-ly ‘pottery’, or ‘groggy’ The length of the stride

decreases and there is difficulty in advancing

the feet, so it looks as if the shoulder is the seat

of the lesion When made to turn, the horse

pivots round on the fore-feet instead of lifting

them, and when made to back, drags the toes

If the shoe of such a horse is examined it is

usually found to be more worn at the toes than

at the heels In fact a ‘groggy’ horse may wear

his shoes quite thin at the toes before the heels

show much sign of wear at all In the final

stages the horse becomes distinctly lame and

unfit for work When observed in the stable he

is noticed to be continually shifting from one

foot on to the other, and the resting foot is

placed well out in front

Treatmentmust aim at the relief of pain and

improvement of the local blood circulation The

vasodilator isoxuprine or a formulation of war-farin may be added to the feed of horses; the dosage of warfarin requires great care – with overdosage there is a danger of haemorrhage Warfarin treatment has been reported effective

in about 75 per cent of cases of navicular disease Before the advent of drug therapy it was cus-tomary to perform the operation of

neurecto-my, which consists of a section of the plantar or median nerve of the limb In a favourable case, following operation, the horse becomes appar-ently sound, although the diseased condition is still at work in the bone No pain is felt, and the horse is fit for light work at slow paces The feet require constant attention to ensure that no stones, nails, etc lodge in the hoof, for even when these inflict serious damage the horse still goes sound, not feeling the pain

Navy Beans

Navy beans may cause death if fed raw (See LEGUME POISONING.)

Near East Encephalitis

An alphavirus infection of horses and donkeys; less frequently of cattle and sheep Convulsions/paralysis may follow fever and precede death (See EQUINE ENCEPHALITIS;

BORNA DISEASE.)

Neck

In animals, the neck is that part of the body connecting the head with the trunk It contains the trachea, oesophagus, blood vessels, the spinal cord and cervical vertebrae Both the mouse and giraffe have 7 cervical vertebrae, as

do most mammals

The weight of the head is supported by the

powerful ligamentum nuchae, which takes the

strain off the muscles, thereby avoiding fatigue

In the horse the ligament extends from the spines of the withers to the posterior of the occipital bone of the SKULL

Necrobacillosis

Damage of an organ, or tissue, caused by

Fusobacterium necrophorum The necrotic area

has a characteristic rotting odour

Necropsy

Examination of a dead body (see AUTOPSY)

Necrosis

Death of cells or of a limited portion of tissue

Necrosis (Bacillary) or Necrobacillosis

(see CALF DIPHTHERIA)

Necrosis (Bacillary) or Necrobacillosis 481

N

Necrotic Enteritis

A subacute or chronic enteritis which follows a

more severe episode caused by infection with

Salmonella spp or Campylobacter sputorum

var mucosalis A condition of unweaned and

older pigs, characterised by scouring and loss of

condition

The lesions are in the caecum and ileum (See

also under ILEUM.)

Cold, damp, dirty surroundings appear to

predispose to necrotic enteritis (See PORCINE

INTESTINAL ADENOMATOSIS.)

Necrotic Enteritis in Chickens

A disease of chickens characterised by

unthrifti-ness and diarrheoa caused by Clostridium

perfringens (welchii) type C There is usually a

concurrent defect in nutrition The disease has

been reported in most European and North

American countries, and in Australia

Necrotic Stomatitis

A serious infection of the inside of the mouth

and the tongue, seen in calves; it may also be

found in reptiles (See CALF DIPHTHERIA.)

Negri Bodies

Negri bodies are comparatively large, rounded

bodies in the brain cells of animals infected

with rabies Their presence can be

demon-strated by staining with Seller’s stain, among

others The cerebral cortex, Ammon’s horn,

and the Purkinje cells of the cerebellum are

the main sites to examine The diagnosis

of rabies once depended upon the

demonstra-tion of Negri bodies in the affected animal (See

RABIES.)

Neisseria

Spherical, Gram-negative bacteria, some of

which are associated with eye infections

Nematocide

A drug that destroys nematodes

Nematode

Nematode is a general term applied to the

para-sitic Nemathelminthes, which include the

round-worms, as distinct from the Platyhelminthes, or

flatworms (See WORMS.)

