THE STATION.

Oamaru Mail, Volume IV, Issue 1003, 8 July 1879, Page 3 (Supplement)

THE STATION.

DISEASES IN SHEEP. The following is the memorandum on the pai-asitic insects which infest sheep, producing skin diseases, and depreciating the value of both sheep and wool, by Dr. Hector, Director of the Colonial Museum:— THE SCAB. This disease of the sheep, which is anal ago us to the mange in the lower animals, and to the itch in man, is the greatest scourge to which sheep are liable. A disease similar, if not identical in its nature, has been known from the earliest pastoral history of Europe. The opinion is held by some authors that it may originate from various causes, such as bad keep or starvation, producing a low condition of the flock ; but there is abundant proof that in the Southern Hemisphere this disease is entirely due to contagion, and, as prevention is better than cure, wherever flocks are discovered to be infected every precaution should be taken to isolate the diseased sheep and prevent contact with the clean. To this end, legal enactments, if vigorously carried out by the inspectors, are sufficient to check the evil, which cannot, however, be thoroughly exterminated until the whole country is fenced. The cause of scab in sheep is the presence of minute insects belonging to the natural-. Acaridce, or true mites. Dermatodectes ovis, is about of an inch in length, the male i; lrcmg slightly smaller than the female, These insects have soft thin-skinned bodies, and possess style-like mandibles, forming a retractile horny tube, which enables them to burrow beneath the skin and bury themselves' within the integuments of the animal they infect. A red spot marks the place where the insect enters the skin. On the tenth or twelfth day this spot begins to swell, and a pustule rapidly forms, which about the sixteenth day breaks, and the female appears with progeny of from eight to fifteen young acari attached to her legs. These immediately burrow beneath the skin, where thegdn their turn grow and propagate. JPftese numerous pustules, as they hard crusted scab, henco of the disease. The excessive inflation produced by the presence of :ihese acari induces the animal to rub against every hard object, and also to bite itself wherever it can reach, thus tearing the wool and producing a very ragged 'fleece, by which the presence of scab in flock is easily recognised. The usual progress of the disease is as follows:

The appearance of the scab in its earlier stages is indicated by a rough and inflamed condition and reddish hue of the skin. When closely examined the skin also feels granular to the touch. These granulations are the germs of the pustules which contain the acari at a later stage of their growth. A few days further on, an extensive eruption of pustules is detected about the upper parts of the back and towards the shoulders, and the slie.ep furiously scratches itself against every

post, stump, tree, or other object in the way. The pustules speedily ripen, break, and run together, forming the characteristic incrustation or scab. The skin under the scab is raw and sore, and continues so until the scab dries and scales off. The acarus or parasitical insect, which had its receptacle in the pustule, nsoon as the latter dries moves away to ;> clean part of the skin, and, burrowing there, sets up a new point of inflammation and a further extension of the disease.

Thus shifting its position, the acarus spreads the scab all over the sheep's body, and, by adhering to the various rubbing places where the diseased sheep have been scratching themselves, the insect is transferred to the fleece of any luckless sheep that touches the spot; and if but one pair, male and female, or a pregnant female alone, effect a lodgment on the fleece of a clean sheep, so quickly do the} 7 propagate that in a few weeks from the first infection the sheep will be covered with these parasites. The sheep in this diseased state quickly loses condition, its skin becomes foetid, scurfy, and sorelooking, its fleece harsh, rugged, and turn off in patches, its gait feeble and staggering, its whole appearance repulsive, and at 110 very distant period it succumbs to the disgusting disease.

The scab insects which are Latched at the later period of tho summer generally survive over the winter, and, whether fed on the juices of the sheep's skin or existing by means of the moisture obtainable on the rubbing places to which they adhere, they often retain sufficient vitality in the ensuing spring to generate the scab again in sheep which were apparently or actually made clean in the autumn or winter previously. Where the latter has been the case—that is, where there has been a positive cure or eradication of the disease, and it nevertheless returns again with the opening warmth of spring—the contagion has probably been reproduced by the rubbing places frequented by the sheep. All such rubbing places should therefore be purified by fire, and this can be best and most conveniently effected by setting fire to the grass and scrub on the run or pasture ground. The young acarus, if kept apart from all moisture, quickly perishes and dries up ; but the survival of the adult insects from the autumn to the following spring is sufficient to show that great perseverance must be exercised in the efforts to eradicate the scab.

