SKIN PARASITES IN SHEEP.

Otago Witness, Issue 1583, 25 March 1882, Page 7

SKIN PARASITES IN SHEEP.

(New Zealand Country Journal.)

The loss, of wool caused by the skin parasites which infest our flooks is much greater than is generally supposed. Besides the wool actually shed, and loss by rubbing, there is the far mor6 serious loss .occasioned by the constant irritation and inflammation of the skin, set up by these parasites, which causes the sheep to lose condition ; the growth of wool 'is checked, and a loss in quantity, as well as deterioration in quality,' is the result. ' This is not the only loss sustained by the owners' of sheep infected with 1 these ■insects. The sheep being always inarestlesß state, wander about their pastures, destroying nearly as much grass as 'they eat, and they rub against the' fences, breaking wires and causing gaps ; the result being the continual straying and mixing .with other flocks, which is one of the greatest annoyances the sheep-breeder has to contend with. ' In the spring, too,long-w6olled sheep being heavy in 'fleece require the constant attention of the shepherd on account of their liability to get cast on their < backs, and ' a considerable number of sheep are lost every season from this cause, which is mainly due to lice and ticks. These very serious losses may in a great_ mea : sure be avoided, and I write this paper in 'the hope that by drawing the attention of stockowners to the subject, they may be induced to take the necessary measures for coping with this growing evil. The three skin parasites which attack sheep in New Zealand are, the scab {Acarus ovis) or (Peiinatodectes ovis), the louse (Trichodectes sphcerocephalus), and tho tick (Mdophagus ovintis). Until quite recently the scab has undoubtedly been the most formidable of these, but there is a good reason to hope that the day is not far distant when our flocks will be entirely free from this pest. Of ,the 14,000,000 sheep in New Zealand, there were about 700,000 infected with scab on the 31st December last, being some 200,000 less than at the same date in the previous year, and this number is rapidly being reduced. The sheep louse bids fair to give almost as much trouble as the scab acari. Although a comparatively recent importation, its increase has been so rapid that a crossbred or lorigwoolled flock free from lice is now the exception. The sheep tick, although troublesome enough^ is not to be compared with the acari or the lice, for the damage it causes. These three parasites produce in a different degree much the same effect on the sheep — i.e., intense irritation of the skin, accompanied with loss of wool and condition. The scab acari burrow into the skin, where they breed, and they cause an eruption of the skin which hardens into a thick scab ; the lice and ticks cause a very slight eruption, and breed in the wool.

In this paper I propose to speak more particularly of tho sheep louse, as it is probably the least known, and it is the parasite which we have most to fear in tho future, as it is undoubtedly gaining ground. The popular impression with regard to lice in animals is, that j they are the result of poverty of the blood, but scientific men of tho prosent day toll us thero is so such thing as spontaneous generation, that animals infested with parasites must previously have come into contact with the germs of the insect. However this may bo in the case of lico in horses and cattle, 1 think that the following fact, which I boliovo is undisputed, goes a groat way towards proving tho germ theory in tho case of lice in sheop : tho sheep louso did not appear in this country until somo eight or nine years apro, when it is supposed to have been introduced in some imported long-woolled rams. Although prior to that date sheep were in many instances kept in just as poverty-stricken a state as we occasionally see them now, sheep in low condition did not then, nor do thoy now, necessarily breed lice. It is also generally believed, that lice confine themselves to low - conditioned animals. From my own observation, I am inclined to believe that they are to bo found on most animals, irrespective of condition, but that they do not thrive and increase, and consequently are not noticed, on perfectly healthy and well-doing animals. One instance I knew of, a flock of Leicester ewes which were poor and very bad with lice j they were put on to