‘Nematode Poisoning’

In the USA, larvae of Anguina agrostis on

Chewing’s fescue in immature hay caused an

outbreak of poisoning in cattle Symptoms

included knuckling of the fetlocks, head tucked

between the fore-legs, recumbency,

convul-sions, and death

Nematodiriasis

Infestation of the intestine or abomasum of

ruminants by Nematodirus species It is

endem-ic in some parts of the UK Disease develops suddenly and leads to dullness and loss of con-dition, with black diarrhoea and dehydration;

in lambs, death may follow in a few days

PreventionAs the eggs can survive over win-ter, the life-cycle can be broken by not using the same lambing ground in successive seasons Routine dosing of lambs in susceptible areas can be effective

Nematodirus

Parasitic worms of, particularly, lambs; also

sheep and calves N battus infection is

trans-ferred from one season’s lambs to the next

as large numbers of eggs are deposited on pasture Development of the eggs occurs only after exposure to cold and moisture (See WORMS.)

Nembutal

(see PENTOBARBITONE SODIUM)

Neoarsphenamine

A drug effective against BLACKHEAD OF TURKEYS It has been largely superseded by dimetridazole and nifursol

Neomycin

An aminoglycoside antibiotic obtained from

Streptomyces fradiae It must not be given by

injection, owing to resulting kidney damage Its action closely resembles that of strepto-mycin It is used, sometimes in combination with other medicaments, in a number of veteri-nary formulations A topical spray of this antibiotic has caused profound deafness in children (See DEAFNESS.)

Neonatal

Neonatal diseases are those of the newborn

Neoplasm

Neoplasm means literally ‘a new growth’, and is applied to tumours in general

Neospora Caninum

This parasite was discovered in Norway in

1984, and later recognised in Sweden, the USA, Australia, and the UK in 1990

Cause A protozoan, named as above, and

resembling Toxoplasma gondii Congenital

infection occurs in cattle, dogs, and cats

482 Necrotic Enteritis

N

SignsInfected animals may develop ataxia, a

fleeting paralysis, and nystagmus Meningitis

appears in some cases The parasite may also be

found in aborted ovine fetuses

Neoteny

The retention of juvenile activities and

appear-ance into adulthood It is the basis of

populari-ty of some breeds of dog that remain as playful

as puppies throughout their life The extreme

example is an amphibian, the axolotl or

Mexican walking fish, which rarely matures to

the adult stage

Nephrectomy

Nephrectomy is the name given to the

opera-tion by which one of the kidneys is removed

(See KIDNEY,DISEASES OF.)

Nephritis

Inflammation of the kidneys (see KIDNEY,

DISEASES OF;LEPTOSPIROSIS)

Nephrolithiasis

The presence of a stone (calculus) in the pelvis

of the kidney

Nephron

The structural unit of the kidney (see KIDNEYS)

Nephroptosis

‘Floating kidney’ – abnormal positioning of the

kidney (see KIDNEY,DISEASES OF)

Nephrosis

This is a disease of the kidneys, involving

dam-age to the tubules It leads to albuminuria and

often to oedema (See also KIDNEY,DISEASES OF.)

Nephrosis, Infectious Avian

A disease of chickens (See GUMBORO DISEASE;

INFECTIOUS BURSAL DISEASE.)

Nephrotic Syndrome

(see NEPHROSIS)

Nephrotomy

Surgical incision into a kidney

Nerve Block

Anaesthesia of a nerve or nerves supplying part

of the body to assist diagnosis or treatment

Often used in diagnosing the cause of lameness

in the horse

Nerves

The nerves are fibre-like tissues that convey

impulses (‘messages’) between the central

nervous system and other parts of the body The basic unit of the nervous system is the neuron,

a cell with at least 1 projection Bipolar neurons have 1 long projection, the axon, and 1 short branching projection, the dendrite A typical neuron (multipolar) has several dendrites but usually only 1 axon (nerve fibre)