The disease will appear again and again, and some so-called cleansing solutions never do affect the germs of the disease by destroying the young acari burrowing deep in the sheep's skin ; whilst other applications, which are sufficiently destructive to the immature insects, cannot be applied effectively without at the same time doing mischief to the health of the sheep, and great injury to the staple of the wool.

Except in a very early stage scab is easily distinguished from all other cutaneous diseases to which sheep are subject, on the one hand by the symptoms described above, which are peculiar to scab ; and, on the. other, by coutrast with the distinctive appearances so well known to persons of ordinary experience among sheep, which denote grass seeds, wounds, fever spots, prickly heat, and rubbers, the only ailments for which scab is at all likely to be mistaken. Cure.—ln the words of Youatt," the cure of scab lies in the destruction of this insect;" This is a simple and most important view of the case, and the only question is—What is the best remedy, and the simplest method of application 1 Various substances have been recommended at different times for the cure of scab, some of them, such as compounds of arsenic or corrosive sublimate, being of a very dangerous nature, requiting great judgment and care in their application. Tobacco has also its advocates ; but in every case when the substance used is of a strong poisonous nature it is more or less absorbed into the system of the animal to which it is applied, and death may result instead of cure. The object to be attained, therefore, in the cure of all diseases of sheep produced by insects is the destruction of the insect by a substance which will be harmless to the sheep if absorbed into the system. Sulphur offers all the requisites of an innocuous application for sheep, and at the same time a certain specific for destruction of all insect life ; but for this purpose it must be applied in the form of a soluble salt by its combination with some alkali, such as soda or lime. There is no doubt that the real value of Gissard's fluid, so much used by gardeners, entirely depends on sulphur in a state of thorough solution; and several patent sheep-dipping compositions as cures for scab, rest on the same basis. The manufacture of soluble sulphur as hyposulphite of lime is so simple that any shepherd could do it with little instruction. The following is one of the best processes in use : —Take in the proportion of one part by weight of the best quality of fresh quicklime, and slake it carefully without an excess of water. Crush the slaked lime with a heavy roller, and pass it through a fine sieve, so as to remove all the small lumps. Add to it twoparts by weight of flowers|of sulphur, mixing the two ingredients thoroughly, and again passing them through the sieve, so as to insure perfect incorporation. Shovel the mixture thus obtained into a boiler containing boiling rain-water, in the proportion of 91b. of the mixture to every ten gallons of water, and, stirring well from the bottom, keep on the boil for half an hour, when the liquor is ready for use. Or another method is to put the sulphur into the water and boil for fifteen minutes, stirring all the time ; then add the quicklime unslaked, and keep on stirring until the liquid is of the color of dark brandy. This latter method is preferred for making small quantities. The temperature of the dip should be maintained at 110 deg. to 120 deg., and each sheep should be soaked in the dip for two minutes, during which time their heads should be ducked twice, and the solution well rubbed into the fleece with a crutch. The process of dipping should be repeated within fourteen days. SHEEP LOUSE.

Sheep are sometimes infested with a species of louse, which belongs to the same genus as the louse of the horse, and is named Trichodectes sphce,rocephalus (or Pediculus ovis of the older entomological writers). It i§ characterised by having the head nearly orbicular, rough and fringed with stiff hairs, and the third joint of the antennae longest and clavate. They have distinct jawa, and the abdomen is nine to ten-jointed. They are sometimes found in incredible numbers on the sheep, and produce an eruptive disease resembling scab. They are small active brown-colored insects, and they are found chiefly on sheep in a low condition of health.