good feed, and in a few months, had* apparently thrown off the lice, and were looking well. A little later, being allowed to go back in condition, they became worse than ever, the lice literally swarming over them. 1 had frequent opportunities of examining these sheop, and when they were looking at their best, I could always find lice. Sheep lice begin to die off about the end of October, when the weather commences to get warm. T think this may lie attributed to the yolk rising more freely at this time of the year, and choking the air passages of the insect. Both lice and ticks disappear when sheopare shorn, apparently because there is not sufficient shelter left for them ; they loavo the ova attached to the wool, and about February, when thore is sufficient length of wool to shelter them, the young insects 'appear. Lice are not readily detected until about April, when loose wool may be seen to rise on the back ; this is caused by the insect cutting the fibres of wool , noar the skin with tho sharp nippers with 1 which it is furnished ; this loose wool is soon rubbed off, and a bare patch appears', which . gradually enlarges as the insects increase, until, as I have seen in some cases, a fourth or moroi of the wool is lost. ' . . , All classes of long-woolled and crossbred sheep are subject to lice, but it is rarely found ( on the merino,— the density of the wool and abundance of yolk in the merino may posubly account for this. Tho old saying, 'if a thing in worth doing, it is worth doing well,' winch is so applicable to farming, applies equally well to the management of stock ; it is just as necessary for the farmer to keep his sheep in good order, as it is for him to keep his land in good heart. As with the land so with the sheep, 1 the better attention they get the better the, result. There is no doubt, that as _ long as' sheep are kept in really good condition, they will keep comparatively free from lice andticks, but stock-owners cannot always do this,, the seasons here aro so variable that no one can calculate with any certainty, as to what amount of stock his farm will carry through tho winter ; they must thoreforo have recourse to dipping, which properly administered, is a certain cure for all parasites. Some diversity of opinion exists as to the best time to do this ; dipping off the shears is advocated by somo, as at this time loss material is required, but it is extremely doubtful whether any ordinary dip will destroy the ova, unless the dip is kept hot, which adds considerably; to the expense. The more general practice is to dip about March or April, when there being more wool, tho dipping material will remain a longir time, acting as a preventive, and will pro ,bably be sufficiently strong to kill the young insects as they hatch out. Another reason ifl favour of dipping at this time is, that the fannor having bought his stock for tho winter, will not be so likely to re-infect his flock by sheep purchased through the pubic saleyards, which aro almost sure to be infested with lice. Dipping to be of real good should bo universal. It is very discouraging for a sheepowner who has gone to the trouble and expense of dipping his flock to find his neighbours' infected sheep mixed with his own. The CO &P of dipping is about l^d per head, and when it is considered that for this small cost, the sheep are freed from these pesjts, and consequently;, having nothing to worry, them, are enabled to face the. , winter in good heart, and in addition thrive, 'and no not trouble the fences, and the , loss of ,wppl"is avoided, there ( can be no question, as to , the',, wisdom of dipping,; and no stock-owner' shoii]d hesitate 1 to do go. There are' various compounds sold" for dipping, most, of which,a,re,said to be efficacious if *used with cold wate,^; X should strongly ad vide those,who'can procur'e'fuel at.a reasonable cp'sp, to'dipat a heat. of 80,deg. 6r'9O deg. dip is. much more ' penetrating, and is, riiore likely to,' destroy tho^ ova of tn'e parasitdsl |I should also recommend ' those interested,' to watch the effect' of the, various 'dips' on their ( pwn and ■ their neighbours' flocks ; and to 'choose' that dip which, while destroying the parasites effectually, leaves the least stain in the wool. ' It would greatly , facilitate the dipping of sheep, in agricultural districts, if dips wero erected by priyate, enterprise, at the various centres, where farmers 'bpuld get their smalL flocks dipped .for 1 a ( moderate charge. Very small flocks do 'not warrant the necessary outlay, and in other instances, want' of water is the difficulty. There is' but little , doubt, that if tliese difficulties were overcome by some such means as I have suggested, dipping sheep would become, much more general, to the decided advantage of the owner, and the country at large.

Reginald Foster.

Amberley.