Dendrites conduct nerve impulses towards the nerve cell; axons conduct away from it

A synapse is a point or area where 1 neuron

is able to make contact with another; the contact being between the axon of 1 neuron and a dendrite of another neuron, or between the axon of 1 neuron and the cell of another neuron Any neuron may connect with axons or dendrites of several other neurons

Nerve fibres may be myelinated (enclosed in

a sheath) or unmyelinated (see MYELIN) Some nerve fibres (axons) convey impulses to brain or spinal cord from skin or sense organ, and are termed sensory or afferent Their impulses are passed, through connecting links or interneu-rons, to motor or efferent nerves from brain or

spinal cord (but see spinal reflex under SPINAL CORD –Functions)

Nerve impulses are dependent upon the permeability of cell membranes There is a potential difference of about 70 to 80 millivolts between the inside and the outside of an axon – the inside being the negative This is owing to the fact that in a resting state the cell membrane

is permeable to K(+) and Cl(–) ions, but not to Na(+) ions Stimulation of the nerve results in the membrane becoming permeable to the sodium ions, which flow in causing the inside

of the axon to carry a positive electrical charge instead of a negative one A so-called depolari-sation wave is set up, ‘self-perpetuating’, along

1 neuron after another A single nerve fibre can send about 1000 separate impulses per second

ACETYLCHOLINEis released by somatic (mus-cle) nerve fibres at synapses between neurons

on either side of ganglia, and also at the junc-tion of motor nerve endings and voluntary (striated) muscle Acetylcholine is released also

at synapses by parasympathetic nerve fibres

NORADRENALINis released at synapses of sym-pathetic nerve fibres, and at their junction with smooth (unstriated) involuntary muscle fibres

Nerves, Injuries to

Continued or repeated severe pressure upon a nerve trunk may be sufficient to damage it and result in paralysis; severe bruising in which a nerve is driven against a bone with considerable force may produce paralysis or inflammation of the nerve; a nerve may be severed along with

Nerves, Injuries to 483

N

other tissues in a deep wound; fracture of a

bone, such as the 1st rib, may produce rupture

of any nerves that lie upon or near to it; and

other accidents may also involve the nerves of

the part A nerve may sometimes be injured at

its origin before it leaves the brain or spinal cord

by haemorrhage (See also under IMMUNISATION.)

SignsSometimes, it is not until after a wound

has healed that the injury to the nerve becomes

obvious In ‘radial paralysis’, or in other cases

where large and important motor nerves have

been damaged, the resulting paralysis of the

muscles they supply is seen at once (See RADIAL

PARALYSIS.) Atrophy of muscles results

(See FACIAL PARALYSISfor another example of

a nerve injury.)

A tumour, such as a neurofibrosarcoma or (in

the cat) a lymphosarcoma, may press upon or

infiltrate the brachial plexus causing progressive

lameness and pain (See BRACHIAL.) Another

tumour is a NEUROMA

If a nerve is cut, the distal part degenerates

This is called Wallerian degeneration

Neuritis(see under this heading)

Nervous System

(see CENTRAL NERVOUS SYSTEM)

Nervous System, Diseases of

(see BRAIN,DISEASES OF;ENCEPHALITIS;

BOTU-LISM; CHOREA; DISTEMPER; CANINE VIRAL

HEPATITIS; TETANUS; RABIES; SPINAL CORD;

LISTERIOSIS; etc.)

Nettle-Rash

(see URTICARIA)

Neurectomy

Neurectomy is an operation in which part of a

nerve is excised The operation is sometimes

performed to give relief from incurable

lame-ness in the horse, but only a few months’ work

may be gained

Neurilemma

Neurilemma is the thin membranous covering

of nerve fibres

Neuritis

Inflammation affecting nerves or their sheaths

It is often accompanied by pain (neuralgia),

sometimes by spastic paralysis Causes include

viral infections, allergies, malnutrition, and

poisoning, as well as physical injuries (See

NEUROMA; NERVES, INJURIES TO; and under

IMMUNISATION.)

Neuroglia

A fine web of tissue and branching cells which supports the nerve fibres and cells of the ner-vous system

Neuroleptanalgesia

A state of combined sedation and analgesia It is used for carrying out minor surgical procedures where full anaesthesia is not required A combi-nation of a sedative, e.g acepromazine, and a powerful analgesic, e.g pethidine, is used

Neuroma

A tumour connected with a nerve, and very painful

Neuron

Neuron is a single unit of the nervous system, consisting of 1 nerve cell, with all its processes

(See illustrationand also NERVES.)

Neurotropic Virus

Neurotropic virus is one which shows a predilection for becoming localised in, and fix-ing itself to, nerve tissues The best known of these is that of rabies Rabies virus enters the body through torn nerve fibres at the seat of an

484 Nervous System

N

A typical neuron: A – dentrites, B – nerve cell body,

C – nucleus, and D – axon (After Francis,

Introduction to Human Anatomy, courtesy of C V.

Mosby Co.)

injury, such as a bite, and, growing along them,

eventually reaches the spinal cord and brain

Other neurotropic viruses are those of

louping-ill in sheep, and Borna disease in horses and

cattle

Neutering

(see CASTRATION and SPAYING; also VASECTOMY)

Neutrons

Elementary particles with approximately the

same mass as a proton The latter has been

defined as a stable, positively charged

elemen-tary particle found in atomic nuclei in numbers

equal to its atomic number

Neutropenia

A reduced number of neutrophil granular

leukocytes in the blood

(In human medicine, most cases are

attrib-uted to the direct toxic effect of certain

antibi-otics, e.g penicillin and the cephalosporins, or

to immune-mediated mechanisms With this

type of blood dyscrasia patients are at serious

risk of an overwhelming infection.)

Neutrophil

A type of white blood cell which can migrate

into the tissues and engulf bacteria, etc (See

under BLOOD;ABSCESS.)

New Forest Disease (Infectious

Bovine Keratitis)

A painful eye condition which can lead to

blindness if neglected (See EYE,DISEASES OF.)

New Forest Fly

A blood-sucking fly, found in many parts of

Britain Hippobosca equina attacks horses and

cattle It deposits larvae (not eggs) in the soil

When disturbed, it makes a characteristic

side-ways movement (See FLIES.)

Newcastle Disease

An infectious, febrile notifiable disease of

chick-ens, turkeys, ducks, pigeons and wild birds

Globally, it is the most economically important

disease of livestock Aviary birds, particularly

finches (canaries, etc.), may be infected by wind

spread Waterfowl can be infected but clinical

dis-ease is rare In humans, conjunctivitis is the main

clinical sign, but people working with infected

birds may develop an influenza-like illness

CauseParamyxovirus

SignsThe first sign noticed in laying birds may

be a drop in egg yield with the production of

pale, misshapen and/or soft-shelled eggs According to the virus strain, infected birds develop respiratory or nervous signs; it is rare to find both together Severe breathing difficulties develop in birds affected with the respiratory strain In the nervous form, torticollis, paralysis

of the wings or legs and impaction of the intes-tine are features In mild cases, the main clini-cal sign may be diarrhoea, usually black Mortality varies Egg production may recover, but not to its former level

Control Live and inactivated vaccines are used Vaccination regimes can vary according

to local circumstances and must be established

on the basis of veterinary advice; the manufac-turer may need to be consulted Live vaccines include the Hitchner B1; they are administered

in the drinking water, by beak-dipping, by eye-dropper or by aerosol spray The manufacturer’s directions must be strictly followed in each case The inactivated vaccine is used for sec-ondary vaccination after primary immunisation with live vaccine It is administered intramus-cularly into the thigh muscle or subcutaneously into the back of the neck

It should always be assumed that, in the vicinity of an outbreak, every flock to be vacci-nated is incubating the disease The incubation period is around 21 days and it takes 10 to

14 days to build up an immunity

Newfoundland

A large breed of dog developed in Canada to rescue people from rivers and the sea; it is a powerful swimmer It is long-haired and usually black or brown Hip dysplasia, aortic stenosis, ununited anconeal process and osteochondritis may be inherited

‘Newmarket Cough’

(see EQUINE INFLUENZA;COUGH)

Niacin (Nicotinic Acid)

One of the vitamin B group, present in most animal feeds, and produced in the digestive system from tryptophan With maize feeding,

a niacin deficiency may occur It has been suggested that niacin supplements benefit dairy cows, as synthesis of the vitamin in the rumen may not be sufficient, which was formerly thought to be the case In dogs a niacin defi-ciency causes ’BLACK TONGUE‘ (See SHEEPDOGS;

VITAMINS.)