Being one of the gnawing lice, it destroys the woql by cutting it near the root. Thi3 animal often makes its appearance in sheep improving iu condition after a long period of poverty of food. . It is seldom seen on a Leicester sheep, because, perhaps, they are seldom in the state to induce it; but hill sheep are not infrequently infested by it, and amazing numbers of tho vermin may be seen on a single sheep, its powers of reproduction being prodigious. It lodges chiefly upon and below the neck, where it is most effectually destroyed by mercurial ointment, which should not, however, be employed in quantity in very cold or very wet weather ; and in these circumstances tobacco-juice and spirit of tar may be safely used. Professor Dick says that in slight visitations of this louse a single dressing of olive oil will cause its disappearance. Such applications are rarely possible in this colony, where the flocks are large and the sheep rarely handled,

but the ordinary dipping as for scab will equally d 'stroy the louse. The Eivrick Shepherd mentions a carious danger to which sheep affected wi'h lice are liable :—" The animal is m danger of being bridled. This is occasioned by the sheep bending its neck exuvmely to claw its throat with its teeth, on which occ ssioiis the teeth often fasten in the wool *_•<> that it cannot disengage them, and it soon loses the power of moving its neck. I have kuown several die in this way." THE WINGLESS SHEEP TICK. The sheep tick, Melophagus ovinus, ia a formidable insect, and must be very annoying to sheep. It is placed by authors in the Hippoboscidce, which are characterised by a horny and flattened body. Its instruments for piercing the skin and almost burying its proboscis and head within it are three in number ; but it adheres firmly to the skin chiefly by means of six legs, which are exceedingly muscular ant) powerful, and armed with strong double-serrated claws. It is a nimble animal, and runs quickly enough about the sheep in search of some favorite spot; but when it has fixed itself it will hang for weeks and months together, and seems as if it lost the power of extricating itself, for it never voluntarily comes away. It varies much in aize, and is sometimes found as large as a horse-bean. It propagates with much rapidity, although not to be compared to the sheep louse in fecundity. During the summer, oval shining bodies, like the pips of small apples and similar in color, may be found attached by the pointed end to the wool. These are not the eggs of the tick, as generally supposed, but the pupa;, which are laid by the female, the egg being developed and hatched in the body of the female. This is a disadvantage in the destruction of the insect, as its life is not easily destroyed when in this stage. sheep bot (CEstrus ovis). Sheep suffer to a great extent in some parts of New Zealand from the presence of this fly, but it does not come under the category of insects which produce skin disease, and will therefore demand a different treatment, which must partake more of the nature of preventive than curative.

This fly deposits its eggs in the nostrils, and by the warmtli and moisture of the part tliey are almost immediately hatched ; the little maggots from thence find their way into the frontal cavities, where they grow until the following summer, when they are then two-thirds of an inch long. 'J'hey are then ejected from the head, enter the earth, and become hard brown pupte, which, in the warmth of the season, are hatched as bot-flies, and they then become an intolerable nuisance to the flocks.

Youatt describes the terror of a flock at the appearance of this pest:—"They gather together with tlieir heads in the centre and their muzzles buried in the soil, if they can find any, and are in continual motion, stamping with their feet and snorting in order to guard their noses against the assault of their puny enemy ; then, perhaps, one of them who is more specially attacked will burst from his companions and gallop across the field, looking fearfully behind him at every step." When several maggots enter the head of one sheep it may cause vertigo or staggers, and end in death. An opinion prevails that the bot-flies are viviparous, the larvsa being hatched within the body of the parent, who deposits in the nostrils of the sheep the perfectly-formed and living grub. This is extremely probable, for during hot weather, both in Australia and in New Zealand, the blow-fly is invariably viviparous, while in the early spring it only lays eggs. The sheep bot is of a dirty-ash or grey color, the face oclireous, eyes brown ; body silvery, spotted with black, having two large white scales at the base ; the abdomen is marbled with yellowish and white flecks, and is hairy at the ends; the legs are ochreons. As has been already stated, the procedure in the case of sheep bot-fly under notice must bs preventive, not curative, and as the aversion of all flies to whale oil is well known, it is recommended to daub with a brush dipped in this oil the heads of the sheep in the first warm weatherjof spring, and it will be found that no flies will then approach them. It may be recommended to shepherds, for the purpose of familiarising them with the true bot-fly, to secure some pupta and place them in a small box where they will hatch out perfect flies. This has been done at the Wellington Museum front specimens sent from Wairarapa. The information given is compiled from various authorities on the subject, and from a valuable resumd of the latest views on the scab disease, which appeared in the New Zealand Country Journal of April and July, 1877.