The control of the sheep‐tick (Ixodes ricinus L.) by treatment of farm stock

Abstract

The sheep tick is practically confined to the rough hill‐grazings in Britain where the chief domestic hosts are sheep and cattle. The practical difficulties of treating sheep, lambs and cattle are outlined. Sheep with lamb‐at‐foot, and suckling Galloway and Kyloe cows unused to handling, are the biggest problems.Research on anti‐tick materials having been done chiefly by commercial firms, public knowledge is very scanty. Thirty‐nine experimental and commercial anti‐tick preparations were tested on sheep, lambs and cattle.A sheep dip must be safe, easily mixed, have lasting effect, be capable of dealing with all or most of the ecto‐parasites present and reasonably cheap. So far no experimental dip has surpassed a commercial product comprised of sodium arsenite, ground derris root, cresols and woolfat. In the case of the female, tick, with 30 sec. immersion this dip kills all ticks attached at time of dipping and keeps sheep free of ticks for 7‐10 days, while reinfestation is not complete until 3—4 weeks after dipping. Derris is chiefly responsible for duration of residual effect in this dip. Unlike arsenic, derris kills a proportion of ticks before they can attach and thus lessens tick‐worry and the chances of disease transmission. The dip has no ill‐effects on sheep.The present method of assessment by tick counting does not quite show the full lethal effect of dips. No improvement in the method seems possible.Changes in the bath fluid and in residual protection for sheep were studied at different stages of normal dippings (c. 200‐300 sheep) in spring. Herdwick ewes and Black‐faced yearlings each finally carry away about 1/2 gal. (2.28 l.) of dip fluid in their fleeces. A large quantity of foreign solid matter is added to the bath by sheep as dipping progresses; arsenic content remains unchanged while derris is somewhat reduced. The ground derris root particles are thought to be trapped in the meshes of the fleece as excess dip fluid runs back to the bath. Surface tension increases from about 48 to 50 dynes/cm. Residual protection for sheep against ticks lessens as dipping progresses, probably due to progressive reduction of derris in the bath. On the average, provided each sheep gets its share, the dip could furnish each sheep with not more than 0.08 oz. (2.27 g.) ground derris root, 0.18 oz. (5.10 g.) arsenic (as As2O2), and woolgrease at the rate of 10‐17% (0.64‐1.12 oz. or 18.14‐31.75 g.) of the weight naturally present in the fleece (6.40 oz. or 181.44 g.). The dip is effective against all ecto‐parasites except blowfly larvae.Light smearing with vaseline or woolgrease kills attached female ticks within 24 hr. 16% of female ticks on Cheviot yearlings in spring are attached in long‐woolled areas. For this and other practical reasons, sprays and smears are useless for sheep. A derris‐Fuller's earth dust is as effective against ticks as the dip described above but is difficult to disperse in woolled areas. The chief drawback with derris dust, however, is that at certain times it can blind half the sheep. For sheep, the dip is superior to any known dust.Young lambs cannot be dipped: they must be treated on the pasture by methods described. Derris‐Fuller's earth dust is superior to a derris smear, giving protection of a similar order to the dip on sheep. Among thousands of lambs dusted, very much less than 1 % had their eyes affected.Cattle can be treated in stalls by washing or dusting, if used to handling; if not (with the exception of suckling Galloway and Kyloe cows), they can be jetted in stocks. Of several derris dusts, washes and jetting fluids, the best is one containing derris, soap and water. This gives protection of the same order as that with dip on sheep.The derris materials described are the best yet produced for anti‐tick treatment of stock. Cube (Lonchocarpus) root of similar rotenone content to derris root gives similar results to derris in the dip for sheep, dust for lambs and wash for cattle.Attempts have been made to reduce tick populations on grazings by serial anti‐tick treatment of stock. The maximum serial interval possible with derris‐containing materials is 2‐3 weeks. Because lambing prevents dipping for about 6 weeks, this permits about 50 % of the female ticks to escape and breed on the normal sheep farm in spring. The serial interval, i.e. residual protective duration of anti‐tick materials, requires to be lengthened to 5‐6 weeks to prevent this escape. The research work necessary to show whether or how the duration of residual protection could be increased is suggested.