Nicking

This is defined in the Docking and Nicking of Horses Act 1949 as ‘the deliberate severing of

Nicking 485

N

any tendon or muscle in the tail of a horse’ The

practice is illegal

Nicotine Poisoning

Nicotine poisoning has killed cattle dressed

with nicotine against warbles, and may also

arise from the old practice by shepherds of

dos-ing their flocks with tobacco against parasitic

worms Poisoning has also been reported in

poultry when perches have been painted with

nicotine sulphate to try to control red mite

(Dermanyssus galinae).

Nicotinic Acid

One of the vitamin B group present naturally in

the body and convertible to NIACIN

Nictitating Membrane

The ‘3rd eyelid’, or haw, consists of a plate of

cartilage covered with conjunctiva, and having

lymphatic tissue and the Harderian gland

Often pigmented, the membrane is always

prominent in breeds of dogs such as the

blood-hound and St Bernard In other breeds of dog,

and in the cat, its protrusion across part of the

eye may indicate general debility if bilateral;

other causes include the presence of a foreign

body, ulceration, a nerve injury, or occasionally

a tumour

‘Night Blindness’

‘Night blindness’ is seen in vitamin A

deficien-cy and early progressive retinal atrophy (see EYE,

DISEASES OF)

NIGHT LIGHTING

Night lighting is commonly practised in

poultry houses, using 40-watt lamps to give a

14-hour day, or 1500-watt lamps for three

20-second exposures a night The object is

increased egg production during the winter

months, and the effect is due not merely to the

provision of extra feeding-time, but also to the

influence of light indirectly on the ovaries

However, an investigation carried out in

con-junction with the ADAS into eye abnormalities

in turkey breeding flocks, leading to blindness,

showed that the cause was continuous artificial

light Seventy per cent of poults showed

symp-toms after 5 weeks of this, and it was proved

that it was the continuity and not the intensity

of the light which was doing the damage

NIGHTSHADE POISONING

The nightshades comprise garden or black

nightshade (Solanum nigrum), woody

night-shade or bittersweet (S dulcamara), and deadly

nightshade or belladonna (Atropa belladonna).

(See GARDEN NIGHTSHADE POISONING; BITTER-SWEET; and ATROPINE POISONING)

Nigroid Bodies

Nigroid bodies are black or brown irregular outgrowths from the edges of the iris of the horse’s eye (See IRIS.)

Nipah Virus

Nipah virus is responsible for a disease of pigs

in tropical areas It causes fever, nervous signs, respiratory difficulties and abortions An out-break of encephalitis among pig farmers in Malaysia, caused by the virus, resulted in the slaughter of 1.1 million pigs (out of a total pig population of 2.4 million) on 956 farms in an effort to control the outreak Only 796 pig farms remained Of 256 people who suffered from encephalitis, 105 died The infection is thought to have originated in flying foxes

Nipple-Drinkers

Nipple-drinkers are popular in pig and poultry enterprises as they supply water on demand without using troughs, and avoiding the possi-blity of drinking water being fouled Similar drinkers are available for use by dogs in kennels Animals may have to be taught how to use them

Nipples

Infection and necrosis of sows’ nipples are not

uncommonly caused by Fusiformis netrophorus,

and may lead to the death of piglets from star-vation (See also MAMILLA– Mamillitis.)

Nit

Egg of louse or other parasitic insect

Nitrite Poisoning

Poisoning as a result of eating plants with a high potassium nitrate content is common in some

of the western parts of the USA The nitrate is reduced to nitrite by substances within the plant under certain climatic conditions, and when such a plant is eaten the nitrite is rapidly absorbed from the digestive system and con-verts haemoglobin into methaemoglobin This

is incapable of giving up its oxygen to the tissues and as a result the animal dies

Sodium nitrite is used for curing meat and has found its way into swill, causing fatal poi-soning in pigs The main symptoms observed were vomiting, squealing, and distressed breathing Nitrite poisoning has also occurred,

in piggeries with poor ventilation, from con-densation dripping down It may arise, too, in grazing animals where nitrogenous fertilisers

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have been spread during dry weather, or before

rain has had time to wash it all in This could

be called nitrate poisoning, but the nitrate itself

has a fairly low toxicity, being converted into

the poisonous nitrite The nitrate content

of heavily fertilised plants may increase the

animal’s intake of nitrates

Treatmentconsists of methylene blue

intra-venously, and ascorbic acid (See NITROSAMINES.)

Signs include abdominal pain, sometimes

diarrhoea, weakness and ataxia, dyspnoea, rapid

heart action and, especially, cyanosis The

mucous membranes appear brown, due to the

presence of methaemoglobin Convulsions,

coma, and death may follow

In a case reported by the State Veterinary

Service, acute poisoning was seen in 13 cows

after they had been brought into a shed An

hour or two later, 2 were dead, 2 were dying

and 9 were very distressed, showing dyspnoea,

salivation, cramping pains and head-pressing

Their blood was dark brown The local hospital

was asked to make up a 4 per cent solution

of methylene blue, which they did within

15 minutes When each cow was injected

intravenously with 500 ml, the response was

dramatic and reminiscent of that seen in

the successful treatment of milk fever with

calcium Sequelae of this event were abortion in

2 of the cows and a change in temperament,

normally quiet cows becoming wild The

source of the nitrate was believed to be straw

bedding contaminated with fertiliser from

broken bags

Fatal nitrite poisoning of pigs has occurred

following the use, for drinking purposes, of

rainwater containing decaying organic matter

Nitrites

Nitrites are salts which, in excess, convert

haemoglobin into methaemoglobin, and may

cause death from lack of oxygen (See NITRITE

POISONING; NITROSAMINES.)

Nitrofurans

A group of drugs developed in the USA during

the 1940s, and including nitrofurazone,

fura-zolidone, and nitrofurantoin (for urinary tract

infections) They are effective against a wide

range of bacteria, including Gram-negative;

some against protozoa and fungi It is thought

that they interfere with the carbohydrate

metabolism of micro-organisms The use of

furazolidone and nitrofurantoin for medicines

in food-producing animals is prohibited in the

EU

Nitrogen

(see AIR) For liquid nitrogen see CRYOSURGERY;

ARTIFICIAL INSEMINATION;LIFE AFTER FREEZING

Nitrogen dioxideA reddish-brown heavy gas with an offensive odour This is formed by oxidation, on exposure to air, from the colour-less nitric oxide The latter appears to be the chief oxide of nitrogen produced in the early stages of silage-making

Emissions of this gas from silage clamps have caused human illness and the death of farm animals

SignsDyspnoea, cyanosis, muscular weakness and, in piglets, vomiting

Nitrophenide Poisoning

Nitrophenide poisoning, characterised by paralysis, has occurred in pigs fed medicated meal intended for poultry and containing nitrophenide as a treatment for coccidiosis

Nitrosamines

They are very powerful chemical carcinogens They cause cancer of specific organs irre-spective of the route of administration Some nitrosamines can be formed from nitrite and secondary amine or amide in the acid stomach contents of animals Nitrites used as food preservatives, and high levels of nitrates in drinking water, can be carcinogens

Nitroscanate

A general anthelmintic for use in dogs It acts against both tapeworms and roundworms

Nitrothiazole

The drug 2-amino-5-nitrothiazole is effective in controlling blackhead in turkeys (by preventive medication)

Nitrous Oxide

This anaesthetic is not much used in veterinary practice but, where it is, there is a need for good ventilation, as it interferes with vitamin B metabolism and, in a pregnant anaesthetist, may bring about a miscarriage

Nitroxynil

Nitroxynil, a fasciolicide, is used by injection for the treatment of fluke in cattle and sheep and, given by mouth, against gapeworm in birds Animals must not be slaughtered for meat until 30 days after administration

NOAH

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Infection with Nocardia asteroides in cattle,

dogs, cats, and man It is a saprophytic

inhabi-tant of the soil and belongs to the genus

Actinomycetes It was formerly classified as a

fungus but is now regarded as a bacterium It

has occasionally been isolated from the udders

of cows affected with mastitis, and has been

reported as the cause of ‘incurable mastitis’ in

an outbreak on a Texas farm Involvement of

the liver and mesentery, with marked loss of

condition, thirst, and some diarrhoea – calling

for euthanasia – has been recorded in the dog in

Britain Pleuropneumonia, occasionally also a

skin infection, may result from Nocardia in

dogs and cats

Node

(see LYMPH NODES)

Nodular Panniculitis

An inflammatory reaction involving

subcuta-neous fat, and characterised by nodules which

burst Abscesses and sloughing may occur

(See AUTO-IMMUNE DISEASE, of which the above

is an example, occurring in dogs.)

Noise

(see STRESS)

Noradrenalin

A hormone secreted by the adrenal gland

medulla It causes increased heart rate, and

con-stricts the blood vessels, causing a rise in blood

pressure (See NERVES.)

Normal Saline (Physiological

Saline)

Normal saline (Physiological saline) is a

solution of sodium chloride in sterile distilled

water, which is isotonic with the strength of

this salt in the bloodstream – that is, about

0.9 per cent for mammals (See also

DEHYDRA-TION;DEXTRAN.)

Normoblast

Normoblast is a red blood cell which still

con-tains the remnant of a nucleus

Northern Fowl Mite

This can infect canaries as well as poultry, and

has caused allergic reactions in poultry-keepers

in Israel (See MITES.)

Norwegian Scabies

This is a form of sarcoptic mange The skin

becomes red, the hair falls out in patches, and

there is intense pruritus

Nose and Nasal Passages

The ‘nose’ of an animal, which is more often termed the ‘muzzle’, or ‘snout’, according to the species, serves 3 important functions It forms the outermost end of the respiratory passage; it

is the organ of smell; and it contains some of the end-organs of the sense of touch

HorsesExternally, the rims of the nostrils are built up on a basis of cartilages covered over by

a fold of delicate skin possessing long tactile hairs The cartilages are not complete laterally, thereby allowing the nostrils to become greatly distended during occasions of emergency Situated at the upper and outer part of each nostril there is a pouch-like sac which opens into the nostril at one end, but is blind at the other This is often called the ‘false nostril’ Lying just within the entrance to the nasal passages about an inch or so inside each nostril

is the lowermost opening of the lacrimal duct carrying tears secreted by the lacrimal gland of the eye

Internally, each nostril, and the nasal passage

to which it gives access, is completely divided from the other by the septum of the nose and its associated structures This is composed

part-ly by the vomer bone, and partpart-ly by a wall of cartilage which is continuous with the cartilages

of the nostrils The walls of each passage are lined by mucous membrane which is reflected

on to the two turbinated scroll-like bones that are found in the passage; this membrane, being well supplied with blood, and being

continual-ly moist from the secretion of its mucin glands, serves to warm and moisten the incoming air before it passes to the lungs, and to extract the larger particles of dust, soot, etc., that the air picks up, by causing them to adhere to its sticky surface The entrance to the air sinuses of the skull leads out from the posterior part of each passage, the mucous membrane lining the sinuses being continuous with that

of the nose (See SINUSES OF THE SKULL.) The end-organs of the sense of smell are scat-tered throughout the nasal mucous membrane

in the upper parts particularly The olfactory nerves from the brain, which pass out of the cranial cavity into that of the nose by way of the ethmoid bone, are distributed to these end-organs Posteriorly, the nasal passages lead into the pharynx

CattleThe nostrils, situated on either side of the broad expanse of moist hairless muzzle, are smaller and thicker than in the horse No false nostril is present, and the opening of the lacrimal duct is not visible